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1 //===- subzero/src/IceTargetLowering.cpp - Basic lowering implementation --===//
2 //
3 //                        The Subzero Code Generator
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 ///
10 /// \file
11 /// \brief Implements the skeleton of the TargetLowering class.
12 ///
13 /// Specifically this invokes the appropriate lowering method for a given
14 /// instruction kind and driving global register allocation. It also implements
15 /// the non-deleted instruction iteration in LoweringContext.
16 ///
17 //===----------------------------------------------------------------------===//
18 
19 #include "IceTargetLowering.h"
20 
21 #include "IceBitVector.h"
22 #include "IceCfg.h" // setError()
23 #include "IceCfgNode.h"
24 #include "IceGlobalContext.h"
25 #include "IceGlobalInits.h"
26 #include "IceInstVarIter.h"
27 #include "IceLiveness.h"
28 #include "IceOperand.h"
29 #include "IceRegAlloc.h"
30 
31 #include <string>
32 #include <vector>
33 
34 #define TARGET_LOWERING_CLASS_FOR(t) Target_##t
35 
36 // We prevent target-specific implementation details from leaking outside their
37 // implementations by forbidding #include of target-specific header files
38 // anywhere outside their own files. To create target-specific objects
39 // (TargetLowering, TargetDataLowering, and TargetHeaderLowering) we use the
40 // following named constructors. For reference, each target Foo needs to
41 // implement the following named constructors and initializer:
42 //
43 // namespace Foo {
44 //   unique_ptr<Ice::TargetLowering> createTargetLowering(Ice::Cfg *);
45 //   unique_ptr<Ice::TargetDataLowering>
46 //       createTargetDataLowering(Ice::GlobalContext*);
47 //   unique_ptr<Ice::TargetHeaderLowering>
48 //       createTargetHeaderLowering(Ice::GlobalContext *);
49 //   void staticInit(::Ice::GlobalContext *);
50 // }
51 #define SUBZERO_TARGET(X)                                                      \
52   namespace X {                                                                \
53   std::unique_ptr<::Ice::TargetLowering>                                       \
54   createTargetLowering(::Ice::Cfg *Func);                                      \
55   std::unique_ptr<::Ice::TargetDataLowering>                                   \
56   createTargetDataLowering(::Ice::GlobalContext *Ctx);                         \
57   std::unique_ptr<::Ice::TargetHeaderLowering>                                 \
58   createTargetHeaderLowering(::Ice::GlobalContext *Ctx);                       \
59   void staticInit(::Ice::GlobalContext *Ctx);                                  \
60   bool shouldBePooled(const ::Ice::Constant *C);                               \
61   ::Ice::Type getPointerType();                                                \
62   } // end of namespace X
63 #include "SZTargets.def"
64 #undef SUBZERO_TARGET
65 
66 namespace Ice {
init(CfgNode * N)67 void LoweringContext::init(CfgNode *N) {
68   Node = N;
69   End = getNode()->getInsts().end();
70   rewind();
71   advanceForward(Next);
72 }
73 
rewind()74 void LoweringContext::rewind() {
75   Begin = getNode()->getInsts().begin();
76   Cur = Begin;
77   skipDeleted(Cur);
78   Next = Cur;
79   availabilityReset();
80 }
81 
insert(Inst * Instr)82 void LoweringContext::insert(Inst *Instr) {
83   getNode()->getInsts().insert(Next, Instr);
84   LastInserted = Instr;
85 }
86 
skipDeleted(InstList::iterator & I) const87 void LoweringContext::skipDeleted(InstList::iterator &I) const {
88   while (I != End && I->isDeleted())
89     ++I;
90 }
91 
advanceForward(InstList::iterator & I) const92 void LoweringContext::advanceForward(InstList::iterator &I) const {
93   if (I != End) {
94     ++I;
95     skipDeleted(I);
96   }
97 }
98 
getLastInserted() const99 Inst *LoweringContext::getLastInserted() const {
100   assert(LastInserted);
101   return LastInserted;
102 }
103 
availabilityReset()104 void LoweringContext::availabilityReset() {
105   LastDest = nullptr;
106   LastSrc = nullptr;
107 }
108 
availabilityUpdate()109 void LoweringContext::availabilityUpdate() {
110   availabilityReset();
111   Inst *Instr = LastInserted;
112   if (Instr == nullptr)
113     return;
114   if (!Instr->isVarAssign())
115     return;
116   // Since isVarAssign() is true, the source operand must be a Variable.
117   LastDest = Instr->getDest();
118   LastSrc = llvm::cast<Variable>(Instr->getSrc(0));
119 }
120 
availabilityGet(Operand * Src) const121 Variable *LoweringContext::availabilityGet(Operand *Src) const {
122   assert(Src);
123   if (Src == LastDest)
124     return LastSrc;
125   return nullptr;
126 }
127 
128 namespace {
129 
printRegisterSet(Ostream & Str,const SmallBitVector & Bitset,std::function<std::string (RegNumT)> getRegName,const std::string & LineIndentString)130 void printRegisterSet(Ostream &Str, const SmallBitVector &Bitset,
131                       std::function<std::string(RegNumT)> getRegName,
132                       const std::string &LineIndentString) {
133   constexpr size_t RegistersPerLine = 16;
134   size_t Count = 0;
135   for (RegNumT RegNum : RegNumBVIter(Bitset)) {
136     if (Count == 0) {
137       Str << LineIndentString;
138     } else {
139       Str << ",";
140     }
141     if (Count > 0 && Count % RegistersPerLine == 0)
142       Str << "\n" << LineIndentString;
143     ++Count;
144     Str << getRegName(RegNum);
145   }
146   if (Count)
147     Str << "\n";
148 }
149 
150 // Splits "<class>:<reg>" into "<class>" plus "<reg>".  If there is no <class>
151 // component, the result is "" plus "<reg>".
