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1 //===- InstCombineCasts.cpp -----------------------------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the visit functions for cast operations.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "InstCombineInternal.h"
15 #include "llvm/ADT/SetVector.h"
16 #include "llvm/Analysis/ConstantFolding.h"
17 #include "llvm/Analysis/TargetLibraryInfo.h"
18 #include "llvm/IR/DataLayout.h"
19 #include "llvm/IR/DIBuilder.h"
20 #include "llvm/IR/PatternMatch.h"
21 #include "llvm/Support/KnownBits.h"
22 using namespace llvm;
23 using namespace PatternMatch;
24 
25 #define DEBUG_TYPE "instcombine"
26 
27 /// Analyze 'Val', seeing if it is a simple linear expression.
28 /// If so, decompose it, returning some value X, such that Val is
29 /// X*Scale+Offset.
30 ///
decomposeSimpleLinearExpr(Value * Val,unsigned & Scale,uint64_t & Offset)31 static Value *decomposeSimpleLinearExpr(Value *Val, unsigned &Scale,
32                                         uint64_t &Offset) {
33   if (ConstantInt *CI = dyn_cast<ConstantInt>(Val)) {
34     Offset = CI->getZExtValue();
35     Scale  = 0;
36     return ConstantInt::get(Val->getType(), 0);
37   }
38 
39   if (BinaryOperator *I = dyn_cast<BinaryOperator>(Val)) {
40     // Cannot look past anything that might overflow.
41     OverflowingBinaryOperator *OBI = dyn_cast<OverflowingBinaryOperator>(Val);
42     if (OBI && !OBI->hasNoUnsignedWrap() && !OBI->hasNoSignedWrap()) {
43       Scale = 1;
44       Offset = 0;
45       return Val;
46     }
47 
48     if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
49       if (I->getOpcode() == Instruction::Shl) {
50         // This is a value scaled by '1 << the shift amt'.
51         Scale = UINT64_C(1) << RHS->getZExtValue();
52         Offset = 0;
53         return I->getOperand(0);
54       }
55 
56       if (I->getOpcode() == Instruction::Mul) {
57         // This value is scaled by 'RHS'.
58         Scale = RHS->getZExtValue();
59         Offset = 0;
60         return I->getOperand(0);
61       }
62 
63       if (I->getOpcode() == Instruction::Add) {
64         // We have X+C.  Check to see if we really have (X*C2)+C1,
65         // where C1 is divisible by C2.
66         unsigned SubScale;
67         Value *SubVal =
68           decomposeSimpleLinearExpr(I->getOperand(0), SubScale, Offset);
69         Offset += RHS->getZExtValue();
70         Scale = SubScale;
71         return SubVal;
72       }
73     }
74   }
75 
76   // Otherwise, we can't look past this.
77   Scale = 1;
78   Offset = 0;
79   return Val;
80 }
81 
82 /// If we find a cast of an allocation instruction, try to eliminate the cast by
83 /// moving the type information into the alloc.
PromoteCastOfAllocation(BitCastInst & CI,AllocaInst & AI)84 Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI,
85                                                    AllocaInst &AI) {
86   PointerType *PTy = cast<PointerType>(CI.getType());
87 
88   BuilderTy AllocaBuilder(Builder);
89   AllocaBuilder.SetInsertPoint(&AI);
90 
91   // Get the type really allocated and the type casted to.
92   Type *AllocElTy = AI.getAllocatedType();
93   Type *CastElTy = PTy->getElementType();
94   if (!AllocElTy->isSized() || !CastElTy->isSized()) return nullptr;
95 
96   unsigned AllocElTyAlign = DL.getABITypeAlignment(AllocElTy);
97   unsigned CastElTyAlign = DL.getABITypeAlignment(CastElTy);
98   if (CastElTyAlign < AllocElTyAlign) return nullptr;
99 
100   // If the allocation has multiple uses, only promote it if we are strictly
101   // increasing the alignment of the resultant allocation.  If we keep it the
102   // same, we open the door to infinite loops of various kinds.
103   if (!AI.hasOneUse() && CastElTyAlign == AllocElTyAlign) return nullptr;
104 
105   uint64_t AllocElTySize = DL.getTypeAllocSize(AllocElTy);
106   uint64_t CastElTySize = DL.getTypeAllocSize(CastElTy);
107   if (CastElTySize == 0 || AllocElTySize == 0) return nullptr;
108 
109   // If the allocation has multiple uses, only promote it if we're not
110   // shrinking the amount of memory being allocated.
111   uint64_t AllocElTyStoreSize = DL.getTypeStoreSize(AllocElTy);
112   uint64_t CastElTyStoreSize = DL.getTypeStoreSize(CastElTy);
113   if (!AI.hasOneUse() && CastElTyStoreSize < AllocElTyStoreSize) return nullptr;
114 
115   // See if we can satisfy the modulus by pulling a scale out of the array
116   // size argument.
117   unsigned ArraySizeScale;
118   uint64_t ArrayOffset;
119   Value *NumElements = // See if the array size is a decomposable linear expr.
120     decomposeSimpleLinearExpr(AI.getOperand(0), ArraySizeScale, ArrayOffset);
121 
122   // If we can now satisfy the modulus, by using a non-1 scale, we really can
123   // do the xform.
124   if ((AllocElTySize*ArraySizeScale) % CastElTySize != 0 ||
125       (AllocElTySize*ArrayOffset   ) % CastElTySize != 0) return nullptr;
126 
127   unsigned Scale = (AllocElTySize*ArraySizeScale)/CastElTySize;
128   Value *Amt = nullptr;
129   if (Scale == 1) {
130     Amt = NumElements;
131   } else {
132     Amt = ConstantInt::get(AI.getArraySize()->getType(), Scale);
133     // Insert before the alloca, not before the cast.
134     Amt = AllocaBuilder.CreateMul(Amt, NumElements);
135   }
136 
137   if (uint64_t Offset = (AllocElTySize*ArrayOffset)/CastElTySize) {
138     Value *Off = ConstantInt::get(AI.getArraySize()->getType(),
139                                   Offset, true);
140     Amt = AllocaBuilder.CreateAdd(Amt, Off);
141   }
142 
143   AllocaInst *New = AllocaBuilder.CreateAlloca(CastElTy, Amt);
144   New->setAlignment(AI.getAlignment());
145   New->takeName(&AI);
146   New->setUsedWithInAlloca(AI.isUsedWithInAlloca());
147 
148   // If the allocation has multiple real uses, insert a cast and change all
149   // things that used it to use the new cast.  This will also hack on CI, but it
150   // will die soon.
151   if (!AI.hasOneUse()) {
152     // New is the allocation instruction, pointer typed. AI is the original
153     // allocation instruction, also pointer typed. Thus, cast to use is BitCast.
154     Value *NewCast = AllocaBuilder.CreateBitCast(New, AI.getType(), "tmpcast");
155     replaceInstUsesWith(AI, NewCast);
156   }
157   return replaceInstUsesWith(CI, New);
158 }
159 
160 /// Given an expression that CanEvaluateTruncated or CanEvaluateSExtd returns
161 /// true for, actually insert the code to evaluate the expression.
EvaluateInDifferentType(Value * V,Type * Ty,bool isSigned)162 Value *InstCombiner::EvaluateInDifferentType(Value *V, Type *Ty,
163                                              bool isSigned) {
164   if (Constant *C = dyn_cast<Constant>(V)) {
165     C = ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/);
166     // If we got a constantexpr back, try to simplify it with DL info.
167     if (Constant *FoldedC = ConstantFoldConstant(C, DL, &TLI))
168       C = FoldedC;
169     return C;
170   }
171 
172   // Otherwise, it must be an instruction.
173   Instruction *I = cast<Instruction>(V);
174   Instruction *Res = nullptr;
175   unsigned Opc = I->getOpcode();
176   switch (Opc) {
177   case Instruction::Add:
178   case Instruction::Sub:
179   case Instruction::Mul:
180   case Instruction::And:
181   case Instruction::Or:
182   case Instruction::Xor:
183   case Instruction::AShr:
184   case Instruction::LShr:
185   case Instruction::Shl:
186   case Instruction::UDiv:
187   case Instruction::URem: {
188     Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
189     Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
190     Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS);
191     break;
192   }
193   case Instruction::Trunc:
194   case Instruction::ZExt:
195   case Instruction::SExt:
196     // If the source type of the cast is the type we're trying for then we can
197     // just return the source.  There's no need to insert it because it is not
198     // new.
199     if (I->getOperand(0)->getType() == Ty)
200       return I->getOperand(0);
201 
202     // Otherwise, must be the same type of cast, so just reinsert a new one.
203     // This also handles the case of zext(trunc(x)) -> zext(x).
204     Res = CastInst::CreateIntegerCast(I->getOperand(0), Ty,
205                                       Opc == Instruction::SExt);
206     break;
207   case Instruction::Select: {
208     Value *True = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
209     Value *False = EvaluateInDifferentType(I->getOperand(2), Ty, isSigned);
210     Res = SelectInst::Create(I->getOperand(0), True, False);
211     break;
212   }
213   case Instruction::PHI: {
214     PHINode *OPN = cast<PHINode>(I);
215     PHINode *NPN = PHINode::Create(Ty, OPN->getNumIncomingValues());
216     for (unsigned i = 0, e = OPN->getNumIncomingValues(); i != e; ++i) {
217       Value *V =
218           EvaluateInDifferentType(OPN->getIncomingValue(i), Ty, isSigned);
219       NPN->addIncoming(V, OPN->getIncomingBlock(i));
220     }
221     Res = NPN;
222     break;
223   }
224   default:
225     // TODO: Can handle more cases here.
226     llvm_unreachable("Unreachable!");
227   }
228 
229   Res->takeName(I);
230   return InsertNewInstWith(Res, *I);
231 }
232 
isEliminableCastPair(const CastInst * CI1,const CastInst * CI2)233 Instruction::CastOps InstCombiner::isEliminableCastPair(const CastInst *CI1,
234                                                         const CastInst *CI2) {
235   Type *SrcTy = CI1->getSrcTy();
236   Type *MidTy = CI1->getDestTy();
237   Type *DstTy = CI2->getDestTy();
238 
239   Instruction::CastOps firstOp = CI1->getOpcode();
240   Instruction::CastOps secondOp = CI2->getOpcode();
241   Type *SrcIntPtrTy =
242       SrcTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(SrcTy) : nullptr;
243   Type *MidIntPtrTy =
244       MidTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(MidTy) : nullptr;
245   Type *DstIntPtrTy =
246       DstTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(DstTy) : nullptr;
247   unsigned Res = CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy,
248                                                 DstTy, SrcIntPtrTy, MidIntPtrTy,
249                                                 DstIntPtrTy);
250 
251   // We don't want to form an inttoptr or ptrtoint that converts to an integer
252   // type that differs from the pointer size.
253   if ((Res == Instruction::IntToPtr && SrcTy != DstIntPtrTy) ||
254       (Res == Instruction::PtrToInt && DstTy != SrcIntPtrTy))
255     Res = 0;
256 
257   return Instruction::CastOps(Res);
258 }
259 
260 /// Implement the transforms common to all CastInst visitors.
commonCastTransforms(CastInst & CI)261 Instruction *InstCombiner::commonCastTransforms(CastInst &CI) {
262   Value *Src = CI.getOperand(0);
263 
264   // Try to eliminate a cast of a cast.
265   if (auto *CSrc = dyn_cast<CastInst>(Src)) {   // A->B->C cast
266     if (Instruction::CastOps NewOpc = isEliminableCastPair(CSrc, &CI)) {
267       // The first cast (CSrc) is eliminable so we need to fix up or replace
268       // the second cast (CI). CSrc will then have a good chance of being dead.
269       auto *Ty = CI.getType();
270       auto *Res = CastInst::Create(NewOpc, CSrc->getOperand(0), Ty);
271       // Point debug users of the dying cast to the new one.
272       if (CSrc->hasOneUse())
273         replaceAllDbgUsesWith(*CSrc, *Res, CI, DT);
274       return Res;
275     }
276   }
277 
278   if (auto *Sel = dyn_cast<SelectInst>(Src)) {
279     // We are casting a select. Try to fold the cast into the select, but only
280     // if the select does not have a compare instruction with matching operand
281     // types. Creating a select with operands that are different sizes than its
282     // condition may inhibit other folds and lead to worse codegen.
283     auto *Cmp = dyn_cast<CmpInst>(Sel->getCondition());
284     if (!Cmp || Cmp->getOperand(0)->getType() != Sel->getType())
285       if (Instruction *NV = FoldOpIntoSelect(CI, Sel)) {
286         replaceAllDbgUsesWith(*Sel, *NV, CI, DT);
287         return NV;
288       }
289   }
290 
291   // If we are casting a PHI, then fold the cast into the PHI.
292   if (auto *PN = dyn_cast<PHINode>(Src)) {
293     // Don't do this if it would create a PHI node with an illegal type from a
294     // legal type.
295     if (!Src->getType()->isIntegerTy() || !CI.getType()->isIntegerTy() ||
296         shouldChangeType(CI.getType(), Src->getType()))
297       if (Instruction *NV = foldOpIntoPhi(CI, PN))
298         return NV;
299   }
300 
301   return nullptr;
302 }
303 
304 /// Constants and extensions/truncates from the destination type are always
305 /// free to be evaluated in that type. This is a helper for canEvaluate*.
canAlwaysEvaluateInType(Value * V,Type * Ty)306 static bool canAlwaysEvaluateInType(Value *V, Type *Ty) {
307   if (isa<Constant>(V))
308     return true;
309   Value *X;
310   if ((match(V, m_ZExtOrSExt(m_Value(X))) || match(V, m_Trunc(m_Value(X)))) &&
311       X->getType() == Ty)
312     return true;
313 
314   return false;
315 }
316 
317 /// Filter out values that we can not evaluate in the destination type for free.
318 /// This is a helper for canEvaluate*.
canNotEvaluateInType(Value * V,Type * Ty)319 static bool canNotEvaluateInType(Value *V, Type *Ty) {
320   assert(!isa<Constant>(V) && "Constant should already be handled.");
321   if (!isa<Instruction>(V))
322     return true;
323   // We don't extend or shrink something that has multiple uses --  doing so
324   // would require duplicating the instruction which isn't profitable.
325   if (!V->hasOneUse())
326     return true;
327 
328   return false;
329 }
330 
331 /// Return true if we can evaluate the specified expression tree as type Ty
332 /// instead of its larger type, and arrive with the same value.
333 /// This is used by code that tries to eliminate truncates.
334 ///
335 /// Ty will always be a type smaller than V.  We should return true if trunc(V)
336 /// can be computed by computing V in the smaller type.  If V is an instruction,
337 /// then trunc(inst(x,y)) can be computed as inst(trunc(x),trunc(y)), which only
338 /// makes sense if x and y can be efficiently truncated.
