1 //===-- Analysis.cpp - CodeGen LLVM IR Analysis Utilities -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines several CodeGen-specific LLVM IR analysis utilties.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/CodeGen/Analysis.h"
15 #include "llvm/Analysis/ValueTracking.h"
16 #include "llvm/CodeGen/MachineFunction.h"
17 #include "llvm/IR/DataLayout.h"
18 #include "llvm/IR/DerivedTypes.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/IR/Instructions.h"
21 #include "llvm/IR/IntrinsicInst.h"
22 #include "llvm/IR/LLVMContext.h"
23 #include "llvm/IR/Module.h"
24 #include "llvm/Support/ErrorHandling.h"
25 #include "llvm/Support/MathExtras.h"
26 #include "llvm/Target/TargetLowering.h"
29 /// ComputeLinearIndex - Given an LLVM IR aggregate type and a sequence
30 /// of insertvalue or extractvalue indices that identify a member, return
31 /// the linearized index of the start of the member.
33 unsigned llvm::ComputeLinearIndex(Type *Ty,
34 const unsigned *Indices,
35 const unsigned *IndicesEnd,
37 // Base case: We're done.
38 if (Indices && Indices == IndicesEnd)
41 // Given a struct type, recursively traverse the elements.
42 if (StructType *STy = dyn_cast<StructType>(Ty)) {
43 for (StructType::element_iterator EB = STy->element_begin(),
45 EE = STy->element_end();
47 if (Indices && *Indices == unsigned(EI - EB))
48 return ComputeLinearIndex(*EI, Indices+1, IndicesEnd, CurIndex);
49 CurIndex = ComputeLinearIndex(*EI, 0, 0, CurIndex);
53 // Given an array type, recursively traverse the elements.
54 else if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
55 Type *EltTy = ATy->getElementType();
56 for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i) {
57 if (Indices && *Indices == i)
58 return ComputeLinearIndex(EltTy, Indices+1, IndicesEnd, CurIndex);
59 CurIndex = ComputeLinearIndex(EltTy, 0, 0, CurIndex);
63 // We haven't found the type we're looking for, so keep searching.
67 /// ComputeValueVTs - Given an LLVM IR type, compute a sequence of
68 /// EVTs that represent all the individual underlying
69 /// non-aggregate types that comprise it.
71 /// If Offsets is non-null, it points to a vector to be filled in
72 /// with the in-memory offsets of each of the individual values.
74 void llvm::ComputeValueVTs(const TargetLowering &TLI, Type *Ty,
75 SmallVectorImpl<EVT> &ValueVTs,
76 SmallVectorImpl<uint64_t> *Offsets,
77 uint64_t StartingOffset) {
78 // Given a struct type, recursively traverse the elements.
79 if (StructType *STy = dyn_cast<StructType>(Ty)) {
80 const StructLayout *SL = TLI.getDataLayout()->getStructLayout(STy);
81 for (StructType::element_iterator EB = STy->element_begin(),
83 EE = STy->element_end();
85 ComputeValueVTs(TLI, *EI, ValueVTs, Offsets,
86 StartingOffset + SL->getElementOffset(EI - EB));
89 // Given an array type, recursively traverse the elements.
90 if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
91 Type *EltTy = ATy->getElementType();
92 uint64_t EltSize = TLI.getDataLayout()->getTypeAllocSize(EltTy);
93 for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i)
94 ComputeValueVTs(TLI, EltTy, ValueVTs, Offsets,
95 StartingOffset + i * EltSize);
98 // Interpret void as zero return values.
101 // Base case: we can get an EVT for this LLVM IR type.
102 ValueVTs.push_back(TLI.getValueType(Ty));
104 Offsets->push_back(StartingOffset);
107 /// ExtractTypeInfo - Returns the type info, possibly bitcast, encoded in V.
