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llvm-mirror/lib/CodeGen/Analysis.cpp
Michael Gottesman d2ede9d0a0 [stackprotector] Refactor out the end of isInTailCallPosition into the function returnTypeIsEligibleForTailCall. 
This allows me to use returnTypeIsEligibleForTailCall in the stack protector pass.

rdar://13935163

llvm-svn: 188765
2013-08-20 08:36:50 +00:00

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//===-- Analysis.cpp - CodeGen LLVM IR Analysis Utilities -----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines several CodeGen-specific LLVM IR analysis utilties.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Analysis.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Target/TargetLowering.h"
using namespace llvm;
/// ComputeLinearIndex - Given an LLVM IR aggregate type and a sequence
/// of insertvalue or extractvalue indices that identify a member, return
/// the linearized index of the start of the member.
///
unsigned llvm::ComputeLinearIndex(Type *Ty,
const unsigned *Indices,
const unsigned *IndicesEnd,
unsigned CurIndex) {
// Base case: We're done.
if (Indices && Indices == IndicesEnd)
return CurIndex;
// Given a struct type, recursively traverse the elements.
if (StructType *STy = dyn_cast<StructType>(Ty)) {
for (StructType::element_iterator EB = STy->element_begin(),
EI = EB,
EE = STy->element_end();
EI != EE; ++EI) {
if (Indices && *Indices == unsigned(EI - EB))
return ComputeLinearIndex(*EI, Indices+1, IndicesEnd, CurIndex);
CurIndex = ComputeLinearIndex(*EI, 0, 0, CurIndex);
}
return CurIndex;
}
// Given an array type, recursively traverse the elements.
else if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
Type *EltTy = ATy->getElementType();
for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i) {
if (Indices && *Indices == i)
return ComputeLinearIndex(EltTy, Indices+1, IndicesEnd, CurIndex);
CurIndex = ComputeLinearIndex(EltTy, 0, 0, CurIndex);
}
return CurIndex;
}
// We haven't found the type we're looking for, so keep searching.
return CurIndex + 1;
}
/// ComputeValueVTs - Given an LLVM IR type, compute a sequence of
/// EVTs that represent all the individual underlying
/// non-aggregate types that comprise it.
///
/// If Offsets is non-null, it points to a vector to be filled in
/// with the in-memory offsets of each of the individual values.
///
void llvm::ComputeValueVTs(const TargetLowering &TLI, Type *Ty,
SmallVectorImpl<EVT> &ValueVTs,
SmallVectorImpl<uint64_t> *Offsets,
uint64_t StartingOffset) {
// Given a struct type, recursively traverse the elements.
if (StructType *STy = dyn_cast<StructType>(Ty)) {
const StructLayout *SL = TLI.getDataLayout()->getStructLayout(STy);
for (StructType::element_iterator EB = STy->element_begin(),
EI = EB,
EE = STy->element_end();
EI != EE; ++EI)
ComputeValueVTs(TLI, *EI, ValueVTs, Offsets,
StartingOffset + SL->getElementOffset(EI - EB));
return;
}
// Given an array type, recursively traverse the elements.
if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
Type *EltTy = ATy->getElementType();
uint64_t EltSize = TLI.getDataLayout()->getTypeAllocSize(EltTy);
for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i)
ComputeValueVTs(TLI, EltTy, ValueVTs, Offsets,
StartingOffset + i * EltSize);
return;
}
// Interpret void as zero return values.
if (Ty->isVoidTy())
return;
// Base case: we can get an EVT for this LLVM IR type.
ValueVTs.push_back(TLI.getValueType(Ty));
if (Offsets)
Offsets->push_back(StartingOffset);
}
/// ExtractTypeInfo - Returns the type info, possibly bitcast, encoded in V.