339 ///
340 /// This function works on both vectors and scalars.
341 ///
canEvaluateTruncated(Value * V,Type * Ty,InstCombiner & IC,Instruction * CxtI)342 static bool canEvaluateTruncated(Value *V, Type *Ty, InstCombiner &IC,
343                                  Instruction *CxtI) {
344   if (canAlwaysEvaluateInType(V, Ty))
345     return true;
346   if (canNotEvaluateInType(V, Ty))
347     return false;
348 
349   auto *I = cast<Instruction>(V);
350   Type *OrigTy = V->getType();
351   switch (I->getOpcode()) {
352   case Instruction::Add:
353   case Instruction::Sub:
354   case Instruction::Mul:
355   case Instruction::And:
356   case Instruction::Or:
357   case Instruction::Xor:
358     // These operators can all arbitrarily be extended or truncated.
359     return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI) &&
360            canEvaluateTruncated(I->getOperand(1), Ty, IC, CxtI);
361 
362   case Instruction::UDiv:
363   case Instruction::URem: {
364     // UDiv and URem can be truncated if all the truncated bits are zero.
365     uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
366     uint32_t BitWidth = Ty->getScalarSizeInBits();
367     assert(BitWidth < OrigBitWidth && "Unexpected bitwidths!");
368     APInt Mask = APInt::getBitsSetFrom(OrigBitWidth, BitWidth);
369     if (IC.MaskedValueIsZero(I->getOperand(0), Mask, 0, CxtI) &&
370         IC.MaskedValueIsZero(I->getOperand(1), Mask, 0, CxtI)) {
371       return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI) &&
372              canEvaluateTruncated(I->getOperand(1), Ty, IC, CxtI);
373     }
374     break;
375   }
376   case Instruction::Shl: {
377     // If we are truncating the result of this SHL, and if it's a shift of a
378     // constant amount, we can always perform a SHL in a smaller type.
379     const APInt *Amt;
380     if (match(I->getOperand(1), m_APInt(Amt))) {
381       uint32_t BitWidth = Ty->getScalarSizeInBits();
382       if (Amt->getLimitedValue(BitWidth) < BitWidth)
383         return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI);
384     }
385     break;
386   }
387   case Instruction::LShr: {
388     // If this is a truncate of a logical shr, we can truncate it to a smaller
389     // lshr iff we know that the bits we would otherwise be shifting in are
390     // already zeros.
391     const APInt *Amt;
392     if (match(I->getOperand(1), m_APInt(Amt))) {
393       uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
394       uint32_t BitWidth = Ty->getScalarSizeInBits();
395       if (Amt->getLimitedValue(BitWidth) < BitWidth &&
396           IC.MaskedValueIsZero(I->getOperand(0),
397             APInt::getBitsSetFrom(OrigBitWidth, BitWidth), 0, CxtI)) {
398         return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI);
399       }
400     }
401     break;
402   }
403   case Instruction::AShr: {
404     // If this is a truncate of an arithmetic shr, we can truncate it to a
405     // smaller ashr iff we know that all the bits from the sign bit of the
406     // original type and the sign bit of the truncate type are similar.
407     // TODO: It is enough to check that the bits we would be shifting in are
408     //       similar to sign bit of the truncate type.
409     const APInt *Amt;
410     if (match(I->getOperand(1), m_APInt(Amt))) {
411       uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
412       uint32_t BitWidth = Ty->getScalarSizeInBits();
413       if (Amt->getLimitedValue(BitWidth) < BitWidth &&
414           OrigBitWidth - BitWidth <
415               IC.ComputeNumSignBits(I->getOperand(0), 0, CxtI))
416         return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI);
417     }
418     break;
419   }
420   case Instruction::Trunc:
421     // trunc(trunc(x)) -> trunc(x)
422     return true;
423   case Instruction::ZExt:
424   case Instruction::SExt:
425     // trunc(ext(x)) -> ext(x) if the source type is smaller than the new dest
426     // trunc(ext(x)) -> trunc(x) if the source type is larger than the new dest
427     return true;
428   case Instruction::Select: {
429     SelectInst *SI = cast<SelectInst>(I);
430     return canEvaluateTruncated(SI->getTrueValue(), Ty, IC, CxtI) &&
431            canEvaluateTruncated(SI->getFalseValue(), Ty, IC, CxtI);
432   }
433   case Instruction::PHI: {
434     // We can change a phi if we can change all operands.  Note that we never
435     // get into trouble with cyclic PHIs here because we only consider
436     // instructions with a single use.
437     PHINode *PN = cast<PHINode>(I);
438     for (Value *IncValue : PN->incoming_values())
439       if (!canEvaluateTruncated(IncValue, Ty, IC, CxtI))
440         return false;
441     return true;
442   }
443   default:
444     // TODO: Can handle more cases here.
445     break;
446   }
447 
448   return false;
449 }
450 
451 /// Given a vector that is bitcast to an integer, optionally logically
452 /// right-shifted, and truncated, convert it to an extractelement.
453 /// Example (big endian):
454 ///   trunc (lshr (bitcast <4 x i32> %X to i128), 32) to i32
455 ///   --->
456 ///   extractelement <4 x i32> %X, 1
foldVecTruncToExtElt(TruncInst & Trunc,InstCombiner & IC)457 static Instruction *foldVecTruncToExtElt(TruncInst &Trunc, InstCombiner &IC) {
458   Value *TruncOp = Trunc.getOperand(0);
459   Type *DestType = Trunc.getType();
460   if (!TruncOp->hasOneUse() || !isa<IntegerType>(DestType))
461     return nullptr;
462 
463   Value *VecInput = nullptr;
464   ConstantInt *ShiftVal = nullptr;
465   if (!match(TruncOp, m_CombineOr(m_BitCast(m_Value(VecInput)),
466                                   m_LShr(m_BitCast(m_Value(VecInput)),
467                                          m_ConstantInt(ShiftVal)))) ||
468       !isa<VectorType>(VecInput->getType()))
469     return nullptr;
470 
471   VectorType *VecType = cast<VectorType>(VecInput->getType());
472   unsigned VecWidth = VecType->getPrimitiveSizeInBits();
473   unsigned DestWidth = DestType->getPrimitiveSizeInBits();
474   unsigned ShiftAmount = ShiftVal ? ShiftVal->getZExtValue() : 0;
475 
476   if ((VecWidth % DestWidth != 0) || (ShiftAmount % DestWidth != 0))
477     return nullptr;
478 
479   // If the element type of the vector doesn't match the result type,
480   // bitcast it to a vector type that we can extract from.
481   unsigned NumVecElts = VecWidth / DestWidth;
482   if (VecType->getElementType() != DestType) {
483     VecType = VectorType::get(DestType, NumVecElts);
484     VecInput = IC.Builder.CreateBitCast(VecInput, VecType, "bc");
485   }
486 
487   unsigned Elt = ShiftAmount / DestWidth;
488   if (IC.getDataLayout().isBigEndian())
489     Elt = NumVecElts - 1 - Elt;
490 
491   return ExtractElementInst::Create(VecInput, IC.Builder.getInt32(Elt));
492 }
493 
494 /// Rotate left/right may occur in a wider type than necessary because of type
495 /// promotion rules. Try to narrow all of the component instructions.
narrowRotate(TruncInst & Trunc)496 Instruction *InstCombiner::narrowRotate(TruncInst &Trunc) {
497   assert((isa<VectorType>(Trunc.getSrcTy()) ||
498           shouldChangeType(Trunc.getSrcTy(), Trunc.getType())) &&
499          "Don't narrow to an illegal scalar type");
500 
501   // First, find an or'd pair of opposite shifts with the same shifted operand:
502   // trunc (or (lshr ShVal, ShAmt0), (shl ShVal, ShAmt1))
503   Value *Or0, *Or1;
504   if (!match(Trunc.getOperand(0), m_OneUse(m_Or(m_Value(Or0), m_Value(Or1)))))
505     return nullptr;
506 
507   Value *ShVal, *ShAmt0, *ShAmt1;
508   if (!match(Or0, m_OneUse(m_LogicalShift(m_Value(ShVal), m_Value(ShAmt0)))) ||
509       !match(Or1, m_OneUse(m_LogicalShift(m_Specific(ShVal), m_Value(ShAmt1)))))
510     return nullptr;
511 
512   auto ShiftOpcode0 = cast<BinaryOperator>(Or0)->getOpcode();
513   auto ShiftOpcode1 = cast<BinaryOperator>(Or1)->getOpcode();
514   if (ShiftOpcode0 == ShiftOpcode1)
515     return nullptr;
516 
517   // The shift amounts must add up to the narrow bit width.
518   Value *ShAmt;
519   bool SubIsOnLHS;
520   Type *DestTy = Trunc.getType();
521   unsigned NarrowWidth = DestTy->getScalarSizeInBits();
522   if (match(ShAmt0,
523             m_OneUse(m_Sub(m_SpecificInt(NarrowWidth), m_Specific(ShAmt1))))) {
524     ShAmt = ShAmt1;
525     SubIsOnLHS = true;
526   } else if (match(ShAmt1, m_OneUse(m_Sub(m_SpecificInt(NarrowWidth),
527                                           m_Specific(ShAmt0))))) {
528     ShAmt = ShAmt0;
529     SubIsOnLHS = false;
530   } else {
531     return nullptr;
532   }
533 
534   // The shifted value must have high zeros in the wide type. Typically, this
535   // will be a zext, but it could also be the result of an 'and' or 'shift'.
536   unsigned WideWidth = Trunc.getSrcTy()->getScalarSizeInBits();
537   APInt HiBitMask = APInt::getHighBitsSet(WideWidth, WideWidth - NarrowWidth);
538   if (!MaskedValueIsZero(ShVal, HiBitMask, 0, &Trunc))
539     return nullptr;
540 
541   // We have an unnecessarily wide rotate!
542   // trunc (or (lshr ShVal, ShAmt), (shl ShVal, BitWidth - ShAmt))
543   // Narrow it down to eliminate the zext/trunc:
544   // or (lshr trunc(ShVal), ShAmt0'), (shl trunc(ShVal), ShAmt1')
545   Value *NarrowShAmt = Builder.CreateTrunc(ShAmt, DestTy);
546   Value *NegShAmt = Builder.CreateNeg(NarrowShAmt);
547 
548   // Mask both shift amounts to ensure there's no UB from oversized shifts.
549   Constant *MaskC = ConstantInt::get(DestTy, NarrowWidth - 1);
550   Value *MaskedShAmt = Builder.CreateAnd(NarrowShAmt, MaskC);
551   Value *MaskedNegShAmt = Builder.CreateAnd(NegShAmt, MaskC);
552 
553   // Truncate the original value and use narrow ops.
554   Value *X = Builder.CreateTrunc(ShVal, DestTy);
555   Value *NarrowShAmt0 = SubIsOnLHS ? MaskedNegShAmt : MaskedShAmt;
556   Value *NarrowShAmt1 = SubIsOnLHS ? MaskedShAmt : MaskedNegShAmt;
557   Value *NarrowSh0 = Builder.CreateBinOp(ShiftOpcode0, X, NarrowShAmt0);
558   Value *NarrowSh1 = Builder.CreateBinOp(ShiftOpcode1, X, NarrowShAmt1);
559   return BinaryOperator::CreateOr(NarrowSh0, NarrowSh1);
560 }
561 
562 /// Try to narrow the width of math or bitwise logic instructions by pulling a
563 /// truncate ahead of binary operators.
564 /// TODO: Transforms for truncated shifts should be moved into here.
narrowBinOp(TruncInst & Trunc)565 Instruction *InstCombiner::narrowBinOp(TruncInst &Trunc) {
566   Type *SrcTy = Trunc.getSrcTy();
567   Type *DestTy = Trunc.getType();
568   if (!isa<VectorType>(SrcTy) && !shouldChangeType(SrcTy, DestTy))
569     return nullptr;
570 
571   BinaryOperator *BinOp;
572   if (!match(Trunc.getOperand(0), m_OneUse(m_BinOp(BinOp))))
573     return nullptr;
574 
575   Value *BinOp0 = BinOp->getOperand(0);
576   Value *BinOp1 = BinOp->getOperand(1);
577   switch (BinOp->getOpcode()) {
578   case Instruction::And:
579   case Instruction::Or:
580   case Instruction::Xor:
581   case Instruction::Add:
582   case Instruction::Sub:
583   case Instruction::Mul: {
584     Constant *C;
585     if (match(BinOp0, m_Constant(C))) {
586       // trunc (binop C, X) --> binop (trunc C', X)
587       Constant *NarrowC = ConstantExpr::getTrunc(C, DestTy);
588       Value *TruncX = Builder.CreateTrunc(BinOp1, DestTy);
589       return BinaryOperator::Create(BinOp->getOpcode(), NarrowC, TruncX);
590     }
591     if (match(BinOp1, m_Constant(C))) {
592       // trunc (binop X, C) --> binop (trunc X, C')
593       Constant *NarrowC = ConstantExpr::getTrunc(C, DestTy);
594       Value *TruncX = Builder.CreateTrunc(BinOp0, DestTy);
595       return BinaryOperator::Create(BinOp->getOpcode(), TruncX, NarrowC);
596     }
597     Value *X;
598     if (match(BinOp0, m_ZExtOrSExt(m_Value(X))) && X->getType() == DestTy) {
599       // trunc (binop (ext X), Y) --> binop X, (trunc Y)
600       Value *NarrowOp1 = Builder.CreateTrunc(BinOp1, DestTy);
601       return BinaryOperator::Create(BinOp->getOpcode(), X, NarrowOp1);
602     }
603     if (match(BinOp1, m_ZExtOrSExt(m_Value(X))) && X->getType() == DestTy) {
604       // trunc (binop Y, (ext X)) --> binop (trunc Y), X
605       Value *NarrowOp0 = Builder.CreateTrunc(BinOp0, DestTy);
606       return BinaryOperator::Create(BinOp->getOpcode(), NarrowOp0, X);
607     }
608     break;
609   }
610 
611   default: break;
612   }
613 
614   if (Instruction *NarrowOr = narrowRotate(Trunc))
615     return NarrowOr;
616 
617   return nullptr;
618 }
619 
620 /// Try to narrow the width of a splat shuffle. This could be generalized to any
621 /// shuffle with a constant operand, but we limit the transform to avoid
622 /// creating a shuffle type that targets may not be able to lower effectively.