108 GlobalVariable *llvm::ExtractTypeInfo(Value *V) {
109 V = V->stripPointerCasts();
110 GlobalVariable *GV = dyn_cast<GlobalVariable>(V);
112 if (GV && GV->getName() == "llvm.eh.catch.all.value") {
113 assert(GV->hasInitializer() &&
114 "The EH catch-all value must have an initializer");
115 Value *Init = GV->getInitializer();
116 GV = dyn_cast<GlobalVariable>(Init);
117 if (!GV) V = cast<ConstantPointerNull>(Init);
120 assert((GV || isa<ConstantPointerNull>(V)) &&
121 "TypeInfo must be a global variable or NULL");
125 /// hasInlineAsmMemConstraint - Return true if the inline asm instruction being
126 /// processed uses a memory 'm' constraint.
128 llvm::hasInlineAsmMemConstraint(InlineAsm::ConstraintInfoVector &CInfos,
129 const TargetLowering &TLI) {
130 for (unsigned i = 0, e = CInfos.size(); i != e; ++i) {
131 InlineAsm::ConstraintInfo &CI = CInfos[i];
132 for (unsigned j = 0, ee = CI.Codes.size(); j != ee; ++j) {
133 TargetLowering::ConstraintType CType = TLI.getConstraintType(CI.Codes[j]);
134 if (CType == TargetLowering::C_Memory)
138 // Indirect operand accesses access memory.
146 /// getFCmpCondCode - Return the ISD condition code corresponding to
147 /// the given LLVM IR floating-point condition code. This includes
148 /// consideration of global floating-point math flags.
150 ISD::CondCode llvm::getFCmpCondCode(FCmpInst::Predicate Pred) {
152 case FCmpInst::FCMP_FALSE: return ISD::SETFALSE;
153 case FCmpInst::FCMP_OEQ: return ISD::SETOEQ;
154 case FCmpInst::FCMP_OGT: return ISD::SETOGT;
155 case FCmpInst::FCMP_OGE: return ISD::SETOGE;
156 case FCmpInst::FCMP_OLT: return ISD::SETOLT;
157 case FCmpInst::FCMP_OLE: return ISD::SETOLE;
158 case FCmpInst::FCMP_ONE: return ISD::SETONE;
159 case FCmpInst::FCMP_ORD: return ISD::SETO;
160 case FCmpInst::FCMP_UNO: return ISD::SETUO;
161 case FCmpInst::FCMP_UEQ: return ISD::SETUEQ;
162 case FCmpInst::FCMP_UGT: return ISD::SETUGT;
163 case FCmpInst::FCMP_UGE: return ISD::SETUGE;
164 case FCmpInst::FCMP_ULT: return ISD::SETULT;
165 case FCmpInst::FCMP_ULE: return ISD::SETULE;
166 case FCmpInst::FCMP_UNE: return ISD::SETUNE;
167 case FCmpInst::FCMP_TRUE: return ISD::SETTRUE;
168 default: llvm_unreachable("Invalid FCmp predicate opcode!");
172 ISD::CondCode llvm::getFCmpCodeWithoutNaN(ISD::CondCode CC) {
174 case ISD::SETOEQ: case ISD::SETUEQ: return ISD::SETEQ;
175 case ISD::SETONE: case ISD::SETUNE: return ISD::SETNE;
176 case ISD::SETOLT: case ISD::SETULT: return ISD::SETLT;
177 case ISD::SETOLE: case ISD::SETULE: return ISD::SETLE;
178 case ISD::SETOGT: case ISD::SETUGT: return ISD::SETGT;
179 case ISD::SETOGE: case ISD::SETUGE: return ISD::SETGE;
184 /// getICmpCondCode - Return the ISD condition code corresponding to
185 /// the given LLVM IR integer condition code.