splitToClassAndName(const std::string & RegName,std::string * SplitRegClass,std::string * SplitRegName)152 void splitToClassAndName(const std::string &RegName, std::string *SplitRegClass,
153                          std::string *SplitRegName) {
154   constexpr const char Separator[] = ":";
155   constexpr size_t SeparatorWidth = llvm::array_lengthof(Separator) - 1;
156   size_t Pos = RegName.find(Separator);
157   if (Pos == std::string::npos) {
158     *SplitRegClass = "";
159     *SplitRegName = RegName;
160   } else {
161     *SplitRegClass = RegName.substr(0, Pos);
162     *SplitRegName = RegName.substr(Pos + SeparatorWidth);
163   }
164 }
165 
badTargetFatalError(TargetArch Target)166 LLVM_ATTRIBUTE_NORETURN void badTargetFatalError(TargetArch Target) {
167   llvm::report_fatal_error("Unsupported target: " +
168                            std::string(targetArchString(Target)));
169 }
170 
171 } // end of anonymous namespace
172 
filterTypeToRegisterSet(GlobalContext * Ctx,int32_t NumRegs,SmallBitVector TypeToRegisterSet[],size_t TypeToRegisterSetSize,std::function<std::string (RegNumT)> getRegName,std::function<const char * (RegClass)> getRegClassName)173 void TargetLowering::filterTypeToRegisterSet(
174     GlobalContext *Ctx, int32_t NumRegs, SmallBitVector TypeToRegisterSet[],
175     size_t TypeToRegisterSetSize,
176     std::function<std::string(RegNumT)> getRegName,
177     std::function<const char *(RegClass)> getRegClassName) {
178   std::vector<SmallBitVector> UseSet(TypeToRegisterSetSize,
179                                      SmallBitVector(NumRegs));
180   std::vector<SmallBitVector> ExcludeSet(TypeToRegisterSetSize,
181                                          SmallBitVector(NumRegs));
182 
183   std::unordered_map<std::string, RegNumT> RegNameToIndex;
184   for (int32_t RegIndex = 0; RegIndex < NumRegs; ++RegIndex) {
185     const auto RegNum = RegNumT::fromInt(RegIndex);
186     RegNameToIndex[getRegName(RegNum)] = RegNum;
187   }
188 
189   std::vector<std::string> BadRegNames;
190 
191   // The processRegList function iterates across the RegNames vector.  Each
192   // entry in the vector is a string of the form "<reg>" or "<class>:<reg>".
193   // The register class and register number are computed, and the corresponding
194   // bit is set in RegSet[][].  If "<class>:" is missing, then the bit is set
195   // for all classes.
196   auto processRegList = [&](const std::vector<std::string> &RegNames,
197                             std::vector<SmallBitVector> &RegSet) {
198     for (const std::string &RegClassAndName : RegNames) {
199       std::string RClass;
200       std::string RName;
201       splitToClassAndName(RegClassAndName, &RClass, &RName);
202       if (!RegNameToIndex.count(RName)) {
203         BadRegNames.push_back(RName);
204         continue;
205       }
206       const int32_t RegIndex = RegNameToIndex.at(RName);
207       for (SizeT TypeIndex = 0; TypeIndex < TypeToRegisterSetSize;
208            ++TypeIndex) {
209         if (RClass.empty() ||
210             RClass == getRegClassName(static_cast<RegClass>(TypeIndex))) {
211           RegSet[TypeIndex][RegIndex] = TypeToRegisterSet[TypeIndex][RegIndex];
212         }
213       }
214     }
215   };
216 
217   processRegList(getFlags().getUseRestrictedRegisters(), UseSet);
218   processRegList(getFlags().getExcludedRegisters(), ExcludeSet);
219 
220   if (!BadRegNames.empty()) {
221     std::string Buffer;
222     llvm::raw_string_ostream StrBuf(Buffer);
223     StrBuf << "Unrecognized use/exclude registers:";
224     for (const auto &RegName : BadRegNames)
225       StrBuf << " " << RegName;
226     llvm::report_fatal_error(StrBuf.str());
227   }
228 
229   // Apply filters.
230   for (size_t TypeIndex = 0; TypeIndex < TypeToRegisterSetSize; ++TypeIndex) {
231     SmallBitVector *TypeBitSet = &TypeToRegisterSet[TypeIndex];
232     SmallBitVector *UseBitSet = &UseSet[TypeIndex];
233     SmallBitVector *ExcludeBitSet = &ExcludeSet[TypeIndex];
234     if (UseBitSet->any())
235       *TypeBitSet = *UseBitSet;
236     (*TypeBitSet).reset(*ExcludeBitSet);
237   }
238 
239   // Display filtered register sets, if requested.
240   if (BuildDefs::dump() && NumRegs &&
241       (getFlags().getVerbose() & IceV_AvailableRegs)) {
242     Ostream &Str = Ctx->getStrDump();
243     const std::string Indent = "  ";
244     const std::string IndentTwice = Indent + Indent;
245     Str << "Registers available for register allocation:\n";
246     for (size_t TypeIndex = 0; TypeIndex < TypeToRegisterSetSize; ++TypeIndex) {
247       Str << Indent << getRegClassName(static_cast<RegClass>(TypeIndex))
248           << ":\n";
249       printRegisterSet(Str, TypeToRegisterSet[TypeIndex], getRegName,
250                        IndentTwice);
251     }
252     Str << "\n";
253   }
254 }
255 
256 std::unique_ptr<TargetLowering>
createLowering(TargetArch Target,Cfg * Func)257 TargetLowering::createLowering(TargetArch Target, Cfg *Func) {
258   switch (Target) {
259   default:
260     badTargetFatalError(Target);
261 #define SUBZERO_TARGET(X)                                                      \
262   case TARGET_LOWERING_CLASS_FOR(X):                                           \
263     return ::X::createTargetLowering(Func);
264 #include "SZTargets.def"
265 #undef SUBZERO_TARGET
266   }
267 }
268 
staticInit(GlobalContext * Ctx)269 void TargetLowering::staticInit(GlobalContext *Ctx) {
270   const TargetArch Target = getFlags().getTargetArch();
271   // Call the specified target's static initializer.