shrinkSplatShuffle(TruncInst & Trunc,InstCombiner::BuilderTy & Builder)623 static Instruction *shrinkSplatShuffle(TruncInst &Trunc,
624                                        InstCombiner::BuilderTy &Builder) {
625   auto *Shuf = dyn_cast<ShuffleVectorInst>(Trunc.getOperand(0));
626   if (Shuf && Shuf->hasOneUse() && isa<UndefValue>(Shuf->getOperand(1)) &&
627       Shuf->getMask()->getSplatValue() &&
628       Shuf->getType() == Shuf->getOperand(0)->getType()) {
629     // trunc (shuf X, Undef, SplatMask) --> shuf (trunc X), Undef, SplatMask
630     Constant *NarrowUndef = UndefValue::get(Trunc.getType());
631     Value *NarrowOp = Builder.CreateTrunc(Shuf->getOperand(0), Trunc.getType());
632     return new ShuffleVectorInst(NarrowOp, NarrowUndef, Shuf->getMask());
633   }
634 
635   return nullptr;
636 }
637 
638 /// Try to narrow the width of an insert element. This could be generalized for
639 /// any vector constant, but we limit the transform to insertion into undef to
640 /// avoid potential backend problems from unsupported insertion widths. This
641 /// could also be extended to handle the case of inserting a scalar constant
642 /// into a vector variable.
shrinkInsertElt(CastInst & Trunc,InstCombiner::BuilderTy & Builder)643 static Instruction *shrinkInsertElt(CastInst &Trunc,
644                                     InstCombiner::BuilderTy &Builder) {
645   Instruction::CastOps Opcode = Trunc.getOpcode();
646   assert((Opcode == Instruction::Trunc || Opcode == Instruction::FPTrunc) &&
647          "Unexpected instruction for shrinking");
648 
649   auto *InsElt = dyn_cast<InsertElementInst>(Trunc.getOperand(0));
650   if (!InsElt || !InsElt->hasOneUse())
651     return nullptr;
652 
653   Type *DestTy = Trunc.getType();
654   Type *DestScalarTy = DestTy->getScalarType();
655   Value *VecOp = InsElt->getOperand(0);
656   Value *ScalarOp = InsElt->getOperand(1);
657   Value *Index = InsElt->getOperand(2);
658 
659   if (isa<UndefValue>(VecOp)) {
660     // trunc   (inselt undef, X, Index) --> inselt undef,   (trunc X), Index
661     // fptrunc (inselt undef, X, Index) --> inselt undef, (fptrunc X), Index
662     UndefValue *NarrowUndef = UndefValue::get(DestTy);
663     Value *NarrowOp = Builder.CreateCast(Opcode, ScalarOp, DestScalarTy);
664     return InsertElementInst::Create(NarrowUndef, NarrowOp, Index);
665   }
666 
667   return nullptr;
668 }
669 
visitTrunc(TruncInst & CI)670 Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
671   if (Instruction *Result = commonCastTransforms(CI))
672     return Result;
673 
674   Value *Src = CI.getOperand(0);
675   Type *DestTy = CI.getType(), *SrcTy = Src->getType();
676 
677   // Attempt to truncate the entire input expression tree to the destination
678   // type.   Only do this if the dest type is a simple type, don't convert the
679   // expression tree to something weird like i93 unless the source is also
680   // strange.
681   if ((DestTy->isVectorTy() || shouldChangeType(SrcTy, DestTy)) &&
682       canEvaluateTruncated(Src, DestTy, *this, &CI)) {
683 
684     // If this cast is a truncate, evaluting in a different type always
685     // eliminates the cast, so it is always a win.
686     LLVM_DEBUG(
687         dbgs() << "ICE: EvaluateInDifferentType converting expression type"
688                   " to avoid cast: "
689                << CI << '\n');
690     Value *Res = EvaluateInDifferentType(Src, DestTy, false);
691     assert(Res->getType() == DestTy);
692     return replaceInstUsesWith(CI, Res);
693   }
694 
695   // Test if the trunc is the user of a select which is part of a
696   // minimum or maximum operation. If so, don't do any more simplification.
697   // Even simplifying demanded bits can break the canonical form of a
698   // min/max.
699   Value *LHS, *RHS;
700   if (SelectInst *SI = dyn_cast<SelectInst>(CI.getOperand(0)))
701     if (matchSelectPattern(SI, LHS, RHS).Flavor != SPF_UNKNOWN)
702       return nullptr;
703 
704   // See if we can simplify any instructions used by the input whose sole
705   // purpose is to compute bits we don't care about.
706   if (SimplifyDemandedInstructionBits(CI))
707     return &CI;
708 
709   // Canonicalize trunc x to i1 -> (icmp ne (and x, 1), 0), likewise for vector.
710   if (DestTy->getScalarSizeInBits() == 1) {
711     Constant *One = ConstantInt::get(SrcTy, 1);
712     Src = Builder.CreateAnd(Src, One);
713     Value *Zero = Constant::getNullValue(Src->getType());
714     return new ICmpInst(ICmpInst::ICMP_NE, Src, Zero);
715   }
716 
717   // FIXME: Maybe combine the next two transforms to handle the no cast case
718   // more efficiently. Support vector types. Cleanup code by using m_OneUse.
719 
720   // Transform trunc(lshr (zext A), Cst) to eliminate one type conversion.
721   Value *A = nullptr; ConstantInt *Cst = nullptr;
722   if (Src->hasOneUse() &&
723       match(Src, m_LShr(m_ZExt(m_Value(A)), m_ConstantInt(Cst)))) {
724     // We have three types to worry about here, the type of A, the source of
725     // the truncate (MidSize), and the destination of the truncate. We know that
726     // ASize < MidSize   and MidSize > ResultSize, but don't know the relation
727     // between ASize and ResultSize.
728     unsigned ASize = A->getType()->getPrimitiveSizeInBits();
729 
730     // If the shift amount is larger than the size of A, then the result is
731     // known to be zero because all the input bits got shifted out.
732     if (Cst->getZExtValue() >= ASize)
733       return replaceInstUsesWith(CI, Constant::getNullValue(DestTy));
734 
735     // Since we're doing an lshr and a zero extend, and know that the shift
736     // amount is smaller than ASize, it is always safe to do the shift in A's
737     // type, then zero extend or truncate to the result.
738     Value *Shift = Builder.CreateLShr(A, Cst->getZExtValue());
739     Shift->takeName(Src);
740     return CastInst::CreateIntegerCast(Shift, DestTy, false);
741   }
742 
743   // FIXME: We should canonicalize to zext/trunc and remove this transform.
744   // Transform trunc(lshr (sext A), Cst) to ashr A, Cst to eliminate type
745   // conversion.
746   // It works because bits coming from sign extension have the same value as
747   // the sign bit of the original value; performing ashr instead of lshr
748   // generates bits of the same value as the sign bit.
749   if (Src->hasOneUse() &&
750       match(Src, m_LShr(m_SExt(m_Value(A)), m_ConstantInt(Cst)))) {
751     Value *SExt = cast<Instruction>(Src)->getOperand(0);
752     const unsigned SExtSize = SExt->getType()->getPrimitiveSizeInBits();
753     const unsigned ASize = A->getType()->getPrimitiveSizeInBits();
754     const unsigned CISize = CI.getType()->getPrimitiveSizeInBits();
755     const unsigned MaxAmt = SExtSize - std::max(CISize, ASize);
756     unsigned ShiftAmt = Cst->getZExtValue();
757 
758     // This optimization can be only performed when zero bits generated by
759     // the original lshr aren't pulled into the value after truncation, so we
760     // can only shift by values no larger than the number of extension bits.
761     // FIXME: Instead of bailing when the shift is too large, use and to clear
762     // the extra bits.
763     if (ShiftAmt <= MaxAmt) {
764       if (CISize == ASize)
765         return BinaryOperator::CreateAShr(A, ConstantInt::get(CI.getType(),
766                                           std::min(ShiftAmt, ASize - 1)));
767       if (SExt->hasOneUse()) {
768         Value *Shift = Builder.CreateAShr(A, std::min(ShiftAmt, ASize - 1));
769         Shift->takeName(Src);
770         return CastInst::CreateIntegerCast(Shift, CI.getType(), true);
771       }
772     }
773   }
774 
775   if (Instruction *I = narrowBinOp(CI))
776     return I;
777 
778   if (Instruction *I = shrinkSplatShuffle(CI, Builder))
779     return I;
780 
781   if (Instruction *I = shrinkInsertElt(CI, Builder))
782     return I;
783 
784   if (Src->hasOneUse() && isa<IntegerType>(SrcTy) &&
785       shouldChangeType(SrcTy, DestTy)) {
786     // Transform "trunc (shl X, cst)" -> "shl (trunc X), cst" so long as the
787     // dest type is native and cst < dest size.
788     if (match(Src, m_Shl(m_Value(A), m_ConstantInt(Cst))) &&
789         !match(A, m_Shr(m_Value(), m_Constant()))) {
790       // Skip shifts of shift by constants. It undoes a combine in
791       // FoldShiftByConstant and is the extend in reg pattern.
792       const unsigned DestSize = DestTy->getScalarSizeInBits();
793       if (Cst->getValue().ult(DestSize)) {
794         Value *NewTrunc = Builder.CreateTrunc(A, DestTy, A->getName() + ".tr");
795 
796         return BinaryOperator::Create(
797           Instruction::Shl, NewTrunc,
798           ConstantInt::get(DestTy, Cst->getValue().trunc(DestSize)));
799       }
800     }
801   }
802 
803   if (Instruction *I = foldVecTruncToExtElt(CI, *this))
804     return I;
805 
806   return nullptr;
807 }
808 
transformZExtICmp(ICmpInst * ICI,ZExtInst & CI,bool DoTransform)809 Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, ZExtInst &CI,
810                                              bool DoTransform) {
811   // If we are just checking for a icmp eq of a single bit and zext'ing it
812   // to an integer, then shift the bit to the appropriate place and then
813   // cast to integer to avoid the comparison.
814   const APInt *Op1CV;
815   if (match(ICI->getOperand(1), m_APInt(Op1CV))) {
816 
817     // zext (x <s  0) to i32 --> x>>u31      true if signbit set.
818     // zext (x >s -1) to i32 --> (x>>u31)^1  true if signbit clear.
819     if ((ICI->getPredicate() == ICmpInst::ICMP_SLT && Op1CV->isNullValue()) ||
820         (ICI->getPredicate() == ICmpInst::ICMP_SGT && Op1CV->isAllOnesValue())) {
821       if (!DoTransform) return ICI;
822 
823       Value *In = ICI->getOperand(0);
824       Value *Sh = ConstantInt::get(In->getType(),
825                                    In->getType()->getScalarSizeInBits() - 1);
826       In = Builder.CreateLShr(In, Sh, In->getName() + ".lobit");
827       if (In->getType() != CI.getType())
828         In = Builder.CreateIntCast(In, CI.getType(), false /*ZExt*/);
829 
830       if (ICI->getPredicate() == ICmpInst::ICMP_SGT) {
831         Constant *One = ConstantInt::get(In->getType(), 1);
832         In = Builder.CreateXor(In, One, In->getName() + ".not");
833       }
834 
835       return replaceInstUsesWith(CI, In);
836     }
837 
838     // zext (X == 0) to i32 --> X^1      iff X has only the low bit set.
839     // zext (X == 0) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
840     // zext (X == 1) to i32 --> X        iff X has only the low bit set.
841     // zext (X == 2) to i32 --> X>>1     iff X has only the 2nd bit set.
842     // zext (X != 0) to i32 --> X        iff X has only the low bit set.
843     // zext (X != 0) to i32 --> X>>1     iff X has only the 2nd bit set.
844     // zext (X != 1) to i32 --> X^1      iff X has only the low bit set.
845     // zext (X != 2) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
846     if ((Op1CV->isNullValue() || Op1CV->isPowerOf2()) &&
847         // This only works for EQ and NE
848         ICI->isEquality()) {
849       // If Op1C some other power of two, convert:
850       KnownBits Known = computeKnownBits(ICI->getOperand(0), 0, &CI);
851 
852       APInt KnownZeroMask(~Known.Zero);
853       if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1?
854         if (!DoTransform) return ICI;
855 
856         bool isNE = ICI->getPredicate() == ICmpInst::ICMP_NE;
857         if (!Op1CV->isNullValue() && (*Op1CV != KnownZeroMask)) {
858           // (X&4) == 2 --> false
859           // (X&4) != 2 --> true
860           Constant *Res = ConstantInt::get(CI.getType(), isNE);
861           return replaceInstUsesWith(CI, Res);
862         }
863 
864         uint32_t ShAmt = KnownZeroMask.logBase2();
865         Value *In = ICI->getOperand(0);
866         if (ShAmt) {
867           // Perform a logical shr by shiftamt.
868           // Insert the shift to put the result in the low bit.
869           In = Builder.CreateLShr(In, ConstantInt::get(In->getType(), ShAmt),
870                                   In->getName() + ".lobit");
871         }
872 
873         if (!Op1CV->isNullValue() == isNE) { // Toggle the low bit.
874           Constant *One = ConstantInt::get(In->getType(), 1);
875           In = Builder.CreateXor(In, One);
876         }
877 
878         if (CI.getType() == In->getType())
879           return replaceInstUsesWith(CI, In);
880 
881         Value *IntCast = Builder.CreateIntCast(In, CI.getType(), false);
882         return replaceInstUsesWith(CI, IntCast);
883       }
884     }
885   }
886 
887   // icmp ne A, B is equal to xor A, B when A and B only really have one bit.
888   // It is also profitable to transform icmp eq into not(xor(A, B)) because that
889   // may lead to additional simplifications.
890   if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) {
891     if (IntegerType *ITy = dyn_cast<IntegerType>(CI.getType())) {
892       Value *LHS = ICI->getOperand(0);
893       Value *RHS = ICI->getOperand(1);
894 
895       KnownBits KnownLHS = computeKnownBits(LHS, 0, &CI);
896       KnownBits KnownRHS = computeKnownBits(RHS, 0, &CI);
897 
898       if (KnownLHS.Zero == KnownRHS.Zero && KnownLHS.One == KnownRHS.One) {
899         APInt KnownBits = KnownLHS.Zero | KnownLHS.One;
900         APInt UnknownBit = ~KnownBits;
901         if (UnknownBit.countPopulation() == 1) {
902           if (!DoTransform) return ICI;
903 
904           Value *Result = Builder.CreateXor(LHS, RHS);
905 
906           // Mask off any bits that are set and won't be shifted away.
907           if (KnownLHS.One.uge(UnknownBit))
908             Result = Builder.CreateAnd(Result,
909                                         ConstantInt::get(ITy, UnknownBit));
910 
911           // Shift the bit we're testing down to the lsb.
912           Result = Builder.CreateLShr(
913                Result, ConstantInt::get(ITy, UnknownBit.countTrailingZeros()));
914 
915           if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
916             Result = Builder.CreateXor(Result, ConstantInt::get(ITy, 1));
917           Result->takeName(ICI);
918           return replaceInstUsesWith(CI, Result);
919         }
920       }
921     }
922   }
923 
924   return nullptr;
925 }
926 
927 /// Determine if the specified value can be computed in the specified wider type
928 /// and produce the same low bits. If not, return false.