187 ISD::CondCode llvm::getICmpCondCode(ICmpInst::Predicate Pred) {
189 case ICmpInst::ICMP_EQ: return ISD::SETEQ;
190 case ICmpInst::ICMP_NE: return ISD::SETNE;
191 case ICmpInst::ICMP_SLE: return ISD::SETLE;
192 case ICmpInst::ICMP_ULE: return ISD::SETULE;
193 case ICmpInst::ICMP_SGE: return ISD::SETGE;
194 case ICmpInst::ICMP_UGE: return ISD::SETUGE;
195 case ICmpInst::ICMP_SLT: return ISD::SETLT;
196 case ICmpInst::ICMP_ULT: return ISD::SETULT;
197 case ICmpInst::ICMP_SGT: return ISD::SETGT;
198 case ICmpInst::ICMP_UGT: return ISD::SETUGT;
200 llvm_unreachable("Invalid ICmp predicate opcode!");
204 static bool isNoopBitcast(Type *T1, Type *T2,
205 const TargetLoweringBase& TLI) {
206 return T1 == T2 || (T1->isPointerTy() && T2->isPointerTy()) ||
207 (isa<VectorType>(T1) && isa<VectorType>(T2) &&
208 TLI.isTypeLegal(EVT::getEVT(T1)) && TLI.isTypeLegal(EVT::getEVT(T2)));
211 /// Look through operations that will be free to find the earliest source of
214 /// @param ValLoc If V has aggegate type, we will be interested in a particular
215 /// scalar component. This records its address; the reverse of this list gives a
216 /// sequence of indices appropriate for an extractvalue to locate the important
217 /// value. This value is updated during the function and on exit will indicate
218 /// similar information for the Value returned.
220 /// @param DataBits If this function looks through truncate instructions, this
221 /// will record the smallest size attained.
222 static const Value *getNoopInput(const Value *V,
223 SmallVectorImpl<unsigned> &ValLoc,
225 const TargetLoweringBase &TLI) {
227 // Try to look through V1; if V1 is not an instruction, it can't be looked
229 const Instruction *I = dyn_cast<Instruction>(V);
230 if (!I || I->getNumOperands() == 0) return V;
231 const Value *NoopInput = 0;
233 Value *Op = I->getOperand(0);
234 if (isa<BitCastInst>(I)) {
235 // Look through truly no-op bitcasts.
236 if (isNoopBitcast(Op->getType(), I->getType(), TLI))
238 } else if (isa<GetElementPtrInst>(I)) {
239 // Look through getelementptr
240 if (cast<GetElementPtrInst>(I)->hasAllZeroIndices())
242 } else if (isa<IntToPtrInst>(I)) {
243 // Look through inttoptr.
244 // Make sure this isn't a truncating or extending cast. We could
245 // support this eventually, but don't bother for now.
246 if (!isa<VectorType>(I->getType()) &&
247 TLI.getPointerTy().getSizeInBits() ==
248 cast<IntegerType>(Op->getType())->getBitWidth())
250 } else if (isa<PtrToIntInst>(I)) {
251 // Look through ptrtoint.
252 // Make sure this isn't a truncating or extending cast. We could
253 // support this eventually, but don't bother for now.
254 if (!isa<VectorType>(I->getType()) &&
255 TLI.getPointerTy().getSizeInBits() ==
256 cast<IntegerType>(I->getType())->getBitWidth())
258 } else if (isa<TruncInst>(I) &&
259 TLI.allowTruncateForTailCall(Op->getType(), I->getType())) {
260 DataBits = std::min(DataBits, I->getType()->getPrimitiveSizeInBits());
262 } else if (isa<CallInst>(I)) {
263 // Look through call (skipping callee)
264 for (User::const_op_iterator i = I->op_begin(), e = I->op_end() - 1;
266 unsigned attrInd = i - I->op_begin() + 1;
267 if (cast<CallInst>(I)->paramHasAttr(attrInd, Attribute::Returned) &&
268 isNoopBitcast((*i)->getType(), I->getType(), TLI)) {
273 } else if (isa<InvokeInst>(I)) {
274 // Look through invoke (skipping BB, BB, Callee)
275 for (User::const_op_iterator i = I->op_begin(), e = I->op_end() - 3;
277 unsigned attrInd = i - I->op_begin() + 1;
278 if (cast<InvokeInst>(I)->paramHasAttr(attrInd, Attribute::Returned) &&
279 isNoopBitcast((*i)->getType(), I->getType(), TLI)) {
284 } else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(V)) {
285 // Value may come from either the aggregate or the scalar
286 ArrayRef<unsigned> InsertLoc = IVI->getIndices();
287 if (std::equal(InsertLoc.rbegin(), InsertLoc.rend(),
289 // The type being inserted is a nested sub-type of the aggregate; we
290 // have to remove those initial indices to get the location we're
291 // interested in for the operand.
