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llvm-mirror/lib/CodeGen/Analysis.cpp
Michael Kuperstein 9be926a88e [CGP] Be less conservative about tail-duplicating a ret to allow tail calls 
CGP tail-duplicates rets into blocks that end with a call that feed the ret.
This puts the call in tail position, potentially allowing the DAG builder to
lower it as a tail call. To avoid tail duplication in cases where we won't
form the tail call, CGP tried to predict whether this is going to be possible,
and avoids doing it when lowering as a tail call will definitely fail.
However, it was being too conservative by always throwing away calls to
functions with a signext/zeroext attribute on the return type.

Instead, we can use the same logic the builder uses to determine whether the
attributes work out.

Differential Revision: https://reviews.llvm.org/D24315

llvm-svn: 280894
2016-09-08 00:48:37 +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 utilities.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Analysis.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineModuleInfo.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"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
using namespace llvm;
/// Compute the linearized index of a member in a nested aggregate/struct/array
/// by recursing and accumulating CurIndex as long as there are indices in the
/// index list.
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, nullptr, nullptr, CurIndex);
}
assert(!Indices && "Unexpected out of bound");
return CurIndex;
}
// Given an array type, recursively traverse the elements.
else if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
Type *EltTy = ATy->getElementType();
unsigned NumElts = ATy->getNumElements();
// Compute the Linear offset when jumping one element of the array
unsigned EltLinearOffset = ComputeLinearIndex(EltTy, nullptr, nullptr, 0);
if (Indices) {
assert(*Indices < NumElts && "Unexpected out of bound");
// If the indice is inside the array, compute the index to the requested
// elt and recurse inside the element with the end of the indices list
CurIndex += EltLinearOffset* *Indices;
return ComputeLinearIndex(EltTy, Indices+1, IndicesEnd, CurIndex);
}
CurIndex += EltLinearOffset*NumElts;
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, const DataLayout &DL,
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 = DL.getStructLayout(STy);
for (StructType::element_iterator EB = STy->element_begin(),
EI = EB,
EE = STy->element_end();
EI != EE; ++EI)
ComputeValueVTs(TLI, DL, *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 = DL.getTypeAllocSize(EltTy);
for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i)
ComputeValueVTs(TLI, DL, 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(DL, Ty));
if (Offsets)
Offsets->push_back(StartingOffset);
}
/// ExtractTypeInfo - Returns the type info, possibly bitcast, encoded in V.
GlobalValue *llvm::ExtractTypeInfo(Value *V) {
V = V->stripPointerCasts();
GlobalValue *GV = dyn_cast<GlobalValue>(V);
GlobalVariable *Var = dyn_cast<GlobalVariable>(V);
if (Var && Var->getName() == "llvm.eh.catch.all.value") {
assert(Var->hasInitializer() &&
"The EH catch-all value must have an initializer");
Value *Init = Var->getInitializer();
GV = dyn_cast<GlobalValue>(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,
const DataLayout &DL) {
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 = nullptr;
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()) &&
DL.getPointerSizeInBits() ==
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()) &&
DL.getPointerSizeInBits() ==
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 (ValLoc.size() >= InsertLoc.size() &&
std::equal(InsertLoc.begin(), InsertLoc.end(), 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();
ValLoc.append(ExtractLoc.rbegin(), ExtractLoc.rend());
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,
const DataLayout &DL) {
// 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, DL);
// 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, DL);
// 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 TargetMachine &TM) {
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 &&
(!TM.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 = std::prev(ExitBB->end(), 2);; --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;
}
const Function *F = ExitBB->getParent();
return returnTypeIsEligibleForTailCall(
F, I, Ret, *TM.getSubtargetImpl(*F)->getTargetLowering());
}
bool llvm::attributesPermitTailCall(const Function *F, const Instruction *I,
const ReturnInst *Ret,
const TargetLoweringBase &TLI,
bool *AllowDifferingSizes) {
// ADS may be null, so don't write to it directly.
bool DummyADS;
bool &ADS = AllowDifferingSizes ? *AllowDifferingSizes : DummyADS;
ADS = true;
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);
if (CallerAttrs.contains(Attribute::ZExt)) {