929 ///
930 /// If this function returns true, it can also return a non-zero number of bits
931 /// (in BitsToClear) which indicates that the value it computes is correct for
932 /// the zero extend, but that the additional BitsToClear bits need to be zero'd
933 /// out.  For example, to promote something like:
934 ///
935 ///   %B = trunc i64 %A to i32
936 ///   %C = lshr i32 %B, 8
937 ///   %E = zext i32 %C to i64
938 ///
939 /// CanEvaluateZExtd for the 'lshr' will return true, and BitsToClear will be
940 /// set to 8 to indicate that the promoted value needs to have bits 24-31
941 /// cleared in addition to bits 32-63.  Since an 'and' will be generated to
942 /// clear the top bits anyway, doing this has no extra cost.
943 ///
944 /// This function works on both vectors and scalars.
canEvaluateZExtd(Value * V,Type * Ty,unsigned & BitsToClear,InstCombiner & IC,Instruction * CxtI)945 static bool canEvaluateZExtd(Value *V, Type *Ty, unsigned &BitsToClear,
946                              InstCombiner &IC, Instruction *CxtI) {
947   BitsToClear = 0;
948   if (canAlwaysEvaluateInType(V, Ty))
949     return true;
950   if (canNotEvaluateInType(V, Ty))
951     return false;
952 
953   auto *I = cast<Instruction>(V);
954   unsigned Tmp;
955   switch (I->getOpcode()) {
956   case Instruction::ZExt:  // zext(zext(x)) -> zext(x).
957   case Instruction::SExt:  // zext(sext(x)) -> sext(x).
958   case Instruction::Trunc: // zext(trunc(x)) -> trunc(x) or zext(x)
959     return true;
960   case Instruction::And:
961   case Instruction::Or:
962   case Instruction::Xor:
963   case Instruction::Add:
964   case Instruction::Sub:
965   case Instruction::Mul:
966     if (!canEvaluateZExtd(I->getOperand(0), Ty, BitsToClear, IC, CxtI) ||
967         !canEvaluateZExtd(I->getOperand(1), Ty, Tmp, IC, CxtI))
968       return false;
969     // These can all be promoted if neither operand has 'bits to clear'.
970     if (BitsToClear == 0 && Tmp == 0)
971       return true;
972 
973     // If the operation is an AND/OR/XOR and the bits to clear are zero in the
974     // other side, BitsToClear is ok.
975     if (Tmp == 0 && I->isBitwiseLogicOp()) {
976       // We use MaskedValueIsZero here for generality, but the case we care
977       // about the most is constant RHS.
978       unsigned VSize = V->getType()->getScalarSizeInBits();
979       if (IC.MaskedValueIsZero(I->getOperand(1),
980                                APInt::getHighBitsSet(VSize, BitsToClear),
981                                0, CxtI)) {
982         // If this is an And instruction and all of the BitsToClear are
983         // known to be zero we can reset BitsToClear.
984         if (I->getOpcode() == Instruction::And)
985           BitsToClear = 0;
986         return true;
987       }
988     }
989 
990     // Otherwise, we don't know how to analyze this BitsToClear case yet.
991     return false;
992 
993   case Instruction::Shl: {
994     // We can promote shl(x, cst) if we can promote x.  Since shl overwrites the
995     // upper bits we can reduce BitsToClear by the shift amount.
996     const APInt *Amt;
997     if (match(I->getOperand(1), m_APInt(Amt))) {
998       if (!canEvaluateZExtd(I->getOperand(0), Ty, BitsToClear, IC, CxtI))
999         return false;
1000       uint64_t ShiftAmt = Amt->getZExtValue();
1001       BitsToClear = ShiftAmt < BitsToClear ? BitsToClear - ShiftAmt : 0;
1002       return true;
1003     }
1004     return false;
1005   }
1006   case Instruction::LShr: {
1007     // We can promote lshr(x, cst) if we can promote x.  This requires the
1008     // ultimate 'and' to clear out the high zero bits we're clearing out though.
1009     const APInt *Amt;
1010     if (match(I->getOperand(1), m_APInt(Amt))) {
1011       if (!canEvaluateZExtd(I->getOperand(0), Ty, BitsToClear, IC, CxtI))
1012         return false;
1013       BitsToClear += Amt->getZExtValue();
1014       if (BitsToClear > V->getType()->getScalarSizeInBits())
1015         BitsToClear = V->getType()->getScalarSizeInBits();
1016       return true;
1017     }
1018     // Cannot promote variable LSHR.
1019     return false;
1020   }
1021   case Instruction::Select:
1022     if (!canEvaluateZExtd(I->getOperand(1), Ty, Tmp, IC, CxtI) ||
1023         !canEvaluateZExtd(I->getOperand(2), Ty, BitsToClear, IC, CxtI) ||
1024         // TODO: If important, we could handle the case when the BitsToClear are
1025         // known zero in the disagreeing side.
1026         Tmp != BitsToClear)
1027       return false;
1028     return true;
1029 
1030   case Instruction::PHI: {
1031     // We can change a phi if we can change all operands.  Note that we never
1032     // get into trouble with cyclic PHIs here because we only consider
1033     // instructions with a single use.
1034     PHINode *PN = cast<PHINode>(I);
1035     if (!canEvaluateZExtd(PN->getIncomingValue(0), Ty, BitsToClear, IC, CxtI))
1036       return false;
1037     for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
1038       if (!canEvaluateZExtd(PN->getIncomingValue(i), Ty, Tmp, IC, CxtI) ||
1039           // TODO: If important, we could handle the case when the BitsToClear
1040           // are known zero in the disagreeing input.
1041           Tmp != BitsToClear)
1042         return false;
1043     return true;
1044   }
1045   default:
1046     // TODO: Can handle more cases here.
1047     return false;
1048   }
1049 }
1050 
visitZExt(ZExtInst & CI)1051 Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
1052   // If this zero extend is only used by a truncate, let the truncate be
1053   // eliminated before we try to optimize this zext.
1054   if (CI.hasOneUse() && isa<TruncInst>(CI.user_back()))
1055     return nullptr;
1056 
1057   // If one of the common conversion will work, do it.
1058   if (Instruction *Result = commonCastTransforms(CI))
1059     return Result;
1060 
1061   Value *Src = CI.getOperand(0);
1062   Type *SrcTy = Src->getType(), *DestTy = CI.getType();
1063 
1064   // Attempt to extend the entire input expression tree to the destination
1065   // type.   Only do this if the dest type is a simple type, don't convert the
1066   // expression tree to something weird like i93 unless the source is also
1067   // strange.
1068   unsigned BitsToClear;
1069   if ((DestTy->isVectorTy() || shouldChangeType(SrcTy, DestTy)) &&
1070       canEvaluateZExtd(Src, DestTy, BitsToClear, *this, &CI)) {
1071     assert(BitsToClear <= SrcTy->getScalarSizeInBits() &&
1072            "Can't clear more bits than in SrcTy");
1073 
1074     // Okay, we can transform this!  Insert the new expression now.
1075     LLVM_DEBUG(
1076         dbgs() << "ICE: EvaluateInDifferentType converting expression type"
1077                   " to avoid zero extend: "
1078                << CI << '\n');
1079     Value *Res = EvaluateInDifferentType(Src, DestTy, false);
1080     assert(Res->getType() == DestTy);
1081 
1082     // Preserve debug values referring to Src if the zext is its last use.
1083     if (auto *SrcOp = dyn_cast<Instruction>(Src))
1084       if (SrcOp->hasOneUse())
1085         replaceAllDbgUsesWith(*SrcOp, *Res, CI, DT);
1086 
1087     uint32_t SrcBitsKept = SrcTy->getScalarSizeInBits()-BitsToClear;
1088     uint32_t DestBitSize = DestTy->getScalarSizeInBits();
1089 
1090     // If the high bits are already filled with zeros, just replace this
1091     // cast with the result.
1092     if (MaskedValueIsZero(Res,
1093                           APInt::getHighBitsSet(DestBitSize,
1094                                                 DestBitSize-SrcBitsKept),
1095                              0, &CI))
1096       return replaceInstUsesWith(CI, Res);
1097 
1098     // We need to emit an AND to clear the high bits.
1099     Constant *C = ConstantInt::get(Res->getType(),
1100                                APInt::getLowBitsSet(DestBitSize, SrcBitsKept));
1101     return BinaryOperator::CreateAnd(Res, C);
1102   }
1103 
1104   // If this is a TRUNC followed by a ZEXT then we are dealing with integral
1105   // types and if the sizes are just right we can convert this into a logical
1106   // 'and' which will be much cheaper than the pair of casts.
1107   if (TruncInst *CSrc = dyn_cast<TruncInst>(Src)) {   // A->B->C cast
1108     // TODO: Subsume this into EvaluateInDifferentType.
1109 
1110     // Get the sizes of the types involved.  We know that the intermediate type
1111     // will be smaller than A or C, but don't know the relation between A and C.
1112     Value *A = CSrc->getOperand(0);
1113     unsigned SrcSize = A->getType()->getScalarSizeInBits();
1114     unsigned MidSize = CSrc->getType()->getScalarSizeInBits();
1115     unsigned DstSize = CI.getType()->getScalarSizeInBits();
1116     // If we're actually extending zero bits, then if
1117     // SrcSize <  DstSize: zext(a & mask)
1118     // SrcSize == DstSize: a & mask
1119     // SrcSize  > DstSize: trunc(a) & mask
1120     if (SrcSize < DstSize) {
1121       APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
1122       Constant *AndConst = ConstantInt::get(A->getType(), AndValue);
1123       Value *And = Builder.CreateAnd(A, AndConst, CSrc->getName() + ".mask");
1124       return new ZExtInst(And, CI.getType());
1125     }
1126 
1127     if (SrcSize == DstSize) {
1128       APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
1129       return BinaryOperator::CreateAnd(A, ConstantInt::get(A->getType(),
1130                                                            AndValue));
1131     }
1132     if (SrcSize > DstSize) {
1133       Value *Trunc = Builder.CreateTrunc(A, CI.getType());
1134       APInt AndValue(APInt::getLowBitsSet(DstSize, MidSize));
1135       return BinaryOperator::CreateAnd(Trunc,
1136                                        ConstantInt::get(Trunc->getType(),
1137                                                         AndValue));
1138     }
1139   }
1140 
1141   if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src))
1142     return transformZExtICmp(ICI, CI);
1143 
1144   BinaryOperator *SrcI = dyn_cast<BinaryOperator>(Src);
1145   if (SrcI && SrcI->getOpcode() == Instruction::Or) {
1146     // zext (or icmp, icmp) -> or (zext icmp), (zext icmp) if at least one
1147     // of the (zext icmp) can be eliminated. If so, immediately perform the
1148     // according elimination.
1149     ICmpInst *LHS = dyn_cast<ICmpInst>(SrcI->getOperand(0));
1150     ICmpInst *RHS = dyn_cast<ICmpInst>(SrcI->getOperand(1));
1151     if (LHS && RHS && LHS->hasOneUse() && RHS->hasOneUse() &&
1152         (transformZExtICmp(LHS, CI, false) ||
1153          transformZExtICmp(RHS, CI, false))) {
1154       // zext (or icmp, icmp) -> or (zext icmp), (zext icmp)
1155       Value *LCast = Builder.CreateZExt(LHS, CI.getType(), LHS->getName());
1156       Value *RCast = Builder.CreateZExt(RHS, CI.getType(), RHS->getName());
1157       BinaryOperator *Or = BinaryOperator::Create(Instruction::Or, LCast, RCast);
1158 
1159       // Perform the elimination.
1160       if (auto *LZExt = dyn_cast<ZExtInst>(LCast))
1161         transformZExtICmp(LHS, *LZExt);
1162       if (auto *RZExt = dyn_cast<ZExtInst>(RCast))
1163         transformZExtICmp(RHS, *RZExt);
1164 
1165       return Or;
1166     }
1167   }
1168 
1169   // zext(trunc(X) & C) -> (X & zext(C)).
1170   Constant *C;
1171   Value *X;
1172   if (SrcI &&
1173       match(SrcI, m_OneUse(m_And(m_Trunc(m_Value(X)), m_Constant(C)))) &&
1174       X->getType() == CI.getType())
1175     return BinaryOperator::CreateAnd(X, ConstantExpr::getZExt(C, CI.getType()));
1176 
1177   // zext((trunc(X) & C) ^ C) -> ((X & zext(C)) ^ zext(C)).
1178   Value *And;
1179   if (SrcI && match(SrcI, m_OneUse(m_Xor(m_Value(And), m_Constant(C)))) &&
1180       match(And, m_OneUse(m_And(m_Trunc(m_Value(X)), m_Specific(C)))) &&
1181       X->getType() == CI.getType()) {
1182     Constant *ZC = ConstantExpr::getZExt(C, CI.getType());
1183     return BinaryOperator::CreateXor(Builder.CreateAnd(X, ZC), ZC);
1184   }
1185 
1186   return nullptr;
1187 }
1188 
1189 /// Transform (sext icmp) to bitwise / integer operations to eliminate the icmp.
transformSExtICmp(ICmpInst * ICI,Instruction & CI)1190 Instruction *InstCombiner::transformSExtICmp(ICmpInst *ICI, Instruction &CI) {
1191   Value *Op0 = ICI->getOperand(0), *Op1 = ICI->getOperand(1);
1192   ICmpInst::Predicate Pred = ICI->getPredicate();
1193 
1194   // Don't bother if Op1 isn't of vector or integer type.
1195   if (!Op1->getType()->isIntOrIntVectorTy())
1196     return nullptr;
1197 
1198   if ((Pred == ICmpInst::ICMP_SLT && match(Op1, m_ZeroInt())) ||
1199       (Pred == ICmpInst::ICMP_SGT && match(Op1, m_AllOnes()))) {
1200     // (x <s  0) ? -1 : 0 -> ashr x, 31        -> all ones if negative
1201     // (x >s -1) ? -1 : 0 -> not (ashr x, 31)  -> all ones if positive
1202     Value *Sh = ConstantInt::get(Op0->getType(),
1203                                  Op0->getType()->getScalarSizeInBits() - 1);
1204     Value *In = Builder.CreateAShr(Op0, Sh, Op0->getName() + ".lobit");
1205     if (In->getType() != CI.getType())
1206       In = Builder.CreateIntCast(In, CI.getType(), true /*SExt*/);
1207 
1208     if (Pred == ICmpInst::ICMP_SGT)
1209       In = Builder.CreateNot(In, In->getName() + ".not");
1210     return replaceInstUsesWith(CI, In);
1211   }
1212 
1213   if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
1214     // If we know that only one bit of the LHS of the icmp can be set and we
1215     // have an equality comparison with zero or a power of 2, we can transform
1216     // the icmp and sext into bitwise/integer operations.