272   switch (Target) {
273   default:
274     badTargetFatalError(Target);
275 #define SUBZERO_TARGET(X)                                                      \
276   case TARGET_LOWERING_CLASS_FOR(X): {                                         \
277     static bool InitGuard##X = false;                                          \
278     if (InitGuard##X) {                                                        \
279       return;                                                                  \
280     }                                                                          \
281     InitGuard##X = true;                                                       \
282     ::X::staticInit(Ctx);                                                      \
283   } break;
284 #include "SZTargets.def"
285 #undef SUBZERO_TARGET
286   }
287 }
288 
shouldBePooled(const Constant * C)289 bool TargetLowering::shouldBePooled(const Constant *C) {
290   const TargetArch Target = getFlags().getTargetArch();
291   switch (Target) {
292   default:
293     return false;
294 #define SUBZERO_TARGET(X)                                                      \
295   case TARGET_LOWERING_CLASS_FOR(X):                                           \
296     return ::X::shouldBePooled(C);
297 #include "SZTargets.def"
298 #undef SUBZERO_TARGET
299   }
300 }
301 
getPointerType()302 ::Ice::Type TargetLowering::getPointerType() {
303   const TargetArch Target = getFlags().getTargetArch();
304   switch (Target) {
305   default:
306     return ::Ice::IceType_void;
307 #define SUBZERO_TARGET(X)                                                      \
308   case TARGET_LOWERING_CLASS_FOR(X):                                           \
309     return ::X::getPointerType();
310 #include "SZTargets.def"
311 #undef SUBZERO_TARGET
312   }
313 }
314 
315 TargetLowering::SandboxType
determineSandboxTypeFromFlags(const ClFlags & Flags)316 TargetLowering::determineSandboxTypeFromFlags(const ClFlags &Flags) {
317   assert(!Flags.getUseSandboxing() || !Flags.getUseNonsfi());
318   if (Flags.getUseNonsfi()) {
319     return TargetLowering::ST_Nonsfi;
320   }
321   if (Flags.getUseSandboxing()) {
322     return TargetLowering::ST_NaCl;
323   }
324   return TargetLowering::ST_None;
325 }
326 
TargetLowering(Cfg * Func)327 TargetLowering::TargetLowering(Cfg *Func)
328     : Func(Func), Ctx(Func->getContext()),
329       SandboxingType(determineSandboxTypeFromFlags(getFlags())) {}
330 
AutoBundle(TargetLowering * Target,InstBundleLock::Option Option)331 TargetLowering::AutoBundle::AutoBundle(TargetLowering *Target,
332                                        InstBundleLock::Option Option)
333     : Target(Target), NeedSandboxing(getFlags().getUseSandboxing()) {
334   assert(!Target->AutoBundling);
335   Target->AutoBundling = true;
336   if (NeedSandboxing) {
337     Target->_bundle_lock(Option);
338   }
339 }
340 
~AutoBundle()341 TargetLowering::AutoBundle::~AutoBundle() {
342   assert(Target->AutoBundling);
343   Target->AutoBundling = false;
344   if (NeedSandboxing) {
345     Target->_bundle_unlock();
346   }
347 }
348 
genTargetHelperCalls()349 void TargetLowering::genTargetHelperCalls() {
350   TimerMarker T(TimerStack::TT_genHelpers, Func);
351   Utils::BoolFlagSaver _(GeneratingTargetHelpers, true);
352   for (CfgNode *Node : Func->getNodes()) {
353     Context.init(Node);
354     while (!Context.atEnd()) {
355       PostIncrLoweringContext _(Context);
356       genTargetHelperCallFor(iteratorToInst(Context.getCur()));
357     }
358   }
359 }
360 
doAddressOpt()361 void TargetLowering::doAddressOpt() {
362   doAddressOptOther();
363   if (llvm::isa<InstLoad>(*Context.getCur()))
364     doAddressOptLoad();
365   else if (llvm::isa<InstStore>(*Context.getCur()))
366     doAddressOptStore();
367   else if (auto *Intrinsic =
368                llvm::dyn_cast<InstIntrinsic>(&*Context.getCur())) {
369     if (Intrinsic->getIntrinsicID() == Intrinsics::LoadSubVector)
370       doAddressOptLoadSubVector();
371     else if (Intrinsic->getIntrinsicID() == Intrinsics::StoreSubVector)
372       doAddressOptStoreSubVector();
373   }
374   Context.advanceCur();
375   Context.advanceNext();
376 }
377 
378 // Lowers a single instruction according to the information in Context, by
379 // checking the Context.Cur instruction kind and calling the appropriate
380 // lowering method. The lowering method should insert target instructions at
381 // the Cur.Next insertion point, and should not delete the Context.Cur
382 // instruction or advance Context.Cur.
383 //
384 // The lowering method may look ahead in the instruction stream as desired, and
385 // lower additional instructions in conjunction with the current one, for
386 // example fusing a compare and branch. If it does, it should advance
387 // Context.Cur to point to the next non-deleted instruction to process, and it
388 // should delete any additional instructions it consumes.
lower()389 void TargetLowering::lower() {
390   assert(!Context.atEnd());
391   Inst *Instr = iteratorToInst(Context.getCur());
392   Instr->deleteIfDead();
393   if (!Instr->isDeleted() && !llvm::isa<InstFakeDef>(Instr) &&
394       !llvm::isa<InstFakeUse>(Instr)) {
395     // Mark the current instruction as deleted before lowering, otherwise the
396     // Dest variable will likely get marked as non-SSA. See
397     // Variable::setDefinition(). However, just pass-through FakeDef and
398     // FakeUse instructions that might have been inserted prior to lowering.
