1 //===- InstCombineSelect.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 visitSelect function.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "InstCombine.h"
15 #include "llvm/Analysis/ConstantFolding.h"
16 #include "llvm/Analysis/InstructionSimplify.h"
17 #include "llvm/IR/PatternMatch.h"
18 using namespace llvm;
19 using namespace PatternMatch;
20
21 #define DEBUG_TYPE "instcombine"
22
23 /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
24 /// returning the kind and providing the out parameter results if we
25 /// successfully match.
26 static SelectPatternFlavor
MatchSelectPattern(Value * V,Value * & LHS,Value * & RHS)27 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
28 SelectInst *SI = dyn_cast<SelectInst>(V);
29 if (!SI) return SPF_UNKNOWN;
30
31 ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
32 if (!ICI) return SPF_UNKNOWN;
33
34 ICmpInst::Predicate Pred = ICI->getPredicate();
35 Value *CmpLHS = ICI->getOperand(0);
36 Value *CmpRHS = ICI->getOperand(1);
37 Value *TrueVal = SI->getTrueValue();
38 Value *FalseVal = SI->getFalseValue();
39
40 LHS = CmpLHS;
41 RHS = CmpRHS;
42
43 // (icmp X, Y) ? X : Y
44 if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
45 switch (Pred) {
46 default: return SPF_UNKNOWN; // Equality.
47 case ICmpInst::ICMP_UGT:
48 case ICmpInst::ICMP_UGE: return SPF_UMAX;
49 case ICmpInst::ICMP_SGT:
50 case ICmpInst::ICMP_SGE: return SPF_SMAX;
51 case ICmpInst::ICMP_ULT:
52 case ICmpInst::ICMP_ULE: return SPF_UMIN;
53 case ICmpInst::ICMP_SLT:
54 case ICmpInst::ICMP_SLE: return SPF_SMIN;
55 }
56 }
57
58 // (icmp X, Y) ? Y : X
59 if (TrueVal == CmpRHS && FalseVal == CmpLHS) {
60 switch (Pred) {
61 default: return SPF_UNKNOWN; // Equality.
62 case ICmpInst::ICMP_UGT:
63 case ICmpInst::ICMP_UGE: return SPF_UMIN;
64 case ICmpInst::ICMP_SGT:
65 case ICmpInst::ICMP_SGE: return SPF_SMIN;
66 case ICmpInst::ICMP_ULT:
67 case ICmpInst::ICMP_ULE: return SPF_UMAX;
68 case ICmpInst::ICMP_SLT:
69 case ICmpInst::ICMP_SLE: return SPF_SMAX;
70 }
71 }
72
73 if (ConstantInt *C1 = dyn_cast<ConstantInt>(CmpRHS)) {
74 if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
75 (CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {
76
77 // ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
78 // NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
79 if (Pred == ICmpInst::ICMP_SGT && (C1->isZero() || C1->isMinusOne())) {
80 return (CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS;
81 }
82
83 // ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
84 // NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
85 if (Pred == ICmpInst::ICMP_SLT && (C1->isZero() || C1->isOne())) {
86 return (CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS;
87 }
88 }
89 }
90
91 // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5)
92
93 return SPF_UNKNOWN;
94 }
95
96
97 /// GetSelectFoldableOperands - We want to turn code that looks like this:
98 /// %C = or %A, %B
99 /// %D = select %cond, %C, %A
100 /// into:
101 /// %C = select %cond, %B, 0
102 /// %D = or %A, %C
103 ///
104 /// Assuming that the specified instruction is an operand to the select, return
105 /// a bitmask indicating which operands of this instruction are foldable if they
106 /// equal the other incoming value of the select.
107 ///
GetSelectFoldableOperands(Instruction * I)108 static unsigned GetSelectFoldableOperands(Instruction *I) {
109 switch (I->getOpcode()) {
110 case Instruction::Add:
111 case Instruction::Mul:
112 case Instruction::And:
113 case Instruction::Or:
114 case Instruction::Xor:
115 return 3; // Can fold through either operand.
116 case Instruction::Sub: // Can only fold on the amount subtracted.
117 case Instruction::Shl: // Can only fold on the shift amount.
118 case Instruction::LShr:
119 case Instruction::AShr:
120 return 1;
121 default:
122 return 0; // Cannot fold
123 }
124 }
125
126 /// GetSelectFoldableConstant - For the same transformation as the previous
127 /// function, return the identity constant that goes into the select.
GetSelectFoldableConstant(Instruction * I)128 static Constant *GetSelectFoldableConstant(Instruction *I) {
129 switch (I->getOpcode()) {
130 default: llvm_unreachable("This cannot happen!");
131 case Instruction::Add:
132 case Instruction::Sub:
133 case Instruction::Or:
134 case Instruction::Xor:
135 case Instruction::Shl:
136 case Instruction::LShr:
137 case Instruction::AShr:
138 return Constant::getNullValue(I->getType());
139 case Instruction::And:
140 return Constant::getAllOnesValue(I->getType());
141 case Instruction::Mul:
142 return ConstantInt::get(I->getType(), 1);
143 }
144 }
145
146 /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI
147 /// have the same opcode and only one use each. Try to simplify this.