1217     if (ICI->hasOneUse() &&
1218         ICI->isEquality() && (Op1C->isZero() || Op1C->getValue().isPowerOf2())){
1219       KnownBits Known = computeKnownBits(Op0, 0, &CI);
1220 
1221       APInt KnownZeroMask(~Known.Zero);
1222       if (KnownZeroMask.isPowerOf2()) {
1223         Value *In = ICI->getOperand(0);
1224 
1225         // If the icmp tests for a known zero bit we can constant fold it.
1226         if (!Op1C->isZero() && Op1C->getValue() != KnownZeroMask) {
1227           Value *V = Pred == ICmpInst::ICMP_NE ?
1228                        ConstantInt::getAllOnesValue(CI.getType()) :
1229                        ConstantInt::getNullValue(CI.getType());
1230           return replaceInstUsesWith(CI, V);
1231         }
1232 
1233         if (!Op1C->isZero() == (Pred == ICmpInst::ICMP_NE)) {
1234           // sext ((x & 2^n) == 0)   -> (x >> n) - 1
1235           // sext ((x & 2^n) != 2^n) -> (x >> n) - 1
1236           unsigned ShiftAmt = KnownZeroMask.countTrailingZeros();
1237           // Perform a right shift to place the desired bit in the LSB.
1238           if (ShiftAmt)
1239             In = Builder.CreateLShr(In,
1240                                     ConstantInt::get(In->getType(), ShiftAmt));
1241 
1242           // At this point "In" is either 1 or 0. Subtract 1 to turn
1243           // {1, 0} -> {0, -1}.
1244           In = Builder.CreateAdd(In,
1245                                  ConstantInt::getAllOnesValue(In->getType()),
1246                                  "sext");
1247         } else {
1248           // sext ((x & 2^n) != 0)   -> (x << bitwidth-n) a>> bitwidth-1
1249           // sext ((x & 2^n) == 2^n) -> (x << bitwidth-n) a>> bitwidth-1
1250           unsigned ShiftAmt = KnownZeroMask.countLeadingZeros();
1251           // Perform a left shift to place the desired bit in the MSB.
1252           if (ShiftAmt)
1253             In = Builder.CreateShl(In,
1254                                    ConstantInt::get(In->getType(), ShiftAmt));
1255 
1256           // Distribute the bit over the whole bit width.
1257           In = Builder.CreateAShr(In, ConstantInt::get(In->getType(),
1258                                   KnownZeroMask.getBitWidth() - 1), "sext");
1259         }
1260 
1261         if (CI.getType() == In->getType())
1262           return replaceInstUsesWith(CI, In);
1263         return CastInst::CreateIntegerCast(In, CI.getType(), true/*SExt*/);
1264       }
1265     }
1266   }
1267 
1268   return nullptr;
1269 }
1270 
1271 /// Return true if we can take the specified value and return it as type Ty
1272 /// without inserting any new casts and without changing the value of the common
1273 /// low bits.  This is used by code that tries to promote integer operations to
1274 /// a wider types will allow us to eliminate the extension.
1275 ///
1276 /// This function works on both vectors and scalars.
1277 ///
canEvaluateSExtd(Value * V,Type * Ty)1278 static bool canEvaluateSExtd(Value *V, Type *Ty) {
1279   assert(V->getType()->getScalarSizeInBits() < Ty->getScalarSizeInBits() &&
1280          "Can't sign extend type to a smaller type");
1281   if (canAlwaysEvaluateInType(V, Ty))
1282     return true;
1283   if (canNotEvaluateInType(V, Ty))
1284     return false;
1285 
1286   auto *I = cast<Instruction>(V);
1287   switch (I->getOpcode()) {
1288   case Instruction::SExt:  // sext(sext(x)) -> sext(x)
1289   case Instruction::ZExt:  // sext(zext(x)) -> zext(x)
1290   case Instruction::Trunc: // sext(trunc(x)) -> trunc(x) or sext(x)
1291     return true;
1292   case Instruction::And:
1293   case Instruction::Or:
1294   case Instruction::Xor:
1295   case Instruction::Add:
1296   case Instruction::Sub:
1297   case Instruction::Mul:
1298     // These operators can all arbitrarily be extended if their inputs can.
1299     return canEvaluateSExtd(I->getOperand(0), Ty) &&
1300            canEvaluateSExtd(I->getOperand(1), Ty);
1301 
1302   //case Instruction::Shl:   TODO
1303   //case Instruction::LShr:  TODO
1304 
1305   case Instruction::Select:
1306     return canEvaluateSExtd(I->getOperand(1), Ty) &&
1307            canEvaluateSExtd(I->getOperand(2), Ty);
1308 
1309   case Instruction::PHI: {
1310     // We can change a phi if we can change all operands.  Note that we never
1311     // get into trouble with cyclic PHIs here because we only consider
1312     // instructions with a single use.
1313     PHINode *PN = cast<PHINode>(I);
1314     for (Value *IncValue : PN->incoming_values())
1315       if (!canEvaluateSExtd(IncValue, Ty)) return false;
1316     return true;
1317   }
1318   default:
1319     // TODO: Can handle more cases here.
1320     break;
1321   }
1322 
1323   return false;
1324 }
1325 
visitSExt(SExtInst & CI)1326 Instruction *InstCombiner::visitSExt(SExtInst &CI) {
1327   // If this sign extend is only used by a truncate, let the truncate be
1328   // eliminated before we try to optimize this sext.
1329   if (CI.hasOneUse() && isa<TruncInst>(CI.user_back()))
1330     return nullptr;
1331 
1332   if (Instruction *I = commonCastTransforms(CI))
1333     return I;
1334 
1335   Value *Src = CI.getOperand(0);
1336   Type *SrcTy = Src->getType(), *DestTy = CI.getType();
1337 
1338   // If we know that the value being extended is positive, we can use a zext
1339   // instead.
1340   KnownBits Known = computeKnownBits(Src, 0, &CI);
1341   if (Known.isNonNegative()) {
1342     Value *ZExt = Builder.CreateZExt(Src, DestTy);
1343     return replaceInstUsesWith(CI, ZExt);
1344   }
1345 
1346   // Attempt to extend the entire input expression tree to the destination
1347   // type.   Only do this if the dest type is a simple type, don't convert the
1348   // expression tree to something weird like i93 unless the source is also
1349   // strange.
1350   if ((DestTy->isVectorTy() || shouldChangeType(SrcTy, DestTy)) &&
1351       canEvaluateSExtd(Src, DestTy)) {
1352     // Okay, we can transform this!  Insert the new expression now.
1353     LLVM_DEBUG(
1354         dbgs() << "ICE: EvaluateInDifferentType converting expression type"
1355                   " to avoid sign extend: "
1356                << CI << '\n');
1357     Value *Res = EvaluateInDifferentType(Src, DestTy, true);
1358     assert(Res->getType() == DestTy);
1359 
1360     uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
1361     uint32_t DestBitSize = DestTy->getScalarSizeInBits();
1362 
1363     // If the high bits are already filled with sign bit, just replace this
1364     // cast with the result.
1365     if (ComputeNumSignBits(Res, 0, &CI) > DestBitSize - SrcBitSize)
1366       return replaceInstUsesWith(CI, Res);
1367 
1368     // We need to emit a shl + ashr to do the sign extend.
1369     Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize);
1370     return BinaryOperator::CreateAShr(Builder.CreateShl(Res, ShAmt, "sext"),
1371                                       ShAmt);
1372   }
1373 
1374   // If the input is a trunc from the destination type, then turn sext(trunc(x))
1375   // into shifts.
1376   Value *X;
1377   if (match(Src, m_OneUse(m_Trunc(m_Value(X)))) && X->getType() == DestTy) {
1378     // sext(trunc(X)) --> ashr(shl(X, C), C)
1379     unsigned SrcBitSize = SrcTy->getScalarSizeInBits();
1380     unsigned DestBitSize = DestTy->getScalarSizeInBits();
1381     Constant *ShAmt = ConstantInt::get(DestTy, DestBitSize - SrcBitSize);
1382     return BinaryOperator::CreateAShr(Builder.CreateShl(X, ShAmt), ShAmt);
1383   }
1384 
1385   if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src))
1386     return transformSExtICmp(ICI, CI);
1387 
1388   // If the input is a shl/ashr pair of a same constant, then this is a sign
1389   // extension from a smaller value.  If we could trust arbitrary bitwidth
1390   // integers, we could turn this into a truncate to the smaller bit and then
1391   // use a sext for the whole extension.  Since we don't, look deeper and check
1392   // for a truncate.  If the source and dest are the same type, eliminate the
1393   // trunc and extend and just do shifts.  For example, turn:
1394   //   %a = trunc i32 %i to i8
1395   //   %b = shl i8 %a, 6
1396   //   %c = ashr i8 %b, 6
1397   //   %d = sext i8 %c to i32
1398   // into:
1399   //   %a = shl i32 %i, 30
1400   //   %d = ashr i32 %a, 30
1401   Value *A = nullptr;
1402   // TODO: Eventually this could be subsumed by EvaluateInDifferentType.
1403   ConstantInt *BA = nullptr, *CA = nullptr;
1404   if (match(Src, m_AShr(m_Shl(m_Trunc(m_Value(A)), m_ConstantInt(BA)),
1405                         m_ConstantInt(CA))) &&
1406       BA == CA && A->getType() == CI.getType()) {
1407     unsigned MidSize = Src->getType()->getScalarSizeInBits();
1408     unsigned SrcDstSize = CI.getType()->getScalarSizeInBits();
1409     unsigned ShAmt = CA->getZExtValue()+SrcDstSize-MidSize;
1410     Constant *ShAmtV = ConstantInt::get(CI.getType(), ShAmt);
1411     A = Builder.CreateShl(A, ShAmtV, CI.getName());
1412     return BinaryOperator::CreateAShr(A, ShAmtV);
1413   }
1414 
1415   return nullptr;
1416 }
1417 
1418 
1419 /// Return a Constant* for the specified floating-point constant if it fits
1420 /// in the specified FP type without changing its value.
fitsInFPType(ConstantFP * CFP,const fltSemantics & Sem)1421 static bool fitsInFPType(ConstantFP *CFP, const fltSemantics &Sem) {
1422   bool losesInfo;
1423   APFloat F = CFP->getValueAPF();
1424   (void)F.convert(Sem, APFloat::rmNearestTiesToEven, &losesInfo);
1425   return !losesInfo;
1426 }
1427 
shrinkFPConstant(ConstantFP * CFP)1428 static Type *shrinkFPConstant(ConstantFP *CFP) {
1429   if (CFP->getType() == Type::getPPC_FP128Ty(CFP->getContext()))
1430     return nullptr;  // No constant folding of this.
1431   // See if the value can be truncated to half and then reextended.
1432   if (fitsInFPType(CFP, APFloat::IEEEhalf()))
1433     return Type::getHalfTy(CFP->getContext());
1434   // See if the value can be truncated to float and then reextended.
1435   if (fitsInFPType(CFP, APFloat::IEEEsingle()))
1436     return Type::getFloatTy(CFP->getContext());
1437   if (CFP->getType()->isDoubleTy())
1438     return nullptr;  // Won't shrink.
1439   if (fitsInFPType(CFP, APFloat::IEEEdouble()))
1440     return Type::getDoubleTy(CFP->getContext());
1441   // Don't try to shrink to various long double types.
1442   return nullptr;
1443 }
1444 
1445 // Determine if this is a vector of ConstantFPs and if so, return the minimal
1446 // type we can safely truncate all elements to.
1447 // TODO: Make these support undef elements.
shrinkFPConstantVector(Value * V)1448 static Type *shrinkFPConstantVector(Value *V) {
1449   auto *CV = dyn_cast<Constant>(V);
1450   if (!CV || !CV->getType()->isVectorTy())
1451     return nullptr;
1452 
1453   Type *MinType = nullptr;
1454 
1455   unsigned NumElts = CV->getType()->getVectorNumElements();
1456   for (unsigned i = 0; i != NumElts; ++i) {
1457     auto *CFP = dyn_cast_or_null<ConstantFP>(CV->getAggregateElement(i));
1458     if (!CFP)
1459       return nullptr;
1460 
1461     Type *T = shrinkFPConstant(CFP);
1462     if (!T)
1463       return nullptr;
1464 
1465     // If we haven't found a type yet or this type has a larger mantissa than
1466     // our previous type, this is our new minimal type.
1467     if (!MinType || T->getFPMantissaWidth() > MinType->getFPMantissaWidth())
1468       MinType = T;
1469   }
1470 
1471   // Make a vector type from the minimal type.
1472   return VectorType::get(MinType, NumElts);
1473 }
1474 
1475 /// Find the minimum FP type we can safely truncate to.
getMinimumFPType(Value * V)1476 static Type *getMinimumFPType(Value *V) {
1477   if (auto *FPExt = dyn_cast<FPExtInst>(V))
1478     return FPExt->getOperand(0)->getType();
1479 
1480   // If this value is a constant, return the constant in the smallest FP type
1481   // that can accurately represent it.  This allows us to turn
1482   // (float)((double)X+2.0) into x+2.0f.
1483   if (auto *CFP = dyn_cast<ConstantFP>(V))
1484     if (Type *T = shrinkFPConstant(CFP))
1485       return T;
1486 
1487   // Try to shrink a vector of FP constants.
1488   if (Type *T = shrinkFPConstantVector(V))
1489     return T;
1490 
1491   return V->getType();
1492 }
1493 
visitFPTrunc(FPTruncInst & FPT)1494 Instruction *InstCombiner::visitFPTrunc(FPTruncInst &FPT) {
1495   if (Instruction *I = commonCastTransforms(FPT))
1496     return I;
1497 
1498   // If we have fptrunc(OpI (fpextend x), (fpextend y)), we would like to
1499   // simplify this expression to avoid one or more of the trunc/extend
1500   // operations if we can do so without changing the numerical results.
1501   //
1502   // The exact manner in which the widths of the operands interact to limit
1503   // what we can and cannot do safely varies from operation to operation, and
1504   // is explained below in the various case statements.