399     Instr->setDeleted();
400     switch (Instr->getKind()) {
401     case Inst::Alloca:
402       lowerAlloca(llvm::cast<InstAlloca>(Instr));
403       break;
404     case Inst::Arithmetic:
405       lowerArithmetic(llvm::cast<InstArithmetic>(Instr));
406       break;
407     case Inst::Assign:
408       lowerAssign(llvm::cast<InstAssign>(Instr));
409       break;
410     case Inst::Br:
411       lowerBr(llvm::cast<InstBr>(Instr));
412       break;
413     case Inst::Breakpoint:
414       lowerBreakpoint(llvm::cast<InstBreakpoint>(Instr));
415       break;
416     case Inst::Call:
417       lowerCall(llvm::cast<InstCall>(Instr));
418       break;
419     case Inst::Cast:
420       lowerCast(llvm::cast<InstCast>(Instr));
421       break;
422     case Inst::ExtractElement:
423       lowerExtractElement(llvm::cast<InstExtractElement>(Instr));
424       break;
425     case Inst::Fcmp:
426       lowerFcmp(llvm::cast<InstFcmp>(Instr));
427       break;
428     case Inst::Icmp:
429       lowerIcmp(llvm::cast<InstIcmp>(Instr));
430       break;
431     case Inst::InsertElement:
432       lowerInsertElement(llvm::cast<InstInsertElement>(Instr));
433       break;
434     case Inst::Intrinsic: {
435       auto *Intrinsic = llvm::cast<InstIntrinsic>(Instr);
436       if (Intrinsic->getIntrinsicInfo().ReturnsTwice)
437         setCallsReturnsTwice(true);
438       lowerIntrinsic(Intrinsic);
439       break;
440     }
441     case Inst::Load:
442       lowerLoad(llvm::cast<InstLoad>(Instr));
443       break;
444     case Inst::Phi:
445       lowerPhi(llvm::cast<InstPhi>(Instr));
446       break;
447     case Inst::Ret:
448       lowerRet(llvm::cast<InstRet>(Instr));
449       break;
450     case Inst::Select:
451       lowerSelect(llvm::cast<InstSelect>(Instr));
452       break;
453     case Inst::ShuffleVector:
454       lowerShuffleVector(llvm::cast<InstShuffleVector>(Instr));
455       break;
456     case Inst::Store:
457       lowerStore(llvm::cast<InstStore>(Instr));
458       break;
459     case Inst::Switch:
460       lowerSwitch(llvm::cast<InstSwitch>(Instr));
461       break;
462     case Inst::Unreachable:
463       lowerUnreachable(llvm::cast<InstUnreachable>(Instr));
464       break;
465     default:
466       lowerOther(Instr);
467       break;
468     }
469 
470     postLower();
471   }
472 
473   Context.advanceCur();
474   Context.advanceNext();
475 }
476 
lowerInst(CfgNode * Node,InstList::iterator Next,InstHighLevel * Instr)477 void TargetLowering::lowerInst(CfgNode *Node, InstList::iterator Next,
478                                InstHighLevel *Instr) {
479   // TODO(stichnot): Consider modifying the design/implementation to avoid
480   // multiple init() calls when using lowerInst() to lower several instructions
481   // in the same node.
482   Context.init(Node);
483   Context.setNext(Next);
484   Context.insert(Instr);
485   --Next;
486   assert(iteratorToInst(Next) == Instr);
487   Context.setCur(Next);
488   lower();
489 }
490 
lowerOther(const Inst * Instr)491 void TargetLowering::lowerOther(const Inst *Instr) {
492   (void)Instr;
493   Func->setError("Can't lower unsupported instruction type");
494 }
495 
496 // Drives register allocation, allowing all physical registers (except perhaps
497 // for the frame pointer) to be allocated. This set of registers could
498 // potentially be parameterized if we want to restrict registers e.g. for
499 // performance testing.
regAlloc(RegAllocKind Kind)500 void TargetLowering::regAlloc(RegAllocKind Kind) {
501   TimerMarker T(TimerStack::TT_regAlloc, Func);
502   LinearScan LinearScan(Func);
503   RegSetMask RegInclude = RegSet_None;
504   RegSetMask RegExclude = RegSet_None;
505   RegInclude |= RegSet_CallerSave;
506   RegInclude |= RegSet_CalleeSave;
507   if (hasFramePointer())
508     RegExclude |= RegSet_FramePointer;
509   SmallBitVector RegMask = getRegisterSet(RegInclude, RegExclude);
510   bool Repeat = (Kind == RAK_Global && getFlags().getRepeatRegAlloc());
511   CfgSet<Variable *> EmptySet;
512   do {
513     LinearScan.init(Kind, EmptySet);
514     LinearScan.scan(RegMask);
515     if (!LinearScan.hasEvictions())
516       Repeat = false;
517     Kind = RAK_SecondChance;
518   } while (Repeat);
519   // TODO(stichnot): Run the register allocator one more time to do stack slot
520   // coalescing.  The idea would be to initialize the Unhandled list with the
521   // set of Variables that have no register and a non-empty live range, and
522   // model an infinite number of registers.  Maybe use the register aliasing
523   // mechanism to get better packing of narrower slots.
524   if (getFlags().getSplitGlobalVars())
525     postRegallocSplitting(RegMask);
526 }
527 
528 namespace {
getInstructionsInRange(CfgNode * Node,InstNumberT Start,InstNumberT End)529 CfgVector<Inst *> getInstructionsInRange(CfgNode *Node, InstNumberT Start,
530                                          InstNumberT End) {
531   CfgVector<Inst *> Result;
532   bool Started = false;
533   auto Process = [&](InstList &Insts) {
534     for (auto &Instr : Insts) {
535       if (Instr.isDeleted()) {
536         continue;
537       }
538       if (Instr.getNumber() == Start) {
539         Started = true;
540       }
541       if (Started) {
542         Result.emplace_back(&Instr);
543       }
544       if (Instr.getNumber() == End) {
545         break;
546       }
547     }
548   };
549   Process(Node->getPhis());
550   Process(Node->getInsts());
551   // TODO(manasijm): Investigate why checking >= End significantly changes
552   // output. Should not happen when renumbering produces monotonically
553   // increasing instruction numbers and live ranges begin and end on non-deleted
554   // instructions.
555   return Result;
556 }
557 } // namespace
558 
postRegallocSplitting(const SmallBitVector & RegMask)559 void TargetLowering::postRegallocSplitting(const SmallBitVector &RegMask) {
560   // Splits the live ranges of global(/multi block) variables and runs the
561   // register allocator to find registers for as many of the new variables as
562   // possible.
563   // TODO(manasijm): Merge the small liveranges back into multi-block ones when
564   // the variables get the same register. This will reduce the amount of new
565   // instructions inserted. This might involve a full dataflow analysis.
566   // Also, modify the preference mechanism in the register allocator to match.
567 
568   TimerMarker _(TimerStack::TT_splitGlobalVars, Func);
569   CfgSet<Variable *> SplitCandidates;
570 
571   // Find variables that do not have registers but are allowed to. Also skip
572   // variables with single segment live ranges as they are not split further in
573   // this function.