FoldSelectOpOp(SelectInst & SI,Instruction * TI,Instruction * FI)148 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
149 Instruction *FI) {
150 if (TI->getNumOperands() == 1) {
151 // If this is a non-volatile load or a cast from the same type,
152 // merge.
153 if (TI->isCast()) {
154 Type *FIOpndTy = FI->getOperand(0)->getType();
155 if (TI->getOperand(0)->getType() != FIOpndTy)
156 return nullptr;
157 // The select condition may be a vector. We may only change the operand
158 // type if the vector width remains the same (and matches the condition).
159 Type *CondTy = SI.getCondition()->getType();
160 if (CondTy->isVectorTy() && (!FIOpndTy->isVectorTy() ||
161 CondTy->getVectorNumElements() != FIOpndTy->getVectorNumElements()))
162 return nullptr;
163 } else {
164 return nullptr; // unknown unary op.
165 }
166
167 // Fold this by inserting a select from the input values.
168 Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0),
169 FI->getOperand(0), SI.getName()+".v");
170 return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
171 TI->getType());
172 }
173
174 // Only handle binary operators here.
175 if (!isa<BinaryOperator>(TI))
176 return nullptr;
177
178 // Figure out if the operations have any operands in common.
179 Value *MatchOp, *OtherOpT, *OtherOpF;
180 bool MatchIsOpZero;
181 if (TI->getOperand(0) == FI->getOperand(0)) {
182 MatchOp = TI->getOperand(0);
183 OtherOpT = TI->getOperand(1);
184 OtherOpF = FI->getOperand(1);
185 MatchIsOpZero = true;
186 } else if (TI->getOperand(1) == FI->getOperand(1)) {
187 MatchOp = TI->getOperand(1);
188 OtherOpT = TI->getOperand(0);
189 OtherOpF = FI->getOperand(0);
190 MatchIsOpZero = false;
191 } else if (!TI->isCommutative()) {
192 return nullptr;
193 } else if (TI->getOperand(0) == FI->getOperand(1)) {
194 MatchOp = TI->getOperand(0);
195 OtherOpT = TI->getOperand(1);
196 OtherOpF = FI->getOperand(0);
197 MatchIsOpZero = true;
198 } else if (TI->getOperand(1) == FI->getOperand(0)) {
199 MatchOp = TI->getOperand(1);
200 OtherOpT = TI->getOperand(0);
201 OtherOpF = FI->getOperand(1);
202 MatchIsOpZero = true;
203 } else {
204 return nullptr;
205 }
206
207 // If we reach here, they do have operations in common.
208 Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT,
209 OtherOpF, SI.getName()+".v");
210
211 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
212 if (MatchIsOpZero)
213 return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
214 else
215 return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
216 }
217 llvm_unreachable("Shouldn't get here");
218 }
219
isSelect01(Constant * C1,Constant * C2)220 static bool isSelect01(Constant *C1, Constant *C2) {
221 ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
222 if (!C1I)
223 return false;
224 ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
225 if (!C2I)
226 return false;
227 if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
228 return false;
229 return C1I->isOne() || C1I->isAllOnesValue() ||
230 C2I->isOne() || C2I->isAllOnesValue();
231 }
232
233 /// FoldSelectIntoOp - Try fold the select into one of the operands to
234 /// facilitate further optimization.
FoldSelectIntoOp(SelectInst & SI,Value * TrueVal,Value * FalseVal)235 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
236 Value *FalseVal) {
237 // See the comment above GetSelectFoldableOperands for a description of the
238 // transformation we are doing here.
239 if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
240 if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
241 !isa<Constant>(FalseVal)) {
242 if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
243 unsigned OpToFold = 0;
244 if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
245 OpToFold = 1;
246 } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
247 OpToFold = 2;
248 }
249
250 if (OpToFold) {
251 Constant *C = GetSelectFoldableConstant(TVI);
252 Value *OOp = TVI->getOperand(2-OpToFold);
253 // Avoid creating select between 2 constants unless it's selecting
254 // between 0, 1 and -1.
255 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
256 Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C);
257 NewSel->takeName(TVI);
258 BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI);
259 BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(),
260 FalseVal, NewSel);
261 if (isa<PossiblyExactOperator>(BO))
262 BO->setIsExact(TVI_BO->isExact());
263 if (isa<OverflowingBinaryOperator>(BO)) {
264 BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap());
265 BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap());
266 }
267 return BO;
268 }
269 }
270 }
271 }
272 }
273
274 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
275 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
276 !isa<Constant>(TrueVal)) {
277 if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
278 unsigned OpToFold = 0;
279 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
280 OpToFold = 1;
281 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
282 OpToFold = 2;
283 }
284
285 if (OpToFold) {
286 Constant *C = GetSelectFoldableConstant(FVI);
287 Value *OOp = FVI->getOperand(2-OpToFold);
288 // Avoid creating select between 2 constants unless it's selecting
289 // between 0, 1 and -1.