if (!CalleeAttrs.contains(Attribute::ZExt))
return false;
ADS = false;
CallerAttrs.removeAttribute(Attribute::ZExt);
CalleeAttrs.removeAttribute(Attribute::ZExt);
} else if (CallerAttrs.contains(Attribute::SExt)) {
if (!CalleeAttrs.contains(Attribute::SExt))
return false;
ADS = 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.
return CallerAttrs == CalleeAttrs;
}
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.
bool AllowDifferingSizes;
if (!attributesPermitTailCall(F, I, Ret, TLI, &AllowDifferingSizes))
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.
SmallVector<unsigned, 4> TmpRetPath(RetPath.rbegin(), RetPath.rend());
SmallVector<unsigned, 4> TmpCallPath(CallPath.rbegin(), CallPath.rend());
// 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,
F->getParent()->getDataLayout()))
return false;
CallEmpty = !nextRealType(CallSubTypes, CallPath);
} while(nextRealType(RetSubTypes, RetPath));
return true;
}
bool llvm::canBeOmittedFromSymbolTable(const GlobalValue *GV) {
if (!GV->hasLinkOnceODRLinkage())
return false;
// We assume that anyone who sets global unnamed_addr on a non-constant knows
// what they're doing.
if (GV->hasGlobalUnnamedAddr())
return true;
// If it is a non constant variable, it needs to be uniqued across shared
// objects.
if (const GlobalVariable *Var = dyn_cast<GlobalVariable>(GV)) {
if (!Var->isConstant())
return false;
}
return GV->hasAtLeastLocalUnnamedAddr();
}
static void collectFuncletMembers(
DenseMap<const MachineBasicBlock *, int> &FuncletMembership, int Funclet,
const MachineBasicBlock *MBB) {
SmallVector<const MachineBasicBlock *, 16> Worklist = {MBB};
while (!Worklist.empty()) {
const MachineBasicBlock *Visiting = Worklist.pop_back_val();
// Don't follow blocks which start new funclets.
if (Visiting->isEHPad() && Visiting != MBB)
continue;
// Add this MBB to our funclet.
auto P = FuncletMembership.insert(std::make_pair(Visiting, Funclet));
// Don't revisit blocks.
if (!P.second) {
assert(P.first->second == Funclet && "MBB is part of two funclets!");
continue;
}
// Returns are boundaries where funclet transfer can occur, don't follow
// successors.
if (Visiting->isReturnBlock())
continue;
for (const MachineBasicBlock *Succ : Visiting->successors())
Worklist.push_back(Succ);
}
}
DenseMap<const MachineBasicBlock *, int>
llvm::getFuncletMembership(const MachineFunction &MF) {
DenseMap<const MachineBasicBlock *, int> FuncletMembership;
// We don't have anything to do if there aren't any EH pads.
if (!MF.getMMI().hasEHFunclets())
return FuncletMembership;
int EntryBBNumber = MF.front().getNumber();
bool IsSEH = isAsynchronousEHPersonality(
classifyEHPersonality(MF.getFunction()->getPersonalityFn()));
const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
SmallVector<const MachineBasicBlock *, 16> FuncletBlocks;
SmallVector<const MachineBasicBlock *, 16> UnreachableBlocks;
SmallVector<const MachineBasicBlock *, 16> SEHCatchPads;
SmallVector<std::pair<const MachineBasicBlock *, int>, 16> CatchRetSuccessors;
for (const MachineBasicBlock &MBB : MF) {
if (MBB.isEHFuncletEntry()) {
FuncletBlocks.push_back(&MBB);
} else if (IsSEH && MBB.isEHPad()) {
SEHCatchPads.push_back(&MBB);
} else if (MBB.pred_empty()) {
UnreachableBlocks.push_back(&MBB);
}
MachineBasicBlock::const_iterator MBBI = MBB.getFirstTerminator();
// CatchPads are not funclets for SEH so do not consider CatchRet to
// transfer control to another funclet.
if (MBBI == MBB.end() || MBBI->getOpcode() != TII->getCatchReturnOpcode())
continue;
// FIXME: SEH CatchPads are not necessarily in the parent function:
// they could be inside a finally block.
const MachineBasicBlock *Successor = MBBI->getOperand(0).getMBB();
const MachineBasicBlock *SuccessorColor = MBBI->getOperand(1).getMBB();
CatchRetSuccessors.push_back(
{Successor, IsSEH ? EntryBBNumber : SuccessorColor->getNumber()});
}
// We don't have anything to do if there aren't any EH pads.
if (FuncletBlocks.empty())
return FuncletMembership;
// Identify all the basic blocks reachable from the function entry.
collectFuncletMembers(FuncletMembership, EntryBBNumber, &MF.front());
// All blocks not part of a funclet are in the parent function.
for (const MachineBasicBlock *MBB : UnreachableBlocks)
collectFuncletMembers(FuncletMembership, EntryBBNumber, MBB);
// Next, identify all the blocks inside the funclets.
for (const MachineBasicBlock *MBB : FuncletBlocks)
collectFuncletMembers(FuncletMembership, MBB->getNumber(), MBB);
// SEH CatchPads aren't really funclets, handle them separately.
for (const MachineBasicBlock *MBB : SEHCatchPads)
collectFuncletMembers(FuncletMembership, EntryBBNumber, MBB);
// Finally, identify all the targets of a catchret.
for (std::pair<const MachineBasicBlock *, int> CatchRetPair :
CatchRetSuccessors)
collectFuncletMembers(FuncletMembership, CatchRetPair.second,
CatchRetPair.first);
return FuncletMembership;
}
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