1505   Type *Ty = FPT.getType();
1506   BinaryOperator *OpI = dyn_cast<BinaryOperator>(FPT.getOperand(0));
1507   if (OpI && OpI->hasOneUse()) {
1508     Type *LHSMinType = getMinimumFPType(OpI->getOperand(0));
1509     Type *RHSMinType = getMinimumFPType(OpI->getOperand(1));
1510     unsigned OpWidth = OpI->getType()->getFPMantissaWidth();
1511     unsigned LHSWidth = LHSMinType->getFPMantissaWidth();
1512     unsigned RHSWidth = RHSMinType->getFPMantissaWidth();
1513     unsigned SrcWidth = std::max(LHSWidth, RHSWidth);
1514     unsigned DstWidth = Ty->getFPMantissaWidth();
1515     switch (OpI->getOpcode()) {
1516       default: break;
1517       case Instruction::FAdd:
1518       case Instruction::FSub:
1519         // For addition and subtraction, the infinitely precise result can
1520         // essentially be arbitrarily wide; proving that double rounding
1521         // will not occur because the result of OpI is exact (as we will for
1522         // FMul, for example) is hopeless.  However, we *can* nonetheless
1523         // frequently know that double rounding cannot occur (or that it is
1524         // innocuous) by taking advantage of the specific structure of
1525         // infinitely-precise results that admit double rounding.
1526         //
1527         // Specifically, if OpWidth >= 2*DstWdith+1 and DstWidth is sufficient
1528         // to represent both sources, we can guarantee that the double
1529         // rounding is innocuous (See p50 of Figueroa's 2000 PhD thesis,
1530         // "A Rigorous Framework for Fully Supporting the IEEE Standard ..."
1531         // for proof of this fact).
1532         //
1533         // Note: Figueroa does not consider the case where DstFormat !=
1534         // SrcFormat.  It's possible (likely even!) that this analysis
1535         // could be tightened for those cases, but they are rare (the main
1536         // case of interest here is (float)((double)float + float)).
1537         if (OpWidth >= 2*DstWidth+1 && DstWidth >= SrcWidth) {
1538           Value *LHS = Builder.CreateFPTrunc(OpI->getOperand(0), Ty);
1539           Value *RHS = Builder.CreateFPTrunc(OpI->getOperand(1), Ty);
1540           Instruction *RI = BinaryOperator::Create(OpI->getOpcode(), LHS, RHS);
1541           RI->copyFastMathFlags(OpI);
1542           return RI;
1543         }
1544         break;
1545       case Instruction::FMul:
1546         // For multiplication, the infinitely precise result has at most
1547         // LHSWidth + RHSWidth significant bits; if OpWidth is sufficient
1548         // that such a value can be exactly represented, then no double
1549         // rounding can possibly occur; we can safely perform the operation
1550         // in the destination format if it can represent both sources.
1551         if (OpWidth >= LHSWidth + RHSWidth && DstWidth >= SrcWidth) {
1552           Value *LHS = Builder.CreateFPTrunc(OpI->getOperand(0), Ty);
1553           Value *RHS = Builder.CreateFPTrunc(OpI->getOperand(1), Ty);
1554           return BinaryOperator::CreateFMulFMF(LHS, RHS, OpI);
1555         }
1556         break;
1557       case Instruction::FDiv:
1558         // For division, we use again use the bound from Figueroa's
1559         // dissertation.  I am entirely certain that this bound can be
1560         // tightened in the unbalanced operand case by an analysis based on
1561         // the diophantine rational approximation bound, but the well-known
1562         // condition used here is a good conservative first pass.
1563         // TODO: Tighten bound via rigorous analysis of the unbalanced case.
1564         if (OpWidth >= 2*DstWidth && DstWidth >= SrcWidth) {
1565           Value *LHS = Builder.CreateFPTrunc(OpI->getOperand(0), Ty);
1566           Value *RHS = Builder.CreateFPTrunc(OpI->getOperand(1), Ty);
1567           return BinaryOperator::CreateFDivFMF(LHS, RHS, OpI);
1568         }
1569         break;
1570       case Instruction::FRem: {
1571         // Remainder is straightforward.  Remainder is always exact, so the
1572         // type of OpI doesn't enter into things at all.  We simply evaluate
1573         // in whichever source type is larger, then convert to the
1574         // destination type.
1575         if (SrcWidth == OpWidth)
1576           break;
1577         Value *LHS, *RHS;
1578         if (LHSWidth == SrcWidth) {
1579            LHS = Builder.CreateFPTrunc(OpI->getOperand(0), LHSMinType);
1580            RHS = Builder.CreateFPTrunc(OpI->getOperand(1), LHSMinType);
1581         } else {
1582            LHS = Builder.CreateFPTrunc(OpI->getOperand(0), RHSMinType);
1583            RHS = Builder.CreateFPTrunc(OpI->getOperand(1), RHSMinType);
1584         }
1585 
1586         Value *ExactResult = Builder.CreateFRemFMF(LHS, RHS, OpI);
1587         return CastInst::CreateFPCast(ExactResult, Ty);
1588       }
1589     }
1590 
1591     // (fptrunc (fneg x)) -> (fneg (fptrunc x))
1592     if (BinaryOperator::isFNeg(OpI)) {
1593       Value *InnerTrunc = Builder.CreateFPTrunc(OpI->getOperand(1), Ty);
1594       return BinaryOperator::CreateFNegFMF(InnerTrunc, OpI);
1595     }
1596   }
1597 
1598   if (auto *II = dyn_cast<IntrinsicInst>(FPT.getOperand(0))) {
1599     switch (II->getIntrinsicID()) {
1600     default: break;
1601     case Intrinsic::ceil:
1602     case Intrinsic::fabs:
1603     case Intrinsic::floor:
1604     case Intrinsic::nearbyint:
1605     case Intrinsic::rint:
1606     case Intrinsic::round:
1607     case Intrinsic::trunc: {
1608       Value *Src = II->getArgOperand(0);
1609       if (!Src->hasOneUse())
1610         break;
1611 
1612       // Except for fabs, this transformation requires the input of the unary FP
1613       // operation to be itself an fpext from the type to which we're
1614       // truncating.
1615       if (II->getIntrinsicID() != Intrinsic::fabs) {
1616         FPExtInst *FPExtSrc = dyn_cast<FPExtInst>(Src);
1617         if (!FPExtSrc || FPExtSrc->getSrcTy() != Ty)
1618           break;
1619       }
1620 
1621       // Do unary FP operation on smaller type.
1622       // (fptrunc (fabs x)) -> (fabs (fptrunc x))
1623       Value *InnerTrunc = Builder.CreateFPTrunc(Src, Ty);
1624       Function *Overload = Intrinsic::getDeclaration(FPT.getModule(),
1625                                                      II->getIntrinsicID(), Ty);
1626       SmallVector<OperandBundleDef, 1> OpBundles;
1627       II->getOperandBundlesAsDefs(OpBundles);
1628       CallInst *NewCI = CallInst::Create(Overload, { InnerTrunc }, OpBundles,
1629                                          II->getName());
1630       NewCI->copyFastMathFlags(II);
1631       return NewCI;
1632     }
1633     }
1634   }
1635 
1636   if (Instruction *I = shrinkInsertElt(FPT, Builder))
1637     return I;
1638 
1639   return nullptr;
1640 }
1641 
visitFPExt(CastInst & CI)1642 Instruction *InstCombiner::visitFPExt(CastInst &CI) {
1643   return commonCastTransforms(CI);
1644 }
1645 
1646 // fpto{s/u}i({u/s}itofp(X)) --> X or zext(X) or sext(X) or trunc(X)
1647 // This is safe if the intermediate type has enough bits in its mantissa to
1648 // accurately represent all values of X.  For example, this won't work with
1649 // i64 -> float -> i64.
FoldItoFPtoI(Instruction & FI)1650 Instruction *InstCombiner::FoldItoFPtoI(Instruction &FI) {
1651   if (!isa<UIToFPInst>(FI.getOperand(0)) && !isa<SIToFPInst>(FI.getOperand(0)))
1652     return nullptr;
1653   Instruction *OpI = cast<Instruction>(FI.getOperand(0));
1654 
1655   Value *SrcI = OpI->getOperand(0);
1656   Type *FITy = FI.getType();
1657   Type *OpITy = OpI->getType();
1658   Type *SrcTy = SrcI->getType();
1659   bool IsInputSigned = isa<SIToFPInst>(OpI);
1660   bool IsOutputSigned = isa<FPToSIInst>(FI);
1661 
1662   // We can safely assume the conversion won't overflow the output range,
1663   // because (for example) (uint8_t)18293.f is undefined behavior.
1664 
1665   // Since we can assume the conversion won't overflow, our decision as to
1666   // whether the input will fit in the float should depend on the minimum
1667   // of the input range and output range.
1668 
1669   // This means this is also safe for a signed input and unsigned output, since
1670   // a negative input would lead to undefined behavior.
1671   int InputSize = (int)SrcTy->getScalarSizeInBits() - IsInputSigned;
1672   int OutputSize = (int)FITy->getScalarSizeInBits() - IsOutputSigned;
1673   int ActualSize = std::min(InputSize, OutputSize);
1674 
1675   if (ActualSize <= OpITy->getFPMantissaWidth()) {
1676     if (FITy->getScalarSizeInBits() > SrcTy->getScalarSizeInBits()) {
1677       if (IsInputSigned && IsOutputSigned)
1678         return new SExtInst(SrcI, FITy);
1679       return new ZExtInst(SrcI, FITy);
1680     }
1681     if (FITy->getScalarSizeInBits() < SrcTy->getScalarSizeInBits())
1682       return new TruncInst(SrcI, FITy);
1683     if (SrcTy == FITy)
1684       return replaceInstUsesWith(FI, SrcI);
1685     return new BitCastInst(SrcI, FITy);
1686   }
1687   return nullptr;
1688 }
1689 
visitFPToUI(FPToUIInst & FI)1690 Instruction *InstCombiner::visitFPToUI(FPToUIInst &FI) {
1691   Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0));
1692   if (!OpI)
1693     return commonCastTransforms(FI);
1694 
1695   if (Instruction *I = FoldItoFPtoI(FI))
1696     return I;
1697 
1698   return commonCastTransforms(FI);
1699 }
1700 
visitFPToSI(FPToSIInst & FI)1701 Instruction *InstCombiner::visitFPToSI(FPToSIInst &FI) {
1702   Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0));
1703   if (!OpI)
1704     return commonCastTransforms(FI);
1705 
1706   if (Instruction *I = FoldItoFPtoI(FI))
1707     return I;
1708 
1709   return commonCastTransforms(FI);
1710 }
1711 
visitUIToFP(CastInst & CI)1712 Instruction *InstCombiner::visitUIToFP(CastInst &CI) {
1713   return commonCastTransforms(CI);
1714 }
1715 
visitSIToFP(CastInst & CI)1716 Instruction *InstCombiner::visitSIToFP(CastInst &CI) {
1717   return commonCastTransforms(CI);
1718 }
1719 
visitIntToPtr(IntToPtrInst & CI)1720 Instruction *InstCombiner::visitIntToPtr(IntToPtrInst &CI) {
1721   // If the source integer type is not the intptr_t type for this target, do a
1722   // trunc or zext to the intptr_t type, then inttoptr of it.  This allows the
1723   // cast to be exposed to other transforms.
1724   unsigned AS = CI.getAddressSpace();
1725   if (CI.getOperand(0)->getType()->getScalarSizeInBits() !=
1726       DL.getPointerSizeInBits(AS)) {
1727     Type *Ty = DL.getIntPtrType(CI.getContext(), AS);
1728     if (CI.getType()->isVectorTy()) // Handle vectors of pointers.
1729       Ty = VectorType::get(Ty, CI.getType()->getVectorNumElements());
1730 
1731     Value *P = Builder.CreateZExtOrTrunc(CI.getOperand(0), Ty);
1732     return new IntToPtrInst(P, CI.getType());
1733   }
1734 
1735   if (Instruction *I = commonCastTransforms(CI))
1736     return I;
1737 
1738   return nullptr;
1739 }
1740 
1741 /// Implement the transforms for cast of pointer (bitcast/ptrtoint)
commonPointerCastTransforms(CastInst & CI)1742 Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) {
1743   Value *Src = CI.getOperand(0);
1744 
1745   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Src)) {
1746     // If casting the result of a getelementptr instruction with no offset, turn
1747     // this into a cast of the original pointer!
1748     if (GEP->hasAllZeroIndices() &&
1749         // If CI is an addrspacecast and GEP changes the poiner type, merging
1750         // GEP into CI would undo canonicalizing addrspacecast with different
1751         // pointer types, causing infinite loops.
1752         (!isa<AddrSpaceCastInst>(CI) ||
1753          GEP->getType() == GEP->getPointerOperandType())) {
1754       // Changing the cast operand is usually not a good idea but it is safe
1755       // here because the pointer operand is being replaced with another
1756       // pointer operand so the opcode doesn't need to change.
1757       Worklist.Add(GEP);
1758       CI.setOperand(0, GEP->getOperand(0));
1759       return &CI;
1760     }
1761   }
1762 
1763   return commonCastTransforms(CI);
1764 }
1765 
visitPtrToInt(PtrToIntInst & CI)1766 Instruction *InstCombiner::visitPtrToInt(PtrToIntInst &CI) {
1767   // If the destination integer type is not the intptr_t type for this target,
1768   // do a ptrtoint to intptr_t then do a trunc or zext.  This allows the cast
1769   // to be exposed to other transforms.
1770 
1771   Type *Ty = CI.getType();
1772   unsigned AS = CI.getPointerAddressSpace();
1773 
1774   if (Ty->getScalarSizeInBits() == DL.getIndexSizeInBits(AS))
1775     return commonPointerCastTransforms(CI);
1776 
1777   Type *PtrTy = DL.getIntPtrType(CI.getContext(), AS);
1778   if (Ty->isVectorTy()) // Handle vectors of pointers.
1779     PtrTy = VectorType::get(PtrTy, Ty->getVectorNumElements());
1780 
1781   Value *P = Builder.CreatePtrToInt(CI.getOperand(0), PtrTy);
1782   return CastInst::CreateIntegerCast(P, Ty, /*isSigned=*/false);
1783 }
1784 
1785 /// This input value (which is known to have vector type) is being zero extended
1786 /// or truncated to the specified vector type.
1787 /// Try to replace it with a shuffle (and vector/vector bitcast) if possible.
1788 ///
1789 /// The source and destination vector types may have different element types.
optimizeVectorResize(Value * InVal,VectorType * DestTy,InstCombiner & IC)1790 static Instruction *optimizeVectorResize(Value *InVal, VectorType *DestTy,
1791                                          InstCombiner &IC) {
1792   // We can only do this optimization if the output is a multiple of the input
1793   // element size, or the input is a multiple of the output element size.
1794   // Convert the input type to have the same element type as the output.
1795   VectorType *SrcTy = cast<VectorType>(InVal->getType());
1796 
1797   if (SrcTy->getElementType() != DestTy->getElementType()) {
1798     // The input types don't need to be identical, but for now they must be the
1799     // same size.  There is no specific reason we couldn't handle things like
1800     // <4 x i16> -> <4 x i32> by bitcasting to <2 x i32> but haven't gotten
1801     // there yet.