290 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
291 Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp);
292 NewSel->takeName(FVI);
293 BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI);
294 BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(),
295 TrueVal, NewSel);
296 if (isa<PossiblyExactOperator>(BO))
297 BO->setIsExact(FVI_BO->isExact());
298 if (isa<OverflowingBinaryOperator>(BO)) {
299 BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap());
300 BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap());
301 }
302 return BO;
303 }
304 }
305 }
306 }
307 }
308
309 return nullptr;
310 }
311
312 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
313 /// replaced with RepOp.
SimplifyWithOpReplaced(Value * V,Value * Op,Value * RepOp,const DataLayout * TD,const TargetLibraryInfo * TLI)314 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
315 const DataLayout *TD,
316 const TargetLibraryInfo *TLI) {
317 // Trivial replacement.
318 if (V == Op)
319 return RepOp;
320
321 Instruction *I = dyn_cast<Instruction>(V);
322 if (!I)
323 return nullptr;
324
325 // If this is a binary operator, try to simplify it with the replaced op.
326 if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
327 if (B->getOperand(0) == Op)
328 return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD, TLI);
329 if (B->getOperand(1) == Op)
330 return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD, TLI);
331 }
332
333 // Same for CmpInsts.
334 if (CmpInst *C = dyn_cast<CmpInst>(I)) {
335 if (C->getOperand(0) == Op)
336 return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD,
337 TLI);
338 if (C->getOperand(1) == Op)
339 return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD,
340 TLI);
341 }
342
343 // TODO: We could hand off more cases to instsimplify here.
344
345 // If all operands are constant after substituting Op for RepOp then we can
346 // constant fold the instruction.
347 if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
348 // Build a list of all constant operands.
349 SmallVector<Constant*, 8> ConstOps;
350 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
351 if (I->getOperand(i) == Op)
352 ConstOps.push_back(CRepOp);
353 else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
354 ConstOps.push_back(COp);
355 else
356 break;
357 }
358
359 // All operands were constants, fold it.
360 if (ConstOps.size() == I->getNumOperands()) {
361 if (CmpInst *C = dyn_cast<CmpInst>(I))
362 return ConstantFoldCompareInstOperands(C->getPredicate(), ConstOps[0],
363 ConstOps[1], TD, TLI);
364
365 if (LoadInst *LI = dyn_cast<LoadInst>(I))
366 if (!LI->isVolatile())
367 return ConstantFoldLoadFromConstPtr(ConstOps[0], TD);
368
369 return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
370 ConstOps, TD, TLI);
371 }
372 }
373
374 return nullptr;
375 }
376
377 /// foldSelectICmpAndOr - We want to turn:
378 /// (select (icmp eq (and X, C1), 0), Y, (or Y, C2))
379 /// into:
380 /// (or (shl (and X, C1), C3), y)
381 /// iff:
382 /// C1 and C2 are both powers of 2
383 /// where:
384 /// C3 = Log(C2) - Log(C1)
385 ///
386 /// This transform handles cases where:
387 /// 1. The icmp predicate is inverted
388 /// 2. The select operands are reversed
389 /// 3. The magnitude of C2 and C1 are flipped
390 ///
391 /// This also tries to turn
392 /// --- Single bit tests:
393 /// if ((x & C) == 0) x |= C to x |= C
394 /// if ((x & C) != 0) x ^= C to x &= ~C
395 /// if ((x & C) == 0) x ^= C to x |= C
396 /// if ((x & C) != 0) x &= ~C to x &= ~C
397 /// if ((x & C) == 0) x &= ~C to nothing
foldSelectICmpAndOr(SelectInst & SI,Value * TrueVal,Value * FalseVal,InstCombiner::BuilderTy * Builder)398 static Value *foldSelectICmpAndOr(SelectInst &SI, Value *TrueVal,
399 Value *FalseVal,
400 InstCombiner::BuilderTy *Builder) {
401 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
402 if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
403 return nullptr;
404
405 Value *CmpLHS = IC->getOperand(0);
406 Value *CmpRHS = IC->getOperand(1);
407
408 if (!match(CmpRHS, m_Zero()))
409 return nullptr;
410
411 Value *X;
412 const APInt *C1;
413 if (!match(CmpLHS, m_And(m_Value(X), m_Power2(C1))))
414 return nullptr;
415
416 const APInt *C2;
417 if (match(TrueVal, m_Specific(X))) {
418 // if ((X & C) != 0) X ^= C becomes X &= ~C
419 if (match(FalseVal, m_Xor(m_Specific(X), m_APInt(C2))) && C1 == C2)
420 return Builder->CreateAnd(X, ~(*C1));
421 // if ((X & C) != 0) X &= ~C becomes X &= ~C
422 if (match(FalseVal, m_And(m_Specific(X), m_APInt(C2))) && *C1 == ~(*C2))
423 return FalseVal;
424 } else if (match(FalseVal, m_Specific(X))) {
425 // if ((X & C) == 0) X ^= C becomes X |= C
426 if (match(TrueVal, m_Xor(m_Specific(X), m_APInt(C2))) && C1 == C2)
427 return Builder->CreateOr(X, *C1);
428 // if ((X & C) == 0) X &= ~C becomes nothing
429 if (match(TrueVal, m_And(m_Specific(X), m_APInt(C2))) && *C1 == ~(*C2))
430 return X;
431 // if ((X & C) == 0) X |= C becomes X |= C
