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llvm-6502/lib/CodeGen/Analysis.cpp
Stephen Lin 13aba14eb5 Add some constraints to use of 'returned': 
1) Disallow 'returned' on parameter that is also 'sret' (no sensible semantics, as far as I can tell).
2) Conservatively disallow tail calls through 'returned' parameters that also are 'zext' or 'sext' (for consistency with treatment of other zero-extending and sign-extending operations in tail call position detection...can be revised later to handle situations that can be determined to be safe).

This is a new attribute that is not yet used, so there is no impact.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180118 91177308-0d34-0410-b5e6-96231b3b80d8
2013-04-23 16:31:56 +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 TargetLowering& TLI) {
return T1 == T2 || (T1->isPointerTy() && T2->isPointerTy()) ||
(isa<VectorType>(T1) && isa<VectorType>(T2) &&
TLI.isTypeLegal(EVT::getEVT(T1)) && TLI.isTypeLegal(EVT::getEVT(T2)));
}
/// sameNoopInput - Return true if V1 == V2, else if either V1 or V2 is a noop
/// (i.e., lowers to no machine code), look through it (and any transitive noop
/// operands to it) and check if it has the same noop input value. This is
/// used to determine if a tail call can be formed.
static bool sameNoopInput(const Value *V1, const Value *V2,
SmallVectorImpl<unsigned> &Els1,
SmallVectorImpl<unsigned> &Els2,
const TargetLowering &TLI) {
using std::swap;
bool swapParity = false;
bool equalEls = Els1 == Els2;
while (true) {
if ((equalEls && V1 == V2) || isa<UndefValue>(V1) || isa<UndefValue>(V2)) {
if (swapParity)
// Revert to original Els1 and Els2 to avoid confusing recursive calls
swap(Els1, Els2);
return true;
}
// Try to look through V1; if V1 is not an instruction, it can't be looked
// through.
const Instruction *I = dyn_cast<Instruction>(V1);
const Value *NoopInput = 0;
if (I != 0 && I->getNumOperands() > 0) {
Value *Op = I->getOperand(0);
if (isa<TruncInst>(I)) {
// Look through truly no-op truncates.
if (TLI.isTruncateFree(Op->getType(), I->getType()))
NoopInput = Op;
} else 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<CallInst>(I)) {
// Look through call
for (User::const_op_iterator i = I->op_begin(),
// Skip Callee
e = I->op_end() - 1;
i != e; ++i) {
unsigned attrInd = i - I->op_begin() + 1;
if (cast<CallInst>(I)->paramHasAttr(attrInd, Attribute::Returned) &&
!cast<CallInst>(I)->paramHasAttr(attrInd, Attribute::ZExt) &&
!cast<CallInst>(I)->paramHasAttr(attrInd, Attribute::SExt) &&
isNoopBitcast((*i)->getType(), I->getType(), TLI)) {
NoopInput = *i;
break;
}
}
} else if (isa<InvokeInst>(I)) {
// Look through invoke
for (User::const_op_iterator i = I->op_begin(),
// Skip BB, BB, Callee
e = I->op_end() - 3;
i != e; ++i) {
unsigned attrInd = i - I->op_begin() + 1;
if (cast<InvokeInst>(I)->paramHasAttr(attrInd, Attribute::Returned) &&
!cast<InvokeInst>(I)->paramHasAttr(attrInd, Attribute::ZExt) &&
!cast<InvokeInst>(I)->paramHasAttr(attrInd, Attribute::SExt) &&
isNoopBitcast((*i)->getType(), I->getType(), TLI)) {
NoopInput = *i;
break;
}
}
}
}
if (NoopInput) {
V1 = NoopInput;
continue;
}
// If we already swapped, avoid infinite loop
if (swapParity)
break;
// Otherwise, swap V1<->V2, Els1<->Els2
swap(V1, V2);
swap(Els1, Els2);
swapParity = !swapParity;
}
for (unsigned n = 0; n < 2; ++n) {
if (isa<InsertValueInst>(V1)) {
if (isa<StructType>(V1->getType())) {
// Look through insertvalue
unsigned i, e;
for (i = 0, e = cast<StructType>(V1->getType())->getNumElements();
i != e; ++i) {
const Value *InScalar = FindInsertedValue(const_cast<Value*>(V1), i);
if (InScalar == 0)
break;
Els1.push_back(i);
if (!sameNoopInput(InScalar, V2, Els1, Els2, TLI)) {
Els1.pop_back();
break;
}
Els1.pop_back();
}
if (i == e) {
if (swapParity)
swap(Els1, Els2);
return true;
}
}
} else if (!Els1.empty() && isa<ExtractValueInst>(V1)) {
const ExtractValueInst *EVI = cast<ExtractValueInst>(V1);
unsigned i = Els1.back();
// If the scalar value being inserted is an extractvalue of the right
// index from the call, then everything is good.
if (isa<StructType>(EVI->getOperand(0