574   for (Variable *Var : Func->getVariables()) {
575     if (!Var->mustNotHaveReg() && !Var->hasReg()) {
576       if (Var->getLiveRange().getNumSegments() > 1)
577         SplitCandidates.insert(Var);
578     }
579   }
580   if (SplitCandidates.empty())
581     return;
582 
583   CfgSet<Variable *> ExtraVars;
584 
585   struct UseInfo {
586     Variable *Replacing = nullptr;
587     Inst *FirstUse = nullptr;
588     Inst *LastDef = nullptr;
589     SizeT UseCount = 0;
590   };
591   CfgUnorderedMap<Variable *, UseInfo> VarInfo;
592   // Split the live ranges of the viable variables by node.
593   // Compute metadata (UseInfo) for each of the resulting variables.
594   for (auto *Var : SplitCandidates) {
595     for (auto &Segment : Var->getLiveRange().getSegments()) {
596       UseInfo Info;
597       Info.Replacing = Var;
598       auto *Node = Var->getLiveRange().getNodeForSegment(Segment.first);
599 
600       for (auto *Instr :
601            getInstructionsInRange(Node, Segment.first, Segment.second)) {
602         for (SizeT i = 0; i < Instr->getSrcSize(); ++i) {
603           // It's safe to iterate over the top-level src operands rather than
604           // using FOREACH_VAR_IN_INST(), because any variables inside e.g.
605           // mem operands should already have registers.
606           if (auto *Var = llvm::dyn_cast<Variable>(Instr->getSrc(i))) {
607             if (Var == Info.Replacing) {
608               if (Info.FirstUse == nullptr && !llvm::isa<InstPhi>(Instr)) {
609                 Info.FirstUse = Instr;
610               }
611               Info.UseCount++;
612             }
613           }
614         }
615         if (Instr->getDest() == Info.Replacing && !llvm::isa<InstPhi>(Instr)) {
616           Info.LastDef = Instr;
617         }
618       }
619 
620       static constexpr SizeT MinUseThreshold = 3;
621       // Skip if variable has less than `MinUseThreshold` uses in the segment.
622       if (Info.UseCount < MinUseThreshold)
623         continue;
624 
625       if (!Info.FirstUse && !Info.LastDef) {
626         continue;
627       }
628 
629       LiveRange LR;
630       LR.addSegment(Segment);
631       Variable *NewVar = Func->makeVariable(Var->getType());
632 
633       NewVar->setLiveRange(LR);
634 
635       VarInfo[NewVar] = Info;
636 
637       ExtraVars.insert(NewVar);
638     }
639   }
640   // Run the register allocator with all these new variables included
641   LinearScan RegAlloc(Func);
642   RegAlloc.init(RAK_Global, SplitCandidates);
643   RegAlloc.scan(RegMask);
644 
645   // Modify the Cfg to use the new variables that now have registers.
646   for (auto *ExtraVar : ExtraVars) {
647     if (!ExtraVar->hasReg()) {
648       continue;
649     }
650 
651     auto &Info = VarInfo[ExtraVar];
652 
653     assert(ExtraVar->getLiveRange().getSegments().size() == 1);
654     auto Segment = ExtraVar->getLiveRange().getSegments()[0];
655 
656     auto *Node =
657         Info.Replacing->getLiveRange().getNodeForSegment(Segment.first);
658 
659     auto RelevantInsts =
660         getInstructionsInRange(Node, Segment.first, Segment.second);
661 
662     if (RelevantInsts.empty())
663       continue;
664 
665     // Replace old variables
666     for (auto *Instr : RelevantInsts) {
667       if (llvm::isa<InstPhi>(Instr))
668         continue;
669       // TODO(manasijm): Figure out how to safely enable replacing phi dest
670       // variables. The issue is that we can not insert low level mov
671       // instructions into the PhiList.
672       for (SizeT i = 0; i < Instr->getSrcSize(); ++i) {
673         // FOREACH_VAR_IN_INST() not needed. Same logic as above.
674         if (auto *Var = llvm::dyn_cast<Variable>(Instr->getSrc(i))) {
675           if (Var == Info.Replacing) {
676             Instr->replaceSource(i, ExtraVar);
677           }
678         }
679       }
680       if (Instr->getDest() == Info.Replacing) {
681         Instr->replaceDest(ExtraVar);
682       }
683     }
684 
685     assert(Info.FirstUse != Info.LastDef);
686     assert(Info.FirstUse || Info.LastDef);
687 
688     // Insert spill code
689     if (Info.FirstUse != nullptr) {
690       auto *NewInst =
691           Func->getTarget()->createLoweredMove(ExtraVar, Info.Replacing);
692       Node->getInsts().insert(instToIterator(Info.FirstUse), NewInst);
693     }
694     if (Info.LastDef != nullptr) {
695       auto *NewInst =
696           Func->getTarget()->createLoweredMove(Info.Replacing, ExtraVar);
697       Node->getInsts().insertAfter(instToIterator(Info.LastDef), NewInst);
698     }
699   }
700 }
701 
markRedefinitions()702 void TargetLowering::markRedefinitions() {
703   // Find (non-SSA) instructions where the Dest variable appears in some source
704   // operand, and set the IsDestRedefined flag to keep liveness analysis
705   // consistent.
706   for (auto Instr = Context.getCur(), E = Context.getNext(); Instr != E;
707        ++Instr) {
708     if (Instr->isDeleted())
709       continue;
710     Variable *Dest = Instr->getDest();
711     if (Dest == nullptr)
712       continue;
713     FOREACH_VAR_IN_INST(Var, *Instr) {
714       if (Var == Dest) {
715         Instr->setDestRedefined();
716         break;
717       }
718     }
719   }
720 }
721 
addFakeDefUses(const Inst * Instr)722 void TargetLowering::addFakeDefUses(const Inst *Instr) {
723   FOREACH_VAR_IN_INST(Var, *Instr) {
724     if (auto *Var64 = llvm::dyn_cast<Variable64On32>(Var)) {
725       Context.insert<InstFakeUse>(Var64->getLo());
726       Context.insert<InstFakeUse>(Var64->getHi());
727     } else if (auto *VarVec = llvm::dyn_cast<VariableVecOn32>(Var)) {
728       for (Variable *Var : VarVec->getContainers()) {
729         Context.insert<InstFakeUse>(Var);
730       }
731     } else {
732       Context.insert<InstFakeUse>(Var);
733     }
734   }
735   Variable *Dest = Instr->getDest();
736   if (Dest == nullptr)
737     return;
738   if (auto *Var64 = llvm::dyn_cast<Variable64On32>(Dest)) {
739     Context.insert<InstFakeDef>(Var64->getLo());
740     Context.insert<InstFakeDef>(Var64->getHi());
741   } else if (auto *VarVec = llvm::dyn_cast<VariableVecOn32>(Dest)) {
742     for (Variable *Var : VarVec->getContainers()) {
743       Context.insert<InstFakeDef>(Var);
744     }
745   } else {
746     Context.insert<InstFakeDef>(Dest);
747   }
748 }
749 
sortVarsByAlignment(VarList & Dest,const VarList & Source) const750 void TargetLowering::sortVarsByAlignment(VarList &Dest,
751                                          const VarList &Source) const {
752   Dest = Source;
753   // Instead of std::sort, we could do a bucket sort with log2(alignment) as
754   // the buckets, if performance is an issue.