432 if (match(TrueVal, m_Or(m_Specific(X), m_APInt(C2))) && C1 == C2)
433 return TrueVal;
434 }
435
436 bool OrOnTrueVal = false;
437 bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
438 if (!OrOnFalseVal)
439 OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2)));
440
441 if (!OrOnFalseVal && !OrOnTrueVal)
442 return nullptr;
443
444 Value *V = CmpLHS;
445 Value *Y = OrOnFalseVal ? TrueVal : FalseVal;
446
447 unsigned C1Log = C1->logBase2();
448 unsigned C2Log = C2->logBase2();
449 if (C2Log > C1Log) {
450 V = Builder->CreateZExtOrTrunc(V, Y->getType());
451 V = Builder->CreateShl(V, C2Log - C1Log);
452 } else if (C1Log > C2Log) {
453 V = Builder->CreateLShr(V, C1Log - C2Log);
454 V = Builder->CreateZExtOrTrunc(V, Y->getType());
455 } else
456 V = Builder->CreateZExtOrTrunc(V, Y->getType());
457
458 ICmpInst::Predicate Pred = IC->getPredicate();
459 if ((Pred == ICmpInst::ICMP_NE && OrOnFalseVal) ||
460 (Pred == ICmpInst::ICMP_EQ && OrOnTrueVal))
461 V = Builder->CreateXor(V, *C2);
462
463 return Builder->CreateOr(V, Y);
464 }
465
466 /// visitSelectInstWithICmp - Visit a SelectInst that has an
467 /// ICmpInst as its first operand.
468 ///
visitSelectInstWithICmp(SelectInst & SI,ICmpInst * ICI)469 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
470 ICmpInst *ICI) {
471 bool Changed = false;
472 ICmpInst::Predicate Pred = ICI->getPredicate();
473 Value *CmpLHS = ICI->getOperand(0);
474 Value *CmpRHS = ICI->getOperand(1);
475 Value *TrueVal = SI.getTrueValue();
476 Value *FalseVal = SI.getFalseValue();
477
478 // Check cases where the comparison is with a constant that
479 // can be adjusted to fit the min/max idiom. We may move or edit ICI
480 // here, so make sure the select is the only user.
481 if (ICI->hasOneUse())
482 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
483 // X < MIN ? T : F --> F
484 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
485 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
486 return ReplaceInstUsesWith(SI, FalseVal);
487 // X > MAX ? T : F --> F
488 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
489 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
490 return ReplaceInstUsesWith(SI, FalseVal);
491 switch (Pred) {
492 default: break;
493 case ICmpInst::ICMP_ULT:
494 case ICmpInst::ICMP_SLT:
495 case ICmpInst::ICMP_UGT:
496 case ICmpInst::ICMP_SGT: {
497 // These transformations only work for selects over integers.
498 IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
499 if (!SelectTy)
500 break;
501
502 Constant *AdjustedRHS;
503 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
504 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
505 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
506 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
507
508 // X > C ? X : C+1 --> X < C+1 ? C+1 : X
509 // X < C ? X : C-1 --> X > C-1 ? C-1 : X
510 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
511 (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
512 ; // Nothing to do here. Values match without any sign/zero extension.
513
514 // Types do not match. Instead of calculating this with mixed types
515 // promote all to the larger type. This enables scalar evolution to
516 // analyze this expression.
517 else if (CmpRHS->getType()->getScalarSizeInBits()
518 < SelectTy->getBitWidth()) {
519 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
520
521 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
522 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
523 // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
524 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
525 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
526 sextRHS == FalseVal) {
527 CmpLHS = TrueVal;
528 AdjustedRHS = sextRHS;
529 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
530 sextRHS == TrueVal) {
531 CmpLHS = FalseVal;
532 AdjustedRHS = sextRHS;
533 } else if (ICI->isUnsigned()) {
534 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
535 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
536 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
537 // zext + signed compare cannot be changed:
538 // 0xff <s 0x00, but 0x00ff >s 0x0000
539 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
540 zextRHS == FalseVal) {
541 CmpLHS = TrueVal;
542 AdjustedRHS = zextRHS;
543 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
544 zextRHS == TrueVal) {
545 CmpLHS = FalseVal;
546 AdjustedRHS = zextRHS;
547 } else
548 break;
549 } else
550 break;
551 } else
552 break;
553
554 Pred = ICmpInst::getSwappedPredicate(Pred);
555 CmpRHS = AdjustedRHS;
556 std::swap(FalseVal, TrueVal);
557 ICI->setPredicate(Pred);
558 ICI->setOperand(0, CmpLHS);
559 ICI->setOperand(1, CmpRHS);
560 SI.setOperand(1, TrueVal);
561 SI.setOperand(2, FalseVal);
562
563 // Move ICI instruction right before the select instruction. Otherwise
564 // the sext/zext value may be defined after the ICI instruction uses it.