GlobalVariable *llvm::ExtractTypeInfo(Value *V) {
V = V->stripPointerCasts();
GlobalVariable *GV = dyn_cast<GlobalVariable>(V);
if (GV && GV->getName() == "llvm.eh.catch.all.value") {
assert(GV->hasInitializer() &&
"The EH catch-all value must have an initializer");
Value *Init = GV->getInitializer();
GV = dyn_cast<GlobalVariable>(Init);
if (!GV) V = cast<ConstantPointerNull>(Init);
}
assert((GV || isa<ConstantPointerNull>(V)) &&
"TypeInfo must be a global variable or NULL");
return GV;
}
/// hasInlineAsmMemConstraint - Return true if the inline asm instruction being
/// processed uses a memory 'm' constraint.
bool
llvm::hasInlineAsmMemConstraint(InlineAsm::ConstraintInfoVector &CInfos,
const TargetLowering &TLI) {
for (unsigned i = 0, e = CInfos.size(); i != e; ++i) {
InlineAsm::ConstraintInfo &CI = CInfos[i];
for (unsigned j = 0, ee = CI.Codes.size(); j != ee; ++j) {
TargetLowering::ConstraintType CType = TLI.getConstraintType(CI.Codes[j]);
if (CType == TargetLowering::C_Memory)
return true;
}
// Indirect operand accesses access memory.
if (CI.isIndirect)
return true;
}
return false;
}
/// getFCmpCondCode - Return the ISD condition code corresponding to
/// the given LLVM IR floating-point condition code. This includes
/// consideration of global floating-point math flags.
///
ISD::CondCode llvm::getFCmpCondCode(FCmpInst::Predicate Pred) {
switch (Pred) {
case FCmpInst::FCMP_FALSE: return ISD::SETFALSE;
case FCmpInst::FCMP_OEQ: return ISD::SETOEQ;
case FCmpInst::FCMP_OGT: return ISD::SETOGT;
case FCmpInst::FCMP_OGE: return ISD::SETOGE;
case FCmpInst::FCMP_OLT: return ISD::SETOLT;
case FCmpInst::FCMP_OLE: return ISD::SETOLE;
case FCmpInst::FCMP_ONE: return ISD::SETONE;
case FCmpInst::FCMP_ORD: return ISD::SETO;
case FCmpInst::FCMP_UNO: return ISD::SETUO;
case FCmpInst::FCMP_UEQ: return ISD::SETUEQ;
case FCmpInst::FCMP_UGT: return ISD::SETUGT;
case FCmpInst::FCMP_UGE: return ISD::SETUGE;
case FCmpInst::FCMP_ULT: return ISD::SETULT;
case FCmpInst::FCMP_ULE: return ISD::SETULE;
case FCmpInst::FCMP_UNE: return ISD::SETUNE;
case FCmpInst::FCMP_TRUE: return ISD::SETTRUE;
default: llvm_unreachable("Invalid FCmp predicate opcode!");
}
}
ISD::CondCode llvm::getFCmpCodeWithoutNaN(ISD::CondCode CC) {
switch (CC) {
case ISD::SETOEQ: case ISD::SETUEQ: return ISD::SETEQ;
case ISD::SETONE: case ISD::SETUNE: return ISD::SETNE;
case ISD::SETOLT: case ISD::SETULT: return ISD::SETLT;
case ISD::SETOLE: case ISD::SETULE: return ISD::SETLE;
case ISD::SETOGT: case ISD::SETUGT: return ISD::SETGT;
case ISD::SETOGE: case ISD::SETUGE: return ISD::SETGE;
default: return CC;
}
}
/// getICmpCondCode - Return the ISD condition code corresponding to
/// the given LLVM IR integer condition code.
///
ISD::CondCode llvm::getICmpCondCode(ICmpInst::Predicate Pred) {
switch (Pred) {
case ICmpInst::ICMP_EQ: return ISD::SETEQ;
case ICmpInst::ICMP_NE: return ISD::SETNE;
case ICmpInst::ICMP_SLE: return ISD::SETLE;
case ICmpInst::ICMP_ULE: return ISD::SETULE;
case ICmpInst::ICMP_SGE: return ISD::SETGE;
case ICmpInst::ICMP_UGE: return ISD::SETUGE;
case ICmpInst::ICMP_SLT: return ISD::SETLT;
case ICmpInst::ICMP_ULT: return ISD::SETULT;
case ICmpInst::ICMP_SGT: return ISD::SETGT;
case ICmpInst::ICMP_UGT: return ISD::SETUGT;
default:
llvm_unreachable("Invalid ICmp predicate opcode!");
}
}
static bool isNoopBitcast(Type *T1, Type *T2,
const TargetLoweringBase& TLI) {
return T1 == T2 || (T1->isPointerTy() && T2->isPointerTy()) ||
(isa<VectorType>(T1) && isa<VectorType>(T2) &&
TLI.isTypeLegal(EVT::getEVT(T1)) && TLI.isTypeLegal(EVT::getEVT(T2)));
}
/// Look through operations that will be free to find the earliest source of
/// this value.