292 ValLoc.resize(ValLoc.size() - InsertLoc.size());
293 NoopInput = IVI->getInsertedValueOperand();
295 // The struct we're inserting into has the value we're interested in, no
296 // change of address.
299 } else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(V)) {
300 // The part we're interested in will inevitably be some sub-section of the
301 // previous aggregate. Combine the two paths to obtain the true address of
303 ArrayRef<unsigned> ExtractLoc = EVI->getIndices();
304 std::copy(ExtractLoc.rbegin(), ExtractLoc.rend(),
305 std::back_inserter(ValLoc));
308 // Terminate if we couldn't find anything to look through.
316 /// Return true if this scalar return value only has bits discarded on its path
317 /// from the "tail call" to the "ret". This includes the obvious noop
318 /// instructions handled by getNoopInput above as well as free truncations (or
319 /// extensions prior to the call).
320 static bool slotOnlyDiscardsData(const Value *RetVal, const Value *CallVal,
321 SmallVectorImpl<unsigned> &RetIndices,
322 SmallVectorImpl<unsigned> &CallIndices,
323 bool AllowDifferingSizes,
324 const TargetLoweringBase &TLI) {
326 // Trace the sub-value needed by the return value as far back up the graph as
327 // possible, in the hope that it will intersect with the value produced by the
328 // call. In the simple case with no "returned" attribute, the hope is actually
329 // that we end up back at the tail call instruction itself.
330 unsigned BitsRequired = UINT_MAX;
331 RetVal = getNoopInput(RetVal, RetIndices, BitsRequired, TLI);
333 // If this slot in the value returned is undef, it doesn't matter what the
334 // call puts there, it'll be fine.
335 if (isa<UndefValue>(RetVal))
338 // Now do a similar search up through the graph to find where the value
339 // actually returned by the "tail call" comes from. In the simple case without
340 // a "returned" attribute, the search will be blocked immediately and the loop
342 unsigned BitsProvided = UINT_MAX;
343 CallVal = getNoopInput(CallVal, CallIndices, BitsProvided, TLI);
345 // There's no hope if we can't actually trace them to (the same part of!) the
347 if (CallVal != RetVal || CallIndices != RetIndices)
350 // However, intervening truncates may have made the call non-tail. Make sure
351 // all the bits that are needed by the "ret" have been provided by the "tail
352 // call". FIXME: with sufficiently cunning bit-tracking, we could look through
354 if (BitsProvided < BitsRequired ||
355 (!AllowDifferingSizes && BitsProvided != BitsRequired))
361 /// For an aggregate type, determine whether a given index is within bounds or
363 static bool indexReallyValid(CompositeType *T, unsigned Idx) {
364 if (ArrayType *AT = dyn_cast<ArrayType>(T))
365 return Idx < AT->getNumElements();
367 return Idx < cast<StructType>(T)->getNumElements();
370 /// Move the given iterators to the next leaf type in depth first traversal.
372 /// Performs a depth-first traversal of the type as specified by its arguments,
373 /// stopping at the next leaf node (which may be a legitimate scalar type or an
374 /// empty struct or array).
376 /// @param SubTypes List of the partial components making up the type from
377 /// outermost to innermost non-empty aggregate. The element currently
378 /// represented is SubTypes.back()->getTypeAtIndex(Path.back() - 1).
380 /// @param Path Set of extractvalue indices leading from the outermost type
381 /// (SubTypes[0]) to the leaf node currently represented.
383 /// @returns true if a new type was found, false otherwise. Calling this
384 /// function again on a finished iterator will repeatedly return
385 /// false. SubTypes.back()->getTypeAtIndex(Path.back()) is either an empty
386 /// aggregate or a non-aggregate
387 static bool advanceToNextLeafType(SmallVectorImpl<CompositeType *> &SubTypes,
388 SmallVectorImpl<unsigned> &Path) {
389 // First march back up the tree until we can successfully increment one of the
390 // coordinates in Path.