1802     if (SrcTy->getElementType()->getPrimitiveSizeInBits() !=
1803         DestTy->getElementType()->getPrimitiveSizeInBits())
1804       return nullptr;
1805 
1806     SrcTy = VectorType::get(DestTy->getElementType(), SrcTy->getNumElements());
1807     InVal = IC.Builder.CreateBitCast(InVal, SrcTy);
1808   }
1809 
1810   // Now that the element types match, get the shuffle mask and RHS of the
1811   // shuffle to use, which depends on whether we're increasing or decreasing the
1812   // size of the input.
1813   SmallVector<uint32_t, 16> ShuffleMask;
1814   Value *V2;
1815 
1816   if (SrcTy->getNumElements() > DestTy->getNumElements()) {
1817     // If we're shrinking the number of elements, just shuffle in the low
1818     // elements from the input and use undef as the second shuffle input.
1819     V2 = UndefValue::get(SrcTy);
1820     for (unsigned i = 0, e = DestTy->getNumElements(); i != e; ++i)
1821       ShuffleMask.push_back(i);
1822 
1823   } else {
1824     // If we're increasing the number of elements, shuffle in all of the
1825     // elements from InVal and fill the rest of the result elements with zeros
1826     // from a constant zero.
1827     V2 = Constant::getNullValue(SrcTy);
1828     unsigned SrcElts = SrcTy->getNumElements();
1829     for (unsigned i = 0, e = SrcElts; i != e; ++i)
1830       ShuffleMask.push_back(i);
1831 
1832     // The excess elements reference the first element of the zero input.
1833     for (unsigned i = 0, e = DestTy->getNumElements()-SrcElts; i != e; ++i)
1834       ShuffleMask.push_back(SrcElts);
1835   }
1836 
1837   return new ShuffleVectorInst(InVal, V2,
1838                                ConstantDataVector::get(V2->getContext(),
1839                                                        ShuffleMask));
1840 }
1841 
isMultipleOfTypeSize(unsigned Value,Type * Ty)1842 static bool isMultipleOfTypeSize(unsigned Value, Type *Ty) {
1843   return Value % Ty->getPrimitiveSizeInBits() == 0;
1844 }
1845 
getTypeSizeIndex(unsigned Value,Type * Ty)1846 static unsigned getTypeSizeIndex(unsigned Value, Type *Ty) {
1847   return Value / Ty->getPrimitiveSizeInBits();
1848 }
1849 
1850 /// V is a value which is inserted into a vector of VecEltTy.
1851 /// Look through the value to see if we can decompose it into
1852 /// insertions into the vector.  See the example in the comment for
1853 /// OptimizeIntegerToVectorInsertions for the pattern this handles.
1854 /// The type of V is always a non-zero multiple of VecEltTy's size.
1855 /// Shift is the number of bits between the lsb of V and the lsb of
1856 /// the vector.
1857 ///
1858 /// This returns false if the pattern can't be matched or true if it can,
1859 /// filling in Elements with the elements found here.
collectInsertionElements(Value * V,unsigned Shift,SmallVectorImpl<Value * > & Elements,Type * VecEltTy,bool isBigEndian)1860 static bool collectInsertionElements(Value *V, unsigned Shift,
1861                                      SmallVectorImpl<Value *> &Elements,
1862                                      Type *VecEltTy, bool isBigEndian) {
1863   assert(isMultipleOfTypeSize(Shift, VecEltTy) &&
1864          "Shift should be a multiple of the element type size");
1865 
1866   // Undef values never contribute useful bits to the result.
1867   if (isa<UndefValue>(V)) return true;
1868 
1869   // If we got down to a value of the right type, we win, try inserting into the
1870   // right element.
1871   if (V->getType() == VecEltTy) {
1872     // Inserting null doesn't actually insert any elements.
1873     if (Constant *C = dyn_cast<Constant>(V))
1874       if (C->isNullValue())
1875         return true;
1876 
1877     unsigned ElementIndex = getTypeSizeIndex(Shift, VecEltTy);
1878     if (isBigEndian)
1879       ElementIndex = Elements.size() - ElementIndex - 1;
1880 
1881     // Fail if multiple elements are inserted into this slot.
1882     if (Elements[ElementIndex])
1883       return false;
1884 
1885     Elements[ElementIndex] = V;
1886     return true;
1887   }
1888 
1889   if (Constant *C = dyn_cast<Constant>(V)) {
1890     // Figure out the # elements this provides, and bitcast it or slice it up
1891     // as required.
1892     unsigned NumElts = getTypeSizeIndex(C->getType()->getPrimitiveSizeInBits(),
1893                                         VecEltTy);
1894     // If the constant is the size of a vector element, we just need to bitcast
1895     // it to the right type so it gets properly inserted.
1896     if (NumElts == 1)
1897       return collectInsertionElements(ConstantExpr::getBitCast(C, VecEltTy),
1898                                       Shift, Elements, VecEltTy, isBigEndian);
1899 
1900     // Okay, this is a constant that covers multiple elements.  Slice it up into
1901     // pieces and insert each element-sized piece into the vector.
1902     if (!isa<IntegerType>(C->getType()))
1903       C = ConstantExpr::getBitCast(C, IntegerType::get(V->getContext(),
1904                                        C->getType()->getPrimitiveSizeInBits()));
1905     unsigned ElementSize = VecEltTy->getPrimitiveSizeInBits();
1906     Type *ElementIntTy = IntegerType::get(C->getContext(), ElementSize);
1907 
1908     for (unsigned i = 0; i != NumElts; ++i) {
1909       unsigned ShiftI = Shift+i*ElementSize;
1910       Constant *Piece = ConstantExpr::getLShr(C, ConstantInt::get(C->getType(),
1911                                                                   ShiftI));
1912       Piece = ConstantExpr::getTrunc(Piece, ElementIntTy);
1913       if (!collectInsertionElements(Piece, ShiftI, Elements, VecEltTy,
1914                                     isBigEndian))
1915         return false;
1916     }
1917     return true;
1918   }
1919 
1920   if (!V->hasOneUse()) return false;
1921 
1922   Instruction *I = dyn_cast<Instruction>(V);
1923   if (!I) return false;
1924   switch (I->getOpcode()) {
1925   default: return false; // Unhandled case.
1926   case Instruction::BitCast:
1927     return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
1928                                     isBigEndian);
1929   case Instruction::ZExt:
1930     if (!isMultipleOfTypeSize(
1931                           I->getOperand(0)->getType()->getPrimitiveSizeInBits(),
1932                               VecEltTy))
1933       return false;
1934     return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
1935                                     isBigEndian);
1936   case Instruction::Or:
1937     return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
1938                                     isBigEndian) &&
1939            collectInsertionElements(I->getOperand(1), Shift, Elements, VecEltTy,
1940                                     isBigEndian);
1941   case Instruction::Shl: {
1942     // Must be shifting by a constant that is a multiple of the element size.
1943     ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1));
1944     if (!CI) return false;
1945     Shift += CI->getZExtValue();
1946     if (!isMultipleOfTypeSize(Shift, VecEltTy)) return false;
1947     return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
1948                                     isBigEndian);
1949   }
1950 
1951   }
1952 }
1953 
1954 
1955 /// If the input is an 'or' instruction, we may be doing shifts and ors to
1956 /// assemble the elements of the vector manually.
1957 /// Try to rip the code out and replace it with insertelements.  This is to
1958 /// optimize code like this:
1959 ///
1960 ///    %tmp37 = bitcast float %inc to i32
1961 ///    %tmp38 = zext i32 %tmp37 to i64
1962 ///    %tmp31 = bitcast float %inc5 to i32
1963 ///    %tmp32 = zext i32 %tmp31 to i64
1964 ///    %tmp33 = shl i64 %tmp32, 32
1965 ///    %ins35 = or i64 %tmp33, %tmp38
1966 ///    %tmp43 = bitcast i64 %ins35 to <2 x float>
1967 ///
1968 /// Into two insertelements that do "buildvector{%inc, %inc5}".
optimizeIntegerToVectorInsertions(BitCastInst & CI,InstCombiner & IC)1969 static Value *optimizeIntegerToVectorInsertions(BitCastInst &CI,
1970                                                 InstCombiner &IC) {
1971   VectorType *DestVecTy = cast<VectorType>(CI.getType());
1972   Value *IntInput = CI.getOperand(0);
1973 
1974   SmallVector<Value*, 8> Elements(DestVecTy->getNumElements());
1975   if (!collectInsertionElements(IntInput, 0, Elements,
1976                                 DestVecTy->getElementType(),
1977                                 IC.getDataLayout().isBigEndian()))
1978     return nullptr;
1979 
1980   // If we succeeded, we know that all of the element are specified by Elements
1981   // or are zero if Elements has a null entry.  Recast this as a set of
1982   // insertions.
1983   Value *Result = Constant::getNullValue(CI.getType());
1984   for (unsigned i = 0, e = Elements.size(); i != e; ++i) {
1985     if (!Elements[i]) continue;  // Unset element.
1986 
1987     Result = IC.Builder.CreateInsertElement(Result, Elements[i],
1988                                             IC.Builder.getInt32(i));
1989   }
1990 
1991   return Result;
1992 }
1993 
1994 /// Canonicalize scalar bitcasts of extracted elements into a bitcast of the
1995 /// vector followed by extract element. The backend tends to handle bitcasts of
1996 /// vectors better than bitcasts of scalars because vector registers are
1997 /// usually not type-specific like scalar integer or scalar floating-point.
canonicalizeBitCastExtElt(BitCastInst & BitCast,InstCombiner & IC)1998 static Instruction *canonicalizeBitCastExtElt(BitCastInst &BitCast,
1999                                               InstCombiner &IC) {
2000   // TODO: Create and use a pattern matcher for ExtractElementInst.
2001   auto *ExtElt = dyn_cast<ExtractElementInst>(BitCast.getOperand(0));
2002   if (!ExtElt || !ExtElt->hasOneUse())
2003     return nullptr;
2004 
2005   // The bitcast must be to a vectorizable type, otherwise we can't make a new
2006   // type to extract from.
2007   Type *DestType = BitCast.getType();
2008   if (!VectorType::isValidElementType(DestType))
2009     return nullptr;
2010 
2011   unsigned NumElts = ExtElt->getVectorOperandType()->getNumElements();
2012   auto *NewVecType = VectorType::get(DestType, NumElts);
2013   auto *NewBC = IC.Builder.CreateBitCast(ExtElt->getVectorOperand(),
2014                                          NewVecType, "bc");
2015   return ExtractElementInst::Create(NewBC, ExtElt->getIndexOperand());
2016 }
2017 
2018 /// Change the type of a bitwise logic operation if we can eliminate a bitcast.
foldBitCastBitwiseLogic(BitCastInst & BitCast,InstCombiner::BuilderTy & Builder)2019 static Instruction *foldBitCastBitwiseLogic(BitCastInst &BitCast,
2020                                             InstCombiner::BuilderTy &Builder) {
2021   Type *DestTy = BitCast.getType();
2022   BinaryOperator *BO;
2023   if (!DestTy->isIntOrIntVectorTy() ||
2024       !match(BitCast.getOperand(0), m_OneUse(m_BinOp(BO))) ||
2025       !BO->isBitwiseLogicOp())
2026     return nullptr;
2027 
2028   // FIXME: This transform is restricted to vector types to avoid backend
2029   // problems caused by creating potentially illegal operations. If a fix-up is
2030   // added to handle that situation, we can remove this check.
2031   if (!DestTy->isVectorTy() || !BO->getType()->isVectorTy())
2032     return nullptr;
2033 
2034   Value *X;
2035   if (match(BO->getOperand(0), m_OneUse(m_BitCast(m_Value(X)))) &&
2036       X->getType() == DestTy && !isa<Constant>(X)) {
2037     // bitcast(logic(bitcast(X), Y)) --> logic'(X, bitcast(Y))
2038     Value *CastedOp1 = Builder.CreateBitCast(BO->getOperand(1), DestTy);
2039     return BinaryOperator::Create(BO->getOpcode(), X, CastedOp1);
2040   }
2041 
2042   if (match(BO->getOperand(1), m_OneUse(m_BitCast(m_Value(X)))) &&
2043       X->getType() == DestTy && !isa<Constant>(X)) {
2044     // bitcast(logic(Y, bitcast(X))) --> logic'(bitcast(Y), X)
2045     Value *CastedOp0 = Builder.CreateBitCast(BO->getOperand(0), DestTy);
2046     return BinaryOperator::Create(BO->getOpcode(), CastedOp0, X);
2047   }
2048 
2049   // Canonicalize vector bitcasts to come before vector bitwise logic with a
2050   // constant. This eases recognition of special constants for later ops.
2051   // Example:
2052   // icmp u/s (a ^ signmask), (b ^ signmask) --> icmp s/u a, b
2053   Constant *C;
2054   if (match(BO->getOperand(1), m_Constant(C))) {
2055     // bitcast (logic X, C) --> logic (bitcast X, C')
2056     Value *CastedOp0 = Builder.CreateBitCast(BO->getOperand(0), DestTy);
2057     Value *CastedC = ConstantExpr::getBitCast(C, DestTy);
2058     return BinaryOperator::Create(BO->getOpcode(), CastedOp0, CastedC);
2059   }
2060 
2061   return nullptr;
2062 }
2063 
2064 /// Change the type of a select if we can eliminate a bitcast.
foldBitCastSelect(BitCastInst & BitCast,InstCombiner::BuilderTy & Builder)2065 static Instruction *foldBitCastSelect(BitCastInst &BitCast,
2066                                       InstCombiner::BuilderTy &Builder) {
2067   Value *Cond, *TVal, *FVal;
2068   if (!match(BitCast.getOperand(0),
2069              m_OneUse(m_Select(m_Value(Cond), m_Value(TVal), m_Value(FVal)))))
2070     return nullptr;
2071 
2072   // A vector select must maintain the same number of elements in its operands.
2073   Type *CondTy = Cond->getType();
2074   Type *DestTy = BitCast.getType();
2075   if (CondTy->isVectorTy()) {
2076     if (!DestTy->isVectorTy())
2077       return nullptr;
2078     if (DestTy->getVectorNumElements() != CondTy->getVectorNumElements())
2079       return nullptr;
2080   }
2081 
2082   // FIXME: This transform is restricted from changing the select between
2083   // scalars and vectors to avoid backend problems caused by creating
2084   // potentially illegal operations. If a fix-up is added to handle that
2085   // situation, we can remove this check.