///
/// @param ValLoc If V has aggegate type, we will be interested in a particular
/// scalar component. This records its address; the reverse of this list gives a
/// sequence of indices appropriate for an extractvalue to locate the important
/// value. This value is updated during the function and on exit will indicate
/// similar information for the Value returned.
///
/// @param DataBits If this function looks through truncate instructions, this
/// will record the smallest size attained.
static const Value *getNoopInput(const Value *V,
SmallVectorImpl<unsigned> &ValLoc,
unsigned &DataBits,
const TargetLoweringBase &TLI) {
while (true) {
// Try to look through V1; if V1 is not an instruction, it can't be looked
// through.
const Instruction *I = dyn_cast<Instruction>(V);
if (!I || I->getNumOperands() == 0) return V;
const Value *NoopInput = 0;
Value *Op = I->getOperand(0);
if (isa<BitCastInst>(I)) {
// Look through truly no-op bitcasts.
if (isNoopBitcast(Op->getType(), I->getType(), TLI))
NoopInput = Op;
} else if (isa<GetElementPtrInst>(I)) {
// Look through getelementptr
if (cast<GetElementPtrInst>(I)->hasAllZeroIndices())
NoopInput = Op;
} else if (isa<IntToPtrInst>(I)) {
// Look through inttoptr.
// Make sure this isn't a truncating or extending cast. We could
// support this eventually, but don't bother for now.
if (!isa<VectorType>(I->getType()) &&
TLI.getPointerTy().getSizeInBits() ==
cast<IntegerType>(Op->getType())->getBitWidth())
NoopInput = Op;
} else if (isa<PtrToIntInst>(I)) {
// Look through ptrtoint.
// Make sure this isn't a truncating or extending cast. We could
// support this eventually, but don't bother for now.
if (!isa<VectorType>(I->getType()) &&
TLI.getPointerTy().getSizeInBits() ==
cast<IntegerType>(I->getType())->getBitWidth())
NoopInput = Op;
} else if (isa<TruncInst>(I) &&
TLI.allowTruncateForTailCall(Op->getType(), I->getType())) {
DataBits = std::min(DataBits, I->getType()->getPrimitiveSizeInBits());
NoopInput = Op;
} else if (isa<CallInst>(I)) {
// Look through call (skipping callee)
for (User::const_op_iterator i = I->op_begin(), e = I->op_end() - 1;
i != e; ++i) {
unsigned attrInd = i - I->op_begin() + 1;
if (cast<CallInst>(I)->paramHasAttr(attrInd, Attribute::Returned) &&
isNoopBitcast((*i)->getType(), I->getType(), TLI)) {
NoopInput = *i;
break;
}
}
} else if (isa<InvokeInst>(I)) {
// Look through invoke (skipping BB, BB, Callee)
for (User::const_op_iterator i = I->op_begin(), e = I->op_end() - 3;
i != e; ++i) {
unsigned attrInd = i - I->op_begin() + 1;
if (cast<InvokeInst>(I)->paramHasAttr(attrInd, Attribute::Returned) &&
isNoopBitcast((*i)->getType(), I->getType(), TLI)) {
NoopInput = *i;
break;
}
}
} else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(V)) {
// Value may come from either the aggregate or the scalar
ArrayRef<unsigned> InsertLoc = IVI->getIndices();
if (std::equal(InsertLoc.rbegin(), InsertLoc.rend(),
ValLoc.rbegin())) {
// The type being inserted is a nested sub-type of the aggregate; we
// have to remove those initial indices to get the location we're
// interested in for the operand.