565 ICI->moveBefore(&SI);
566
567 Changed = true;
568 break;
569 }
570 }
571 }
572
573 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
574 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
575 // FIXME: Type and constness constraints could be lifted, but we have to
576 // watch code size carefully. We should consider xor instead of
577 // sub/add when we decide to do that.
578 if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
579 if (TrueVal->getType() == Ty) {
580 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
581 ConstantInt *C1 = nullptr, *C2 = nullptr;
582 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
583 C1 = dyn_cast<ConstantInt>(TrueVal);
584 C2 = dyn_cast<ConstantInt>(FalseVal);
585 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
586 C1 = dyn_cast<ConstantInt>(FalseVal);
587 C2 = dyn_cast<ConstantInt>(TrueVal);
588 }
589 if (C1 && C2) {
590 // This shift results in either -1 or 0.
591 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
592
593 // Check if we can express the operation with a single or.
594 if (C2->isAllOnesValue())
595 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
596
597 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
598 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
599 }
600 }
601 }
602 }
603
604 // If we have an equality comparison then we know the value in one of the
605 // arms of the select. See if substituting this value into the arm and
606 // simplifying the result yields the same value as the other arm.
607 if (Pred == ICmpInst::ICMP_EQ) {
608 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, DL, TLI) == TrueVal ||
609 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, DL, TLI) == TrueVal)
610 return ReplaceInstUsesWith(SI, FalseVal);
611 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, DL, TLI) == FalseVal ||
612 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, DL, TLI) == FalseVal)
613 return ReplaceInstUsesWith(SI, FalseVal);
614 } else if (Pred == ICmpInst::ICMP_NE) {
615 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, DL, TLI) == FalseVal ||
616 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, DL, TLI) == FalseVal)
617 return ReplaceInstUsesWith(SI, TrueVal);
618 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, DL, TLI) == TrueVal ||
619 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, DL, TLI) == TrueVal)
620 return ReplaceInstUsesWith(SI, TrueVal);
621 }
622
623 // NOTE: if we wanted to, this is where to detect integer MIN/MAX
624
625 if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
626 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
627 // Transform (X == C) ? X : Y -> (X == C) ? C : Y
628 SI.setOperand(1, CmpRHS);
629 Changed = true;
630 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
631 // Transform (X != C) ? Y : X -> (X != C) ? Y : C
632 SI.setOperand(2, CmpRHS);
633 Changed = true;
634 }
635 }
636
637 if (Value *V = foldSelectICmpAndOr(SI, TrueVal, FalseVal, Builder))
638 return ReplaceInstUsesWith(SI, V);
639
640 return Changed ? &SI : nullptr;
641 }
642
643
644 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
645 /// PHI node (but the two may be in different blocks). See if the true/false
646 /// values (V) are live in all of the predecessor blocks of the PHI. For
647 /// example, cases like this cannot be mapped:
648 ///
649 /// X = phi [ C1, BB1], [C2, BB2]
650 /// Y = add
651 /// Z = select X, Y, 0
652 ///
653 /// because Y is not live in BB1/BB2.
654 ///
CanSelectOperandBeMappingIntoPredBlock(const Value * V,const SelectInst & SI)655 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
656 const SelectInst &SI) {
657 // If the value is a non-instruction value like a constant or argument, it
658 // can always be mapped.
659 const Instruction *I = dyn_cast<Instruction>(V);
660 if (!I) return true;
661
662 // If V is a PHI node defined in the same block as the condition PHI, we can
663 // map the arguments.
664 const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
665
666 if (const PHINode *VP = dyn_cast<PHINode>(I))
667 if (VP->getParent() == CondPHI->getParent())
668 return true;
669
670 // Otherwise, if the PHI and select are defined in the same block and if V is
671 // defined in a different block, then we can transform it.
672 if (SI.getParent() == CondPHI->getParent() &&
673 I->getParent() != CondPHI->getParent())
674 return true;
675
676 // Otherwise we have a 'hard' case and we can't tell without doing more
677 // detailed dominator based analysis, punt.