2086   if (DestTy->isVectorTy() != TVal->getType()->isVectorTy())
2087     return nullptr;
2088 
2089   auto *Sel = cast<Instruction>(BitCast.getOperand(0));
2090   Value *X;
2091   if (match(TVal, m_OneUse(m_BitCast(m_Value(X)))) && X->getType() == DestTy &&
2092       !isa<Constant>(X)) {
2093     // bitcast(select(Cond, bitcast(X), Y)) --> select'(Cond, X, bitcast(Y))
2094     Value *CastedVal = Builder.CreateBitCast(FVal, DestTy);
2095     return SelectInst::Create(Cond, X, CastedVal, "", nullptr, Sel);
2096   }
2097 
2098   if (match(FVal, m_OneUse(m_BitCast(m_Value(X)))) && X->getType() == DestTy &&
2099       !isa<Constant>(X)) {
2100     // bitcast(select(Cond, Y, bitcast(X))) --> select'(Cond, bitcast(Y), X)
2101     Value *CastedVal = Builder.CreateBitCast(TVal, DestTy);
2102     return SelectInst::Create(Cond, CastedVal, X, "", nullptr, Sel);
2103   }
2104 
2105   return nullptr;
2106 }
2107 
2108 /// Check if all users of CI are StoreInsts.
hasStoreUsersOnly(CastInst & CI)2109 static bool hasStoreUsersOnly(CastInst &CI) {
2110   for (User *U : CI.users()) {
2111     if (!isa<StoreInst>(U))
2112       return false;
2113   }
2114   return true;
2115 }
2116 
2117 /// This function handles following case
2118 ///
2119 ///     A  ->  B    cast
2120 ///     PHI
2121 ///     B  ->  A    cast
2122 ///
2123 /// All the related PHI nodes can be replaced by new PHI nodes with type A.
2124 /// The uses of \p CI can be changed to the new PHI node corresponding to \p PN.
optimizeBitCastFromPhi(CastInst & CI,PHINode * PN)2125 Instruction *InstCombiner::optimizeBitCastFromPhi(CastInst &CI, PHINode *PN) {
2126   // BitCast used by Store can be handled in InstCombineLoadStoreAlloca.cpp.
2127   if (hasStoreUsersOnly(CI))
2128     return nullptr;
2129 
2130   Value *Src = CI.getOperand(0);
2131   Type *SrcTy = Src->getType();         // Type B
2132   Type *DestTy = CI.getType();          // Type A
2133 
2134   SmallVector<PHINode *, 4> PhiWorklist;
2135   SmallSetVector<PHINode *, 4> OldPhiNodes;
2136 
2137   // Find all of the A->B casts and PHI nodes.
2138   // We need to inpect all related PHI nodes, but PHIs can be cyclic, so
2139   // OldPhiNodes is used to track all known PHI nodes, before adding a new
2140   // PHI to PhiWorklist, it is checked against and added to OldPhiNodes first.
2141   PhiWorklist.push_back(PN);
2142   OldPhiNodes.insert(PN);
2143   while (!PhiWorklist.empty()) {
2144     auto *OldPN = PhiWorklist.pop_back_val();
2145     for (Value *IncValue : OldPN->incoming_values()) {
2146       if (isa<Constant>(IncValue))
2147         continue;
2148 
2149       if (auto *LI = dyn_cast<LoadInst>(IncValue)) {
2150         // If there is a sequence of one or more load instructions, each loaded
2151         // value is used as address of later load instruction, bitcast is
2152         // necessary to change the value type, don't optimize it. For
2153         // simplicity we give up if the load address comes from another load.
2154         Value *Addr = LI->getOperand(0);
2155         if (Addr == &CI || isa<LoadInst>(Addr))
2156           return nullptr;
2157         if (LI->hasOneUse() && LI->isSimple())
2158           continue;
2159         // If a LoadInst has more than one use, changing the type of loaded
2160         // value may create another bitcast.
2161         return nullptr;
2162       }
2163 
2164       if (auto *PNode = dyn_cast<PHINode>(IncValue)) {
2165         if (OldPhiNodes.insert(PNode))
2166           PhiWorklist.push_back(PNode);
2167         continue;
2168       }
2169 
2170       auto *BCI = dyn_cast<BitCastInst>(IncValue);
2171       // We can't handle other instructions.
2172       if (!BCI)
2173         return nullptr;
2174 
2175       // Verify it's a A->B cast.
2176       Type *TyA = BCI->getOperand(0)->getType();
2177       Type *TyB = BCI->getType();
2178       if (TyA != DestTy || TyB != SrcTy)
2179         return nullptr;
2180     }
2181   }
2182 
2183   // For each old PHI node, create a corresponding new PHI node with a type A.
2184   SmallDenseMap<PHINode *, PHINode *> NewPNodes;
2185   for (auto *OldPN : OldPhiNodes) {
2186     Builder.SetInsertPoint(OldPN);
2187     PHINode *NewPN = Builder.CreatePHI(DestTy, OldPN->getNumOperands());
2188     NewPNodes[OldPN] = NewPN;
2189   }
2190 
2191   // Fill in the operands of new PHI nodes.
2192   for (auto *OldPN : OldPhiNodes) {
2193     PHINode *NewPN = NewPNodes[OldPN];
2194     for (unsigned j = 0, e = OldPN->getNumOperands(); j != e; ++j) {
2195       Value *V = OldPN->getOperand(j);
2196       Value *NewV = nullptr;
2197       if (auto *C = dyn_cast<Constant>(V)) {
2198         NewV = ConstantExpr::getBitCast(C, DestTy);
2199       } else if (auto *LI = dyn_cast<LoadInst>(V)) {
2200         Builder.SetInsertPoint(LI->getNextNode());
2201         NewV = Builder.CreateBitCast(LI, DestTy);
2202         Worklist.Add(LI);
2203       } else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
2204         NewV = BCI->getOperand(0);
2205       } else if (auto *PrevPN = dyn_cast<PHINode>(V)) {
2206         NewV = NewPNodes[PrevPN];
2207       }
2208       assert(NewV);
2209       NewPN->addIncoming(NewV, OldPN->getIncomingBlock(j));
2210     }
2211   }
2212 
2213   // If there is a store with type B, change it to type A.
2214   for (User *U : PN->users()) {
2215     auto *SI = dyn_cast<StoreInst>(U);
2216     if (SI && SI->isSimple() && SI->getOperand(0) == PN) {
2217       Builder.SetInsertPoint(SI);
2218       auto *NewBC =
2219           cast<BitCastInst>(Builder.CreateBitCast(NewPNodes[PN], SrcTy));
2220       SI->setOperand(0, NewBC);
2221       Worklist.Add(SI);
2222       assert(hasStoreUsersOnly(*NewBC));
2223     }
2224   }
2225 
2226   return replaceInstUsesWith(CI, NewPNodes[PN]);
2227 }
2228 
visitBitCast(BitCastInst & CI)2229 Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
2230   // If the operands are integer typed then apply the integer transforms,
2231   // otherwise just apply the common ones.
2232   Value *Src = CI.getOperand(0);
2233   Type *SrcTy = Src->getType();
2234   Type *DestTy = CI.getType();
2235 
2236   // Get rid of casts from one type to the same type. These are useless and can
2237   // be replaced by the operand.
2238   if (DestTy == Src->getType())
2239     return replaceInstUsesWith(CI, Src);
2240 
2241   if (PointerType *DstPTy = dyn_cast<PointerType>(DestTy)) {
2242     PointerType *SrcPTy = cast<PointerType>(SrcTy);
2243     Type *DstElTy = DstPTy->getElementType();
2244     Type *SrcElTy = SrcPTy->getElementType();
2245 
2246     // Casting pointers between the same type, but with different address spaces
2247     // is an addrspace cast rather than a bitcast.
2248     if ((DstElTy == SrcElTy) &&
2249         (DstPTy->getAddressSpace() != SrcPTy->getAddressSpace()))
2250       return new AddrSpaceCastInst(Src, DestTy);
2251 
2252     // If we are casting a alloca to a pointer to a type of the same
2253     // size, rewrite the allocation instruction to allocate the "right" type.
2254     // There is no need to modify malloc calls because it is their bitcast that
2255     // needs to be cleaned up.
2256     if (AllocaInst *AI = dyn_cast<AllocaInst>(Src))
2257       if (Instruction *V = PromoteCastOfAllocation(CI, *AI))
2258         return V;
2259 
2260     // When the type pointed to is not sized the cast cannot be
2261     // turned into a gep.
2262     Type *PointeeType =
2263         cast<PointerType>(Src->getType()->getScalarType())->getElementType();
2264     if (!PointeeType->isSized())
2265       return nullptr;
2266 
2267     // If the source and destination are pointers, and this cast is equivalent
2268     // to a getelementptr X, 0, 0, 0...  turn it into the appropriate gep.
2269     // This can enhance SROA and other transforms that want type-safe pointers.
2270     unsigned NumZeros = 0;
2271     while (SrcElTy != DstElTy &&
2272            isa<CompositeType>(SrcElTy) && !SrcElTy->isPointerTy() &&
2273            SrcElTy->getNumContainedTypes() /* not "{}" */) {
2274       SrcElTy = cast<CompositeType>(SrcElTy)->getTypeAtIndex(0U);
2275       ++NumZeros;
2276     }
2277 
2278     // If we found a path from the src to dest, create the getelementptr now.
2279     if (SrcElTy == DstElTy) {
2280       SmallVector<Value *, 8> Idxs(NumZeros + 1, Builder.getInt32(0));
2281       return GetElementPtrInst::CreateInBounds(Src, Idxs);
2282     }
2283   }
2284 
2285   if (VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) {
2286     if (DestVTy->getNumElements() == 1 && !SrcTy->isVectorTy()) {
2287       Value *Elem = Builder.CreateBitCast(Src, DestVTy->getElementType());
2288       return InsertElementInst::Create(UndefValue::get(DestTy), Elem,
2289                      Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
2290       // FIXME: Canonicalize bitcast(insertelement) -> insertelement(bitcast)
2291     }
2292 
2293     if (isa<IntegerType>(SrcTy)) {
2294       // If this is a cast from an integer to vector, check to see if the input
2295       // is a trunc or zext of a bitcast from vector.  If so, we can replace all
2296       // the casts with a shuffle and (potentially) a bitcast.
2297       if (isa<TruncInst>(Src) || isa<ZExtInst>(Src)) {
2298         CastInst *SrcCast = cast<CastInst>(Src);
2299         if (BitCastInst *BCIn = dyn_cast<BitCastInst>(SrcCast->getOperand(0)))
2300           if (isa<VectorType>(BCIn->getOperand(0)->getType()))
2301             if (Instruction *I = optimizeVectorResize(BCIn->getOperand(0),
2302                                                cast<VectorType>(DestTy), *this))
2303               return I;
2304       }
2305 
2306       // If the input is an 'or' instruction, we may be doing shifts and ors to
2307       // assemble the elements of the vector manually.  Try to rip the code out
2308       // and replace it with insertelements.
2309       if (Value *V = optimizeIntegerToVectorInsertions(CI, *this))
2310         return replaceInstUsesWith(CI, V);
2311     }
2312   }
2313 
2314   if (VectorType *SrcVTy = dyn_cast<VectorType>(SrcTy)) {
2315     if (SrcVTy->getNumElements() == 1) {
2316       // If our destination is not a vector, then make this a straight
2317       // scalar-scalar cast.
2318       if (!DestTy->isVectorTy()) {
2319         Value *Elem =
2320           Builder.CreateExtractElement(Src,
2321                      Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
2322         return CastInst::Create(Instruction::BitCast, Elem, DestTy);
2323       }
2324 
2325       // Otherwise, see if our source is an insert. If so, then use the scalar
2326       // component directly.
2327       if (InsertElementInst *IEI =
2328             dyn_cast<InsertElementInst>(CI.getOperand(0)))
2329         return CastInst::Create(Instruction::BitCast, IEI->getOperand(1),
2330                                 DestTy);
2331     }
2332   }
2333 
2334   if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(Src)) {
2335     // Okay, we have (bitcast (shuffle ..)).  Check to see if this is
2336     // a bitcast to a vector with the same # elts.
2337     if (SVI->hasOneUse() && DestTy->isVectorTy() &&
2338         DestTy->getVectorNumElements() == SVI->getType()->getNumElements() &&
2339         SVI->getType()->getNumElements() ==
2340         SVI->getOperand(0)->getType()->getVectorNumElements()) {
2341       BitCastInst *Tmp;
2342       // If either of the operands is a cast from CI.getType(), then
2343       // evaluating the shuffle in the casted destination's type will allow
2344       // us to eliminate at least one cast.
2345       if (((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(0))) &&
2346            Tmp->getOperand(0)->getType() == DestTy) ||
2347           ((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(1))) &&
2348            Tmp->getOperand(0)->getType() == DestTy)) {
2349         Value *LHS = Builder.CreateBitCast(SVI->getOperand(0), DestTy);
2350         Value *RHS = Builder.CreateBitCast(SVI->getOperand(1), DestTy);
2351         // Return a new shuffle vector.  Use the same element ID's, as we
2352         // know the vector types match #elts.
2353         return new ShuffleVectorInst(LHS, RHS, SVI->getOperand(2));
2354       }
2355     }
2356   }
2357 
2358   // Handle the A->B->A cast, and there is an intervening PHI node.
2359   if (PHINode *PN = dyn_cast<PHINode>(Src))
2360     if (Instruction *I = optimizeBitCastFromPhi(CI, PN))
2361       return I;
2362 
2363   if (Instruction *I = canonicalizeBitCastExtElt(CI, *this))
2364     return I;
2365 
2366   if (Instruction *I = foldBitCastBitwiseLogic(CI, Builder))
2367     return I;
2368 
2369   if (Instruction *I = foldBitCastSelect(CI, Builder))
2370     return I;
2371 
2372   if (SrcTy->isPointerTy())
2373     return commonPointerCastTransforms(CI);
2374   return commonCastTransforms(CI);
2375 }
2376 
visitAddrSpaceCast(AddrSpaceCastInst & CI)2377 Instruction *InstCombiner::visitAddrSpaceCast(AddrSpaceCastInst &CI) {
2378   // If the destination pointer element type is not the same as the source's
2379   // first do a bitcast to the destination type, and then the addrspacecast.
2380   // This allows the cast to be exposed to other transforms.
2381   Value *Src = CI.getOperand(0);
2382   PointerType *SrcTy = cast<PointerType>(Src->getType()->getScalarType());
2383   PointerType *DestTy = cast<PointerType>(CI.getType()->getScalarType());
2384 
2385   Type *DestElemTy = DestTy->getElementType();
2386   if (SrcTy->getElementType() != DestElemTy) {
2387     Type *MidTy = PointerType::get(DestElemTy, SrcTy->getAddressSpace());
2388     if (VectorType *VT = dyn_cast<VectorType>(CI.getType())) {
2389       // Handle vectors of pointers.
2390       MidTy = VectorType::get(MidTy, VT->getNumElements());
2391     }
2392 
2393     Value *NewBitCast = Builder.CreateBitCast(Src, MidTy);
2394     return new AddrSpaceCastInst(NewBitCast, CI.getType());
2395   }
2396 
2397   return commonPointerCastTransforms(CI);
2398 }
2399