ValLoc.resize(ValLoc.size() - InsertLoc.size());
NoopInput = IVI->getInsertedValueOperand();
} else {
// The struct we're inserting into has the value we're interested in, no
// change of address.
NoopInput = Op;
}
} else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(V)) {
// The part we're interested in will inevitably be some sub-section of the
// previous aggregate. Combine the two paths to obtain the true address of
// our element.
ArrayRef<unsigned> ExtractLoc = EVI->getIndices();
std::copy(ExtractLoc.rbegin(), ExtractLoc.rend(),
std::back_inserter(ValLoc));
NoopInput = Op;
}
// Terminate if we couldn't find anything to look through.
if (!NoopInput)
return V;
V = NoopInput;
}
}
/// Return true if this scalar return value only has bits discarded on its path
/// from the "tail call" to the "ret". This includes the obvious noop
/// instructions handled by getNoopInput above as well as free truncations (or
/// extensions prior to the call).
static bool slotOnlyDiscardsData(const Value *RetVal, const Value *CallVal,
SmallVectorImpl<unsigned> &RetIndices,
SmallVectorImpl<unsigned> &CallIndices,
bool AllowDifferingSizes,
const TargetLoweringBase &TLI) {
// Trace the sub-value needed by the return value as far back up the graph as
// possible, in the hope that it will intersect with the value produced by the
// call. In the simple case with no "returned" attribute, the hope is actually
// that we end up back at the tail call instruction itself.
unsigned BitsRequired = UINT_MAX;
RetVal = getNoopInput(RetVal, RetIndices, BitsRequired, TLI);
// If this slot in the value returned is undef, it doesn't matter what the
// call puts there, it'll be fine.
if (isa<UndefValue>(RetVal))
return true;
// Now do a similar search up through the graph to find where the value
// actually returned by the "tail call" comes from. In the simple case without
// a "returned" attribute, the search will be blocked immediately and the loop
// a Noop.
unsigned BitsProvided = UINT_MAX;
CallVal = getNoopInput(CallVal, CallIndices, BitsProvided, TLI);
// There's no hope if we can't actually trace them to (the same part of!) the
// same value.
if (CallVal != RetVal || CallIndices != RetIndices)
return false;
// However, intervening truncates may have made the call non-tail. Make sure
// all the bits that are needed by the "ret" have been provided by the "tail
// call". FIXME: with sufficiently cunning bit-tracking, we could look through
// extensions too.
if (BitsProvided < BitsRequired ||
(!AllowDifferingSizes && BitsProvided != BitsRequired))
return false;
return true;
}
/// For an aggregate type, determine whether a given index is within bounds or
/// not.
static bool indexReallyValid(CompositeType *T, unsigned Idx) {
if (ArrayType *AT = dyn_cast<ArrayType>(T))
return Idx < AT->getNumElements();
return Idx < cast<StructType>(T)->getNumElements();
}
/// Move the given iterators to the next leaf type in depth first traversal.
///
/// Performs a depth-first traversal of the type as specified by its arguments,
/// stopping at the next leaf node (which may be a legitimate scalar type or an
/// empty struct or array).
///
/// @param SubTypes List of the partial components making up the type from
/// outermost to innermost non-empty aggregate. The element currently
/// represented is SubTypes.back()->getTypeAtIndex(Path.back() - 1).
///
/// @param Path Set of extractvalue indices leading from the outermost type
/// (SubTypes[0]) to the leaf node currently represented.
///
/// @returns true if a new type was found, false otherwise. Calling this
/// function again on a finished iterator will repeatedly return
/// false. SubTypes.back()->getTypeAtIndex(Path.back()) is either an empty
/// aggregate or a non-aggregate
static bool advanceToNextLeafType(SmallVectorImpl<CompositeType *> &SubTypes,
SmallVectorImpl<unsigned> &Path) {
// First march back up the tree until we can successfully increment one of the
// coordinates in Path.
while (!Path.empty() && !indexReallyValid(SubTypes.back(), Path.back() + 1)) {
Path.pop_back();
SubTypes.pop_back();
}
// If we reached the top, then the iterator is done.
if (Path.empty())
return false;
// We know there's *some* valid leaf now, so march back down the tree picking
// out the left-most element at each node.