678 return false;
679 }
680
681 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
682 /// SPF2(SPF1(A, B), C)
FoldSPFofSPF(Instruction * Inner,SelectPatternFlavor SPF1,Value * A,Value * B,Instruction & Outer,SelectPatternFlavor SPF2,Value * C)683 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
684 SelectPatternFlavor SPF1,
685 Value *A, Value *B,
686 Instruction &Outer,
687 SelectPatternFlavor SPF2, Value *C) {
688 if (C == A || C == B) {
689 // MAX(MAX(A, B), B) -> MAX(A, B)
690 // MIN(MIN(a, b), a) -> MIN(a, b)
691 if (SPF1 == SPF2)
692 return ReplaceInstUsesWith(Outer, Inner);
693
694 // MAX(MIN(a, b), a) -> a
695 // MIN(MAX(a, b), a) -> a
696 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
697 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
698 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
699 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
700 return ReplaceInstUsesWith(Outer, C);
701 }
702
703 if (SPF1 == SPF2) {
704 if (ConstantInt *CB = dyn_cast<ConstantInt>(B)) {
705 if (ConstantInt *CC = dyn_cast<ConstantInt>(C)) {
706 APInt ACB = CB->getValue();
707 APInt ACC = CC->getValue();
708
709 // MIN(MIN(A, 23), 97) -> MIN(A, 23)
710 // MAX(MAX(A, 97), 23) -> MAX(A, 97)
711 if ((SPF1 == SPF_UMIN && ACB.ule(ACC)) ||
712 (SPF1 == SPF_SMIN && ACB.sle(ACC)) ||
713 (SPF1 == SPF_UMAX && ACB.uge(ACC)) ||
714 (SPF1 == SPF_SMAX && ACB.sge(ACC)))
715 return ReplaceInstUsesWith(Outer, Inner);
716
717 // MIN(MIN(A, 97), 23) -> MIN(A, 23)
718 // MAX(MAX(A, 23), 97) -> MAX(A, 97)
719 if ((SPF1 == SPF_UMIN && ACB.ugt(ACC)) ||
720 (SPF1 == SPF_SMIN && ACB.sgt(ACC)) ||
721 (SPF1 == SPF_UMAX && ACB.ult(ACC)) ||
722 (SPF1 == SPF_SMAX && ACB.slt(ACC))) {
723 Outer.replaceUsesOfWith(Inner, A);
724 return &Outer;
725 }
726 }
727 }
728 }
729
730 // ABS(ABS(X)) -> ABS(X)
731 // NABS(NABS(X)) -> NABS(X)
732 if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
733 return ReplaceInstUsesWith(Outer, Inner);
734 }
735
736 // ABS(NABS(X)) -> ABS(X)
737 // NABS(ABS(X)) -> NABS(X)
738 if ((SPF1 == SPF_ABS && SPF2 == SPF_NABS) ||
739 (SPF1 == SPF_NABS && SPF2 == SPF_ABS)) {
740 SelectInst *SI = cast<SelectInst>(Inner);
741 Value *NewSI = Builder->CreateSelect(
742 SI->getCondition(), SI->getFalseValue(), SI->getTrueValue());
743 return ReplaceInstUsesWith(Outer, NewSI);
744 }
745 return nullptr;
746 }
747
748 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
749 /// both be) and we have an icmp instruction with zero, and we have an 'and'
750 /// with the non-constant value and a power of two we can turn the select
751 /// into a shift on the result of the 'and'.
foldSelectICmpAnd(const SelectInst & SI,ConstantInt * TrueVal,ConstantInt * FalseVal,InstCombiner::BuilderTy * Builder)752 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
753 ConstantInt *FalseVal,
754 InstCombiner::BuilderTy *Builder) {
755 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
756 if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
757 return nullptr;
758
759 if (!match(IC->getOperand(1), m_Zero()))
760 return nullptr;
761
762 ConstantInt *AndRHS;
763 Value *LHS = IC->getOperand(0);
764 if (!match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
765 return nullptr;
766
767 // If both select arms are non-zero see if we have a select of the form
768 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
769 // for 'x ? 2^n : 0' and fix the thing up at the end.
770 ConstantInt *Offset = nullptr;
771 if (!TrueVal->isZero() && !FalseVal->isZero()) {
772 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
773 Offset = FalseVal;
774 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
775 Offset = TrueVal;
776 else
777 return nullptr;
778
779 // Adjust TrueVal and FalseVal to the offset.
780 TrueVal = ConstantInt::get(Builder->getContext(),
781 TrueVal->getValue() - Offset->getValue());
782 FalseVal = ConstantInt::get(Builder->getContext(),
783 FalseVal->getValue() - Offset->getValue());
784 }
785
786 // Make sure the mask in the 'and' and one of the select arms is a power of 2.
787 if (!AndRHS->getValue().isPowerOf2() ||
788 (!TrueVal->getValue().isPowerOf2() &&
789 !FalseVal->getValue().isPowerOf2()))
790 return nullptr;
791
792 // Determine which shift is needed to transform result of the 'and' into the
793 // desired result.
794 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
795 unsigned ValZeros = ValC->getValue().logBase2();
796 unsigned AndZeros = AndRHS->getValue().logBase2();
797
798 // If types don't match we can still convert the select by introducing a zext
799 // or a trunc of the 'and'. The trunc case requires that all of the truncated
800 // bits are zero, we can figure that out by looking at the 'and' mask.
801 if (AndZeros >= ValC->getBitWidth())
802 return nullptr;
803
804 Value *V = Builder->CreateZExtOrTrunc(LHS, SI.getType());
805 if (ValZeros > AndZeros)
806 V = Builder->CreateShl(V, ValZeros - AndZeros);
807 else if (ValZeros < AndZeros)
808 V = Builder->CreateLShr(V, AndZeros - ValZeros);
809
810 // Okay, now we know that everything is set up, we just don't know whether we
811 // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
812 bool ShouldNotVal = !TrueVal->isZero();
813 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
814 if (ShouldNotVal)
815 V = Builder->CreateXor(V, ValC);
816
817 // Apply an offset if needed.