755   std::sort(Dest.begin(), Dest.end(),
756             [this](const Variable *V1, const Variable *V2) {
757               const size_t WidthV1 = typeWidthInBytesOnStack(V1->getType());
758               const size_t WidthV2 = typeWidthInBytesOnStack(V2->getType());
759               if (WidthV1 == WidthV2)
760                 return V1->getIndex() < V2->getIndex();
761               return WidthV1 > WidthV2;
762             });
763 }
764 
getVarStackSlotParams(VarList & SortedSpilledVariables,SmallBitVector & RegsUsed,size_t * GlobalsSize,size_t * SpillAreaSizeBytes,uint32_t * SpillAreaAlignmentBytes,uint32_t * LocalsSlotsAlignmentBytes,std::function<bool (Variable *)> TargetVarHook)765 void TargetLowering::getVarStackSlotParams(
766     VarList &SortedSpilledVariables, SmallBitVector &RegsUsed,
767     size_t *GlobalsSize, size_t *SpillAreaSizeBytes,
768     uint32_t *SpillAreaAlignmentBytes, uint32_t *LocalsSlotsAlignmentBytes,
769     std::function<bool(Variable *)> TargetVarHook) {
770   const VariablesMetadata *VMetadata = Func->getVMetadata();
771   BitVector IsVarReferenced(Func->getNumVariables());
772   for (CfgNode *Node : Func->getNodes()) {
773     for (Inst &Instr : Node->getInsts()) {
774       if (Instr.isDeleted())
775         continue;
776       if (const Variable *Var = Instr.getDest())
777         IsVarReferenced[Var->getIndex()] = true;
778       FOREACH_VAR_IN_INST(Var, Instr) {
779         IsVarReferenced[Var->getIndex()] = true;
780       }
781     }
782   }
783 
784   // If SimpleCoalescing is false, each variable without a register gets its
785   // own unique stack slot, which leads to large stack frames. If
786   // SimpleCoalescing is true, then each "global" variable without a register
787   // gets its own slot, but "local" variable slots are reused across basic
788   // blocks. E.g., if A and B are local to block 1 and C is local to block 2,
789   // then C may share a slot with A or B.
790   //
791   // We cannot coalesce stack slots if this function calls a "returns twice"
792   // function. In that case, basic blocks may be revisited, and variables local
793   // to those basic blocks are actually live until after the called function
794   // returns a second time.
795   const bool SimpleCoalescing = !callsReturnsTwice();
796 
797   CfgVector<size_t> LocalsSize(Func->getNumNodes());
798   const VarList &Variables = Func->getVariables();
799   VarList SpilledVariables;
800   for (Variable *Var : Variables) {
801     if (Var->hasReg()) {
802       // Don't consider a rematerializable variable to be an actual register use
803       // (specifically of the frame pointer).  Otherwise, the prolog may decide
804       // to save the frame pointer twice - once because of the explicit need for
805       // a frame pointer, and once because of an active use of a callee-save
806       // register.
807       if (!Var->isRematerializable())
808         RegsUsed[Var->getRegNum()] = true;
809       continue;
810     }
811     // An argument either does not need a stack slot (if passed in a register)
812     // or already has one (if passed on the stack).
813     if (Var->getIsArg()) {
814       if (!Var->hasReg()) {
815         assert(!Var->hasStackOffset());
816         Var->setHasStackOffset();
817       }
818       continue;
819     }
820     // An unreferenced variable doesn't need a stack slot.
821     if (!IsVarReferenced[Var->getIndex()])
822       continue;
823     // Check a target-specific variable (it may end up sharing stack slots) and
824     // not need accounting here.
825     if (TargetVarHook(Var))
826       continue;
827     assert(!Var->hasStackOffset());
828     Var->setHasStackOffset();
829     SpilledVariables.push_back(Var);
830   }
831 
832   SortedSpilledVariables.reserve(SpilledVariables.size());
833   sortVarsByAlignment(SortedSpilledVariables, SpilledVariables);
834 
835   for (Variable *Var : SortedSpilledVariables) {
836     size_t Increment = typeWidthInBytesOnStack(Var->getType());
837     // We have sorted by alignment, so the first variable we encounter that is
838     // located in each area determines the max alignment for the area.
839     if (!*SpillAreaAlignmentBytes)
840       *SpillAreaAlignmentBytes = Increment;
841     if (SimpleCoalescing && VMetadata->isTracked(Var)) {
842       if (VMetadata->isMultiBlock(Var)) {
843         *GlobalsSize += Increment;
844       } else {
845         SizeT NodeIndex = VMetadata->getLocalUseNode(Var)->getIndex();
846         LocalsSize[NodeIndex] += Increment;
847         if (LocalsSize[NodeIndex] > *SpillAreaSizeBytes)
848           *SpillAreaSizeBytes = LocalsSize[NodeIndex];
849         if (!*LocalsSlotsAlignmentBytes)
850           *LocalsSlotsAlignmentBytes = Increment;
851       }
852     } else {
853       *SpillAreaSizeBytes += Increment;
854     }
855   }
856   // For testing legalization of large stack offsets on targets with limited
857   // offset bits in instruction encodings, add some padding.