++Path.back();
Type *DeeperType = SubTypes.back()->getTypeAtIndex(Path.back());
while (DeeperType->isAggregateType()) {
CompositeType *CT = cast<CompositeType>(DeeperType);
if (!indexReallyValid(CT, 0))
return true;
SubTypes.push_back(CT);
Path.push_back(0);
DeeperType = CT->getTypeAtIndex(0U);
}
return true;
}
/// Find the first non-empty, scalar-like type in Next and setup the iterator
/// components.
///
/// Assuming Next is an aggregate of some kind, this function will traverse the
/// tree from left to right (i.e. depth-first) looking for the first
/// non-aggregate type which will play a role in function return.
///
/// For example, if Next was {[0 x i64], {{}, i32, {}}, i32} then we would setup
/// Path as [1, 1] and SubTypes as [Next, {{}, i32, {}}] to represent the first
/// i32 in that type.
static bool firstRealType(Type *Next,
SmallVectorImpl<CompositeType *> &SubTypes,
SmallVectorImpl<unsigned> &Path) {
// First initialise the iterator components to the first "leaf" node
// (i.e. node with no valid sub-type at any index, so {} does count as a leaf
// despite nominally being an aggregate).
while (Next->isAggregateType() &&
indexReallyValid(cast<CompositeType>(Next), 0)) {
SubTypes.push_back(cast<CompositeType>(Next));
Path.push_back(0);
Next = cast<CompositeType>(Next)->getTypeAtIndex(0U);
}
// If there's no Path now, Next was originally scalar already (or empty
// leaf). We're done.
if (Path.empty())
return true;
// Otherwise, use normal iteration to keep looking through the tree until we
// find a non-aggregate type.
while (SubTypes.back()->getTypeAtIndex(Path.back())->isAggregateType()) {
if (!advanceToNextLeafType(SubTypes, Path))
return false;
}
return true;
}
/// Set the iterator data-structures to the next non-empty, non-aggregate
/// subtype.
static bool nextRealType(SmallVectorImpl<CompositeType *> &SubTypes,
SmallVectorImpl<unsigned> &Path) {
do {
if (!advanceToNextLeafType(SubTypes, Path))
return false;
assert(!Path.empty() && "found a leaf but didn't set the path?");
} while (SubTypes.back()->getTypeAtIndex(Path.back())->isAggregateType());
return true;
}
/// Test if the given instruction is in a position to be optimized
/// with a tail-call. This roughly means that it's in a block with
/// a return and there's nothing that needs to be scheduled
/// between it and the return.
///
/// This function only tests target-independent requirements.
bool llvm::isInTailCallPosition(ImmutableCallSite CS,
const TargetLowering &TLI) {
const Instruction *I = CS.getInstruction();
const BasicBlock *ExitBB = I->getParent();
const TerminatorInst *Term = ExitBB->getTerminator();
const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
// The block must end in a return statement or unreachable.
//
// FIXME: Decline tailcall if it's not guaranteed and if the block ends in
// an unreachable, for now. The way tailcall optimization is currently
// implemented means it will add an epilogue followed by a jump. That is
// not profitable. Also, if the callee is a special function (e.g.
// longjmp on x86), it can end up causing miscompilation that has not
// been fully understood.
if (!Ret &&
(!TLI.getTargetMachine().Options.GuaranteedTailCallOpt ||
!isa<UnreachableInst>(Term)))
return false;
// If I will have a chain, make sure no other instruction that will have a
// chain interposes between I and the return.
if (I->mayHaveSideEffects() || I->mayReadFromMemory() ||
!isSafeToSpeculativelyExecute(I))
for (BasicBlock::const_iterator BBI = prior(prior(ExitBB->end())); ;
--BBI) {
if (&*BBI == I)
break;
// Debug info intrinsics do not get in the way of tail call optimization.