818 if (Offset)
819 V = Builder->CreateAdd(V, Offset);
820 return V;
821 }
822
visitSelectInst(SelectInst & SI)823 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
824 Value *CondVal = SI.getCondition();
825 Value *TrueVal = SI.getTrueValue();
826 Value *FalseVal = SI.getFalseValue();
827
828 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, DL))
829 return ReplaceInstUsesWith(SI, V);
830
831 if (SI.getType()->isIntegerTy(1)) {
832 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
833 if (C->getZExtValue()) {
834 // Change: A = select B, true, C --> A = or B, C
835 return BinaryOperator::CreateOr(CondVal, FalseVal);
836 }
837 // Change: A = select B, false, C --> A = and !B, C
838 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
839 return BinaryOperator::CreateAnd(NotCond, FalseVal);
840 }
841 if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
842 if (C->getZExtValue() == false) {
843 // Change: A = select B, C, false --> A = and B, C
844 return BinaryOperator::CreateAnd(CondVal, TrueVal);
845 }
846 // Change: A = select B, C, true --> A = or !B, C
847 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
848 return BinaryOperator::CreateOr(NotCond, TrueVal);
849 }
850
851 // select a, b, a -> a&b
852 // select a, a, b -> a|b
853 if (CondVal == TrueVal)
854 return BinaryOperator::CreateOr(CondVal, FalseVal);
855 if (CondVal == FalseVal)
856 return BinaryOperator::CreateAnd(CondVal, TrueVal);
857
858 // select a, ~a, b -> (~a)&b
859 // select a, b, ~a -> (~a)|b
860 if (match(TrueVal, m_Not(m_Specific(CondVal))))
861 return BinaryOperator::CreateAnd(TrueVal, FalseVal);
862 if (match(FalseVal, m_Not(m_Specific(CondVal))))
863 return BinaryOperator::CreateOr(TrueVal, FalseVal);
864 }
865
866 // Selecting between two integer constants?
867 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
868 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
869 // select C, 1, 0 -> zext C to int
870 if (FalseValC->isZero() && TrueValC->getValue() == 1)
871 return new ZExtInst(CondVal, SI.getType());
872
873 // select C, -1, 0 -> sext C to int
874 if (FalseValC->isZero() && TrueValC->isAllOnesValue())
875 return new SExtInst(CondVal, SI.getType());
876
877 // select C, 0, 1 -> zext !C to int
878 if (TrueValC->isZero() && FalseValC->getValue() == 1) {
879 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
880 return new ZExtInst(NotCond, SI.getType());
881 }
882
883 // select C, 0, -1 -> sext !C to int
884 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
885 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
886 return new SExtInst(NotCond, SI.getType());
887 }
888
889 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
890 return ReplaceInstUsesWith(SI, V);
891 }
892
893 // See if we are selecting two values based on a comparison of the two values.
894 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
895 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
896 // Transform (X == Y) ? X : Y -> Y
897 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
898 // This is not safe in general for floating point:
899 // consider X== -0, Y== +0.
900 // It becomes safe if either operand is a nonzero constant.
901 ConstantFP *CFPt, *CFPf;
902 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
903 !CFPt->getValueAPF().isZero()) ||
904 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
905 !CFPf->getValueAPF().isZero()))
906 return ReplaceInstUsesWith(SI, FalseVal);
907 }
908 // Transform (X une Y) ? X : Y -> X
909 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
910 // This is not safe in general for floating point:
911 // consider X== -0, Y== +0.
912 // It becomes safe if either operand is a nonzero constant.
913 ConstantFP *CFPt, *CFPf;
914 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
915 !CFPt->getValueAPF().isZero()) ||
916 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
917 !CFPf->getValueAPF().isZero()))
918 return ReplaceInstUsesWith(SI, TrueVal);
919 }
920 // NOTE: if we wanted to, this is where to detect MIN/MAX
921
922 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
923 // Transform (X == Y) ? Y : X -> X
924 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
925 // This is not safe in general for floating point:
926 // consider X== -0, Y== +0.
927 // It becomes safe if either operand is a nonzero constant.
928 ConstantFP *CFPt, *CFPf;
929 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
930 !CFPt->getValueAPF().isZero()) ||
931 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
932 !CFPf->getValueAPF().isZero()))
933 return ReplaceInstUsesWith(SI, FalseVal);
934 }
935 // Transform (X une Y) ? Y : X -> Y
936 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
937 // This is not safe in general for floating point:
938 // consider X== -0, Y== +0.
939 // It becomes safe if either operand is a nonzero constant.
940 ConstantFP *CFPt, *CFPf;
941 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
942 !CFPt->getValueAPF().isZero()) ||
943 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
944 !CFPf->getValueAPF().isZero()))
945 return ReplaceInstUsesWith(SI, TrueVal);
946 }
947 // NOTE: if we wanted to, this is where to detect MIN/MAX
948 }
949 // NOTE: if we wanted to, this is where to detect ABS
950 }
951
952 // See if we are selecting two values based on a comparison of the two values.