391 while (!Path.empty() && !indexReallyValid(SubTypes.back(), Path.back() + 1)) {
396 // If we reached the top, then the iterator is done.
400 // We know there's *some* valid leaf now, so march back down the tree picking
401 // out the left-most element at each node.
403 Type *DeeperType = SubTypes.back()->getTypeAtIndex(Path.back());
404 while (DeeperType->isAggregateType()) {
405 CompositeType *CT = cast<CompositeType>(DeeperType);
406 if (!indexReallyValid(CT, 0))
409 SubTypes.push_back(CT);
412 DeeperType = CT->getTypeAtIndex(0U);
418 /// Find the first non-empty, scalar-like type in Next and setup the iterator
421 /// Assuming Next is an aggregate of some kind, this function will traverse the
422 /// tree from left to right (i.e. depth-first) looking for the first
423 /// non-aggregate type which will play a role in function return.
425 /// For example, if Next was {[0 x i64], {{}, i32, {}}, i32} then we would setup
426 /// Path as [1, 1] and SubTypes as [Next, {{}, i32, {}}] to represent the first
427 /// i32 in that type.
428 static bool firstRealType(Type *Next,
429 SmallVectorImpl<CompositeType *> &SubTypes,
430 SmallVectorImpl<unsigned> &Path) {
431 // First initialise the iterator components to the first "leaf" node
432 // (i.e. node with no valid sub-type at any index, so {} does count as a leaf
433 // despite nominally being an aggregate).
434 while (Next->isAggregateType() &&
435 indexReallyValid(cast<CompositeType>(Next), 0)) {
436 SubTypes.push_back(cast<CompositeType>(Next));
438 Next = cast<CompositeType>(Next)->getTypeAtIndex(0U);
441 // If there's no Path now, Next was originally scalar already (or empty
442 // leaf). We're done.
446 // Otherwise, use normal iteration to keep looking through the tree until we
447 // find a non-aggregate type.
448 while (SubTypes.back()->getTypeAtIndex(Path.back())->isAggregateType()) {
449 if (!advanceToNextLeafType(SubTypes, Path))
456 /// Set the iterator data-structures to the next non-empty, non-aggregate
458 static bool nextRealType(SmallVectorImpl<CompositeType *> &SubTypes,
459 SmallVectorImpl<unsigned> &Path) {
461 if (!advanceToNextLeafType(SubTypes, Path))
464 assert(!Path.empty() && "found a leaf but didn't set the path?");
465 } while (SubTypes.back()->getTypeAtIndex(Path.back())->isAggregateType());
471 /// Test if the given instruction is in a position to be optimized
472 /// with a tail-call. This roughly means that it's in a block with
473 /// a return and there's nothing that needs to be scheduled
474 /// between it and the return.
476 /// This function only tests target-independent requirements.
477 bool llvm::isInTailCallPosition(ImmutableCallSite CS,
478 const TargetLowering &TLI) {
479 const Instruction *I = CS.getInstruction();
480 const BasicBlock *ExitBB = I->getParent();
481 const TerminatorInst *Term = ExitBB->getTerminator();
482 const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
484 // The block must end in a return statement or unreachable.
486 // FIXME: Decline tailcall if it's not guaranteed and if the block ends in
487 // an unreachable, for now. The way tailcall optimization is currently
488 // implemented means it will add an epilogue followed by a jump. That is
489 // not profitable. Also, if the callee is a special function (e.g.
490 // longjmp on x86), it can end up causing miscompilation that has not
491 // been fully understood.
493 (!TLI.getTargetMachine().Options.GuaranteedTailCallOpt ||
494 !isa<UnreachableInst>(Term)))
497 // If I will have a chain, make sure no other instruction that will have a
498 // chain interposes between I and the return.
499 if (I->mayHaveSideEffects() || I->mayReadFromMemory() ||
500 !isSafeToSpeculativelyExecute(I))
501 for (BasicBlock::const_iterator BBI = prior(prior(ExitBB->end())); ;
505 // Debug info intrinsics do not get in the way of tail call optimization.