858   *SpillAreaSizeBytes += getFlags().getTestStackExtra();
859 }
860 
alignStackSpillAreas(uint32_t SpillAreaStartOffset,uint32_t SpillAreaAlignmentBytes,size_t GlobalsSize,uint32_t LocalsSlotsAlignmentBytes,uint32_t * SpillAreaPaddingBytes,uint32_t * LocalsSlotsPaddingBytes)861 void TargetLowering::alignStackSpillAreas(uint32_t SpillAreaStartOffset,
862                                           uint32_t SpillAreaAlignmentBytes,
863                                           size_t GlobalsSize,
864                                           uint32_t LocalsSlotsAlignmentBytes,
865                                           uint32_t *SpillAreaPaddingBytes,
866                                           uint32_t *LocalsSlotsPaddingBytes) {
867   if (SpillAreaAlignmentBytes) {
868     uint32_t PaddingStart = SpillAreaStartOffset;
869     uint32_t SpillAreaStart =
870         Utils::applyAlignment(PaddingStart, SpillAreaAlignmentBytes);
871     *SpillAreaPaddingBytes = SpillAreaStart - PaddingStart;
872   }
873 
874   // If there are separate globals and locals areas, make sure the locals area
875   // is aligned by padding the end of the globals area.
876   if (LocalsSlotsAlignmentBytes) {
877     uint32_t GlobalsAndSubsequentPaddingSize = GlobalsSize;
878     GlobalsAndSubsequentPaddingSize =
879         Utils::applyAlignment(GlobalsSize, LocalsSlotsAlignmentBytes);
880     *LocalsSlotsPaddingBytes = GlobalsAndSubsequentPaddingSize - GlobalsSize;
881   }
882 }
883 
assignVarStackSlots(VarList & SortedSpilledVariables,size_t SpillAreaPaddingBytes,size_t SpillAreaSizeBytes,size_t GlobalsAndSubsequentPaddingSize,bool UsesFramePointer)884 void TargetLowering::assignVarStackSlots(VarList &SortedSpilledVariables,
885                                          size_t SpillAreaPaddingBytes,
886                                          size_t SpillAreaSizeBytes,
887                                          size_t GlobalsAndSubsequentPaddingSize,
888                                          bool UsesFramePointer) {
889   const VariablesMetadata *VMetadata = Func->getVMetadata();
890   // For testing legalization of large stack offsets on targets with limited
891   // offset bits in instruction encodings, add some padding. This assumes that
892   // SpillAreaSizeBytes has accounted for the extra test padding. When
893   // UseFramePointer is true, the offset depends on the padding, not just the
894   // SpillAreaSizeBytes. On the other hand, when UseFramePointer is false, the
895   // offsets depend on the gap between SpillAreaSizeBytes and
896   // SpillAreaPaddingBytes, so we don't increment that.
897   size_t TestPadding = getFlags().getTestStackExtra();
898   if (UsesFramePointer)
899     SpillAreaPaddingBytes += TestPadding;
900   size_t GlobalsSpaceUsed = SpillAreaPaddingBytes;
901   size_t NextStackOffset = SpillAreaPaddingBytes;
902   CfgVector<size_t> LocalsSize(Func->getNumNodes());
903   const bool SimpleCoalescing = !callsReturnsTwice();
904 
905   for (Variable *Var : SortedSpilledVariables) {
906     size_t Increment = typeWidthInBytesOnStack(Var->getType());
907     if (SimpleCoalescing && VMetadata->isTracked(Var)) {
908       if (VMetadata->isMultiBlock(Var)) {
909         GlobalsSpaceUsed += Increment;
910         NextStackOffset = GlobalsSpaceUsed;
911       } else {
912         SizeT NodeIndex = VMetadata->getLocalUseNode(Var)->getIndex();
913         LocalsSize[NodeIndex] += Increment;
914         NextStackOffset = SpillAreaPaddingBytes +
915                           GlobalsAndSubsequentPaddingSize +
916                           LocalsSize[NodeIndex];
917       }
918     } else {
919       NextStackOffset += Increment;
920     }
921     if (UsesFramePointer)
922       Var->setStackOffset(-NextStackOffset);
923     else
924       Var->setStackOffset(SpillAreaSizeBytes - NextStackOffset);
925   }
926 }
927 
makeHelperCall(RuntimeHelper FuncID,Variable * Dest,SizeT MaxSrcs)928 InstCall *TargetLowering::makeHelperCall(RuntimeHelper FuncID, Variable *Dest,
929                                          SizeT MaxSrcs) {
930   constexpr bool HasTailCall = false;
931   Constant *CallTarget = Ctx->getRuntimeHelperFunc(FuncID);
932   InstCall *Call =
933       InstCall::create(Func, MaxSrcs, Dest, CallTarget, HasTailCall);
934   return Call;
935 }
936 
shouldOptimizeMemIntrins()937 bool TargetLowering::shouldOptimizeMemIntrins() {
938   return Func->getOptLevel() >= Opt_1 || getFlags().getForceMemIntrinOpt();
939 }
940 
scalarizeArithmetic(InstArithmetic::OpKind Kind,Variable * Dest,Operand * Src0,Operand * Src1)941 void TargetLowering::scalarizeArithmetic(InstArithmetic::OpKind Kind,
942                                          Variable *Dest, Operand *Src0,
943                                          Operand *Src1) {
944   scalarizeInstruction(
945       Dest,
946       [this, Kind](Variable *Dest, Operand *Src0, Operand *Src1) {
947         return Context.insert<InstArithmetic>(Kind, Dest, Src0, Src1);
948       },
949       Src0, Src1);
950 }
951 
emitWithoutPrefix(const ConstantRelocatable * C,const char * Suffix) const952 void TargetLowering::emitWithoutPrefix(const ConstantRelocatable *C,
953                                        const char *Suffix) const {
954   if (!BuildDefs::dump())
955     return;
956   Ostream &Str = Ctx->getStrEmit();
957   const std::string &EmitStr = C->getEmitString();
958   if (!EmitStr.empty()) {
959     // C has a custom emit string, so we use it instead of the canonical
960     // Name + Offset form.