953 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
954 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
955 return Result;
956
957 if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
958 if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
959 if (TI->hasOneUse() && FI->hasOneUse()) {
960 Instruction *AddOp = nullptr, *SubOp = nullptr;
961
962 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
963 if (TI->getOpcode() == FI->getOpcode())
964 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
965 return IV;
966
967 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is
968 // even legal for FP.
969 if ((TI->getOpcode() == Instruction::Sub &&
970 FI->getOpcode() == Instruction::Add) ||
971 (TI->getOpcode() == Instruction::FSub &&
972 FI->getOpcode() == Instruction::FAdd)) {
973 AddOp = FI; SubOp = TI;
974 } else if ((FI->getOpcode() == Instruction::Sub &&
975 TI->getOpcode() == Instruction::Add) ||
976 (FI->getOpcode() == Instruction::FSub &&
977 TI->getOpcode() == Instruction::FAdd)) {
978 AddOp = TI; SubOp = FI;
979 }
980
981 if (AddOp) {
982 Value *OtherAddOp = nullptr;
983 if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
984 OtherAddOp = AddOp->getOperand(1);
985 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
986 OtherAddOp = AddOp->getOperand(0);
987 }
988
989 if (OtherAddOp) {
990 // So at this point we know we have (Y -> OtherAddOp):
991 // select C, (add X, Y), (sub X, Z)
992 Value *NegVal; // Compute -Z
993 if (SI.getType()->isFPOrFPVectorTy()) {
994 NegVal = Builder->CreateFNeg(SubOp->getOperand(1));
995 if (Instruction *NegInst = dyn_cast<Instruction>(NegVal)) {
996 FastMathFlags Flags = AddOp->getFastMathFlags();
997 Flags &= SubOp->getFastMathFlags();
998 NegInst->setFastMathFlags(Flags);
999 }
1000 } else {
1001 NegVal = Builder->CreateNeg(SubOp->getOperand(1));
1002 }
1003
1004 Value *NewTrueOp = OtherAddOp;
1005 Value *NewFalseOp = NegVal;
1006 if (AddOp != TI)
1007 std::swap(NewTrueOp, NewFalseOp);
1008 Value *NewSel =
1009 Builder->CreateSelect(CondVal, NewTrueOp,
1010 NewFalseOp, SI.getName() + ".p");
1011
1012 if (SI.getType()->isFPOrFPVectorTy()) {
1013 Instruction *RI =
1014 BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
1015
1016 FastMathFlags Flags = AddOp->getFastMathFlags();
1017 Flags &= SubOp->getFastMathFlags();
1018 RI->setFastMathFlags(Flags);
1019 return RI;
1020 } else
1021 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
1022 }
1023 }
1024 }
1025
1026 // See if we can fold the select into one of our operands.
1027 if (SI.getType()->isIntegerTy()) {
1028 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
1029 return FoldI;
1030
1031 // MAX(MAX(a, b), a) -> MAX(a, b)
1032 // MIN(MIN(a, b), a) -> MIN(a, b)
1033 // MAX(MIN(a, b), a) -> a
1034 // MIN(MAX(a, b), a) -> a
1035 Value *LHS, *RHS, *LHS2, *RHS2;
1036 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
1037 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
1038 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
1039 SI, SPF, RHS))
1040 return R;
1041 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
1042 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
1043 SI, SPF, LHS))
1044 return R;
1045 }
1046
1047 // TODO.
1048 // ABS(-X) -> ABS(X)
1049 }
1050
1051 // See if we can fold the select into a phi node if the condition is a select.
1052 if (isa<PHINode>(SI.getCondition()))
1053 // The true/false values have to be live in the PHI predecessor's blocks.
1054 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
1055 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
1056 if (Instruction *NV = FoldOpIntoPhi(SI))
1057 return NV;
1058
1059 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
1060 if (TrueSI->getCondition() == CondVal) {
1061 if (SI.getTrueValue() == TrueSI->getTrueValue())
1062 return nullptr;
1063 SI.setOperand(1, TrueSI->getTrueValue());
1064 return &SI;
1065 }
1066 }
1067 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
1068 if (FalseSI->getCondition() == CondVal) {
1069 if (SI.getFalseValue() == FalseSI->getFalseValue())
1070 return nullptr;
1071 SI.setOperand(2, FalseSI->getFalseValue());
1072 return &SI;
1073 }
1074 }
1075
1076 if (BinaryOperator::isNot(CondVal)) {
1077 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
1078 SI.setOperand(1, FalseVal);
1079 SI.setOperand(2, TrueVal);
1080 return &SI;
1081 }
1082
1083 if (VectorType* VecTy = dyn_cast<VectorType>(SI.getType())) {
1084 unsigned VWidth = VecTy->getNumElements();
1085 APInt UndefElts(VWidth, 0);
1086 APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
1087 if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
1088 if (V != &SI)
1089 return ReplaceInstUsesWith(SI, V);
1090 return &SI;
1091 }
1092
1093 if (isa<ConstantAggregateZero>(CondVal)) {
1094 return ReplaceInstUsesWith(SI, FalseVal);
1095 }
1096 }
1097
1098 return nullptr;
1099 }
1100