506 if (isa<DbgInfoIntrinsic>(BBI))
508 if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
509 !isSafeToSpeculativelyExecute(BBI))
513 // If the block ends with a void return or unreachable, it doesn't matter
514 // what the call's return type is.
515 if (!Ret || Ret->getNumOperands() == 0) return true;
517 // If the return value is undef, it doesn't matter what the call's
519 if (isa<UndefValue>(Ret->getOperand(0))) return true;
521 // Make sure the attributes attached to each return are compatible.
522 AttrBuilder CallerAttrs(ExitBB->getParent()->getAttributes(),
523 AttributeSet::ReturnIndex);
524 AttrBuilder CalleeAttrs(cast<CallInst>(I)->getAttributes(),
525 AttributeSet::ReturnIndex);
527 // Noalias is completely benign as far as calling convention goes, it
528 // shouldn't affect whether the call is a tail call.
529 CallerAttrs = CallerAttrs.removeAttribute(Attribute::NoAlias);
530 CalleeAttrs = CalleeAttrs.removeAttribute(Attribute::NoAlias);
532 bool AllowDifferingSizes = true;
533 if (CallerAttrs.contains(Attribute::ZExt)) {
534 if (!CalleeAttrs.contains(Attribute::ZExt))
537 AllowDifferingSizes = false;
538 CallerAttrs.removeAttribute(Attribute::ZExt);
539 CalleeAttrs.removeAttribute(Attribute::ZExt);
540 } else if (CallerAttrs.contains(Attribute::SExt)) {
541 if (!CalleeAttrs.contains(Attribute::SExt))
544 AllowDifferingSizes = false;
545 CallerAttrs.removeAttribute(Attribute::SExt);
546 CalleeAttrs.removeAttribute(Attribute::SExt);
549 // If they're still different, there's some facet we don't understand
550 // (currently only "inreg", but in future who knows). It may be OK but the
551 // only safe option is to reject the tail call.
552 if (CallerAttrs != CalleeAttrs)
555 const Value *RetVal = Ret->getOperand(0), *CallVal = I;
556 SmallVector<unsigned, 4> RetPath, CallPath;
557 SmallVector<CompositeType *, 4> RetSubTypes, CallSubTypes;
559 bool RetEmpty = !firstRealType(RetVal->getType(), RetSubTypes, RetPath);
560 bool CallEmpty = !firstRealType(CallVal->getType(), CallSubTypes, CallPath);
562 // Nothing's actually returned, it doesn't matter what the callee put there
563 // it's a valid tail call.
567 // Iterate pairwise through each of the value types making up the tail call
568 // and the corresponding return. For each one we want to know whether it's
569 // essentially going directly from the tail call to the ret, via operations
570 // that end up not generating any code.
572 // We allow a certain amount of covariance here. For example it's permitted
573 // for the tail call to define more bits than the ret actually cares about
574 // (e.g. via a truncate).
577 // We've exhausted the values produced by the tail call instruction, the
578 // rest are essentially undef. The type doesn't really matter, but we need
580 Type *SlotType = RetSubTypes.back()->getTypeAtIndex(RetPath.back());
581 CallVal = UndefValue::get(SlotType);
584 // The manipulations performed when we're looking through an insertvalue or
585 // an extractvalue would happen at the front of the RetPath list, so since
586 // we have to copy it anyway it's more efficient to create a reversed copy.
588 SmallVector<unsigned, 4> TmpRetPath, TmpCallPath;
589 copy(RetPath.rbegin(), RetPath.rend(), std::back_inserter(TmpRetPath));
590 copy(CallPath.rbegin(), CallPath.rend(), std::back_inserter(TmpCallPath));
592 // Finally, we can check whether the value produced by the tail call at this
593 // index is compatible with the value we return.
594 if (!slotOnlyDiscardsData(RetVal, CallVal, TmpRetPath, TmpCallPath,
595 AllowDifferingSizes, TLI))
598 CallEmpty = !nextRealType(CallSubTypes, CallPath);
599 } while(nextRealType(RetSubTypes, RetPath));