961     Str << EmitStr;
962     return;
963   }
964   Str << C->getName() << Suffix;
965   RelocOffsetT Offset = C->getOffset();
966   if (Offset) {
967     if (Offset > 0)
968       Str << "+";
969     Str << Offset;
970   }
971 }
972 
973 std::unique_ptr<TargetDataLowering>
createLowering(GlobalContext * Ctx)974 TargetDataLowering::createLowering(GlobalContext *Ctx) {
975   TargetArch Target = getFlags().getTargetArch();
976   switch (Target) {
977   default:
978     badTargetFatalError(Target);
979 #define SUBZERO_TARGET(X)                                                      \
980   case TARGET_LOWERING_CLASS_FOR(X):                                           \
981     return ::X::createTargetDataLowering(Ctx);
982 #include "SZTargets.def"
983 #undef SUBZERO_TARGET
984   }
985 }
986 
987 TargetDataLowering::~TargetDataLowering() = default;
988 
989 namespace {
990 
991 // dataSectionSuffix decides whether to use SectionSuffix or VarName as data
992 // section suffix. Essentially, when using separate data sections for globals
993 // SectionSuffix is not necessary.
dataSectionSuffix(const std::string & SectionSuffix,const std::string & VarName,const bool DataSections)994 std::string dataSectionSuffix(const std::string &SectionSuffix,
995                               const std::string &VarName,
996                               const bool DataSections) {
997   if (SectionSuffix.empty() && !DataSections) {
998     return "";
999   }
1000 
1001   if (DataSections) {
1002     // With data sections we don't need to use the SectionSuffix.
1003     return "." + VarName;
1004   }
1005 
1006   assert(!SectionSuffix.empty());
1007   return "." + SectionSuffix;
1008 }
1009 
1010 } // end of anonymous namespace
1011 
emitGlobal(const VariableDeclaration & Var,const std::string & SectionSuffix)1012 void TargetDataLowering::emitGlobal(const VariableDeclaration &Var,
1013                                     const std::string &SectionSuffix) {
1014   if (!BuildDefs::dump())
1015     return;
1016 
1017   // If external and not initialized, this must be a cross test. Don't generate
1018   // a declaration for such cases.
1019   const bool IsExternal = Var.isExternal() || getFlags().getDisableInternal();
1020   if (IsExternal && !Var.hasInitializer())
1021     return;
1022 
1023   Ostream &Str = Ctx->getStrEmit();
1024   const bool HasNonzeroInitializer = Var.hasNonzeroInitializer();
1025   const bool IsConstant = Var.getIsConstant();
1026   const SizeT Size = Var.getNumBytes();
1027   const std::string Name = Var.getName().toString();
1028 
1029   Str << "\t.type\t" << Name << ",%object\n";
1030 
1031   const bool UseDataSections = getFlags().getDataSections();
1032   const bool UseNonsfi = getFlags().getUseNonsfi();
1033   const std::string Suffix =
1034       dataSectionSuffix(SectionSuffix, Name, UseDataSections);
1035   if (IsConstant && UseNonsfi)
1036     Str << "\t.section\t.data.rel.ro" << Suffix << ",\"aw\",%progbits\n";
1037   else if (IsConstant)
1038     Str << "\t.section\t.rodata" << Suffix << ",\"a\",%progbits\n";
1039   else if (HasNonzeroInitializer)
1040     Str << "\t.section\t.data" << Suffix << ",\"aw\",%progbits\n";
1041   else
1042     Str << "\t.section\t.bss" << Suffix << ",\"aw\",%nobits\n";
1043 
1044   if (IsExternal)
1045     Str << "\t.globl\t" << Name << "\n";
1046 
1047   const uint32_t Align = Var.getAlignment();
1048   if (Align > 1) {
1049     assert(llvm::isPowerOf2_32(Align));
1050     // Use the .p2align directive, since the .align N directive can either
1051     // interpret N as bytes, or power of 2 bytes, depending on the target.
1052     Str << "\t.p2align\t" << llvm::Log2_32(Align) << "\n";
1053   }
1054 
1055   Str << Name << ":\n";
1056 
1057   if (HasNonzeroInitializer) {
1058     for (const auto *Init : Var.getInitializers()) {
1059       switch (Init->getKind()) {
1060       case VariableDeclaration::Initializer::DataInitializerKind: {
1061         const auto &Data =
1062             llvm::cast<VariableDeclaration::DataInitializer>(Init)
1063                 ->getContents();
1064         for (SizeT i = 0; i < Init->getNumBytes(); ++i) {
1065           Str << "\t.byte\t" << (((unsigned)Data[i]) & 0xff) << "\n";
1066         }
1067         break;
1068       }
1069       case VariableDeclaration::Initializer::ZeroInitializerKind:
1070         Str << "\t.zero\t" << Init->getNumBytes() << "\n";
1071         break;
1072       case VariableDeclaration::Initializer::RelocInitializerKind: {
1073         const auto *Reloc =
1074             llvm::cast<VariableDeclaration::RelocInitializer>(Init);
1075         Str << "\t" << getEmit32Directive() << "\t";
1076         Str << Reloc->getDeclaration()->getName();
1077         if (Reloc->hasFixup()) {
1078           // TODO(jpp): this is ARM32 specific.
1079           Str << "(GOTOFF)";
1080         }
1081         if (RelocOffsetT Offset = Reloc->getOffset()) {
1082           if (Offset >= 0 || (Offset == INT32_MIN))
1083             Str << " + " << Offset;
1084           else
1085             Str << " - " << -Offset;
1086         }
1087         Str << "\n";
1088         break;
1089       }
1090       }
1091     }
1092   } else {
1093     // NOTE: for non-constant zero initializers, this is BSS (no bits), so an
1094     // ELF writer would not write to the file, and only track virtual offsets,
1095     // but the .s writer still needs this .zero and cannot simply use the .size
1096     // to advance offsets.
1097     Str << "\t.zero\t" << Size << "\n";
1098   }
1099 
1100   Str << "\t.size\t" << Name << ", " << Size << "\n";
1101 }
1102 
1103 std::unique_ptr<TargetHeaderLowering>
createLowering(GlobalContext * Ctx)1104 TargetHeaderLowering::createLowering(GlobalContext *Ctx) {
1105   TargetArch Target = getFlags().getTargetArch();
1106   switch (Target) {
1107   default:
1108     badTargetFatalError(Target);
1109 #define SUBZERO_TARGET(X)                                                      \
1110   case TARGET_LOWERING_CLASS_FOR(X):                                           \
1111     return ::X::createTargetHeaderLowering(Ctx);
1112 #include "SZTargets.def"
1113 #undef SUBZERO_TARGET
1114   }
1115 }
1116 
1117 TargetHeaderLowering::~TargetHeaderLowering() = default;
1118 
1119 } // end of namespace Ice
1120