if (isa<DbgInfoIntrinsic>(BBI))
continue;
if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
!isSafeToSpeculativelyExecute(BBI))
return false;
}
return returnTypeIsEligibleForTailCall(ExitBB->getParent(), I, Ret, TLI);
}
bool llvm::returnTypeIsEligibleForTailCall(const Function *F,
const Instruction *I,
const ReturnInst *Ret,
const TargetLoweringBase &TLI) {
// If the block ends with a void return or unreachable, it doesn't matter
// what the call's return type is.
if (!Ret || Ret->getNumOperands() == 0) return true;
// If the return value is undef, it doesn't matter what the call's
// return type is.
if (isa<UndefValue>(Ret->getOperand(0))) return true;
// Make sure the attributes attached to each return are compatible.
AttrBuilder CallerAttrs(F->getAttributes(),
AttributeSet::ReturnIndex);
AttrBuilder CalleeAttrs(cast<CallInst>(I)->getAttributes(),
AttributeSet::ReturnIndex);
// Noalias is completely benign as far as calling convention goes, it
// shouldn't affect whether the call is a tail call.
CallerAttrs = CallerAttrs.removeAttribute(Attribute::NoAlias);
CalleeAttrs = CalleeAttrs.removeAttribute(Attribute::NoAlias);
bool AllowDifferingSizes = true;
if (CallerAttrs.contains(Attribute::ZExt)) {
if (!CalleeAttrs.contains(Attribute::ZExt))
return false;
AllowDifferingSizes = false;
CallerAttrs.removeAttribute(Attribute::ZExt);
CalleeAttrs.removeAttribute(Attribute::ZExt);
} else if (CallerAttrs.contains(Attribute::SExt)) {
if (!CalleeAttrs.contains(Attribute::SExt))
return false;
AllowDifferingSizes = false;
CallerAttrs.removeAttribute(Attribute::SExt);
CalleeAttrs.removeAttribute(Attribute::SExt);
}
// If they're still different, there's some facet we don't understand
// (currently only "inreg", but in future who knows). It may be OK but the
// only safe option is to reject the tail call.
if (CallerAttrs != CalleeAttrs)
return false;
const Value *RetVal = Ret->getOperand(0), *CallVal = I;
SmallVector<unsigned, 4> RetPath, CallPath;
SmallVector<CompositeType *, 4> RetSubTypes, CallSubTypes;
bool RetEmpty = !firstRealType(RetVal->getType(), RetSubTypes, RetPath);
bool CallEmpty = !firstRealType(CallVal->getType(), CallSubTypes, CallPath);
// Nothing's actually returned, it doesn't matter what the callee put there
// it's a valid tail call.
if (RetEmpty)
return true;
// Iterate pairwise through each of the value types making up the tail call
// and the corresponding return. For each one we want to know whether it's
// essentially going directly from the tail call to the ret, via operations
// that end up not generating any code.
//
// We allow a certain amount of covariance here. For example it's permitted
// for the tail call to define more bits than the ret actually cares about
// (e.g. via a truncate).
do {
if (CallEmpty) {
// We've exhausted the values produced by the tail call instruction, the
// rest are essentially undef. The type doesn't really matter, but we need
// *something*.
Type *SlotType = RetSubTypes.back()->getTypeAtIndex(RetPath.back());
CallVal = UndefValue::get(SlotType);
}
// The manipulations performed when we're looking through an insertvalue or
// an extractvalue would happen at the front of the RetPath list, so since
// we have to copy it anyway it's more efficient to create a reversed copy.
using std::copy;
SmallVector<unsigned, 4> TmpRetPath, TmpCallPath;
copy(RetPath.rbegin(), RetPath.rend(), std::back_inserter(TmpRetPath));
copy(CallPath.rbegin(), CallPath.rend(), std::back_inserter(TmpCallPath));
// Finally, we can check whether the value produced by the tail call at this
// index is compatible with the value we return.
if (!slotOnlyDiscardsData(RetVal, CallVal, TmpRetPath, TmpCallPath,
AllowDifferingSizes, TLI))
return false;
CallEmpty = !nextRealType(CallSubTypes, CallPath);
} while(nextRealType(RetSubTypes, RetPath));
return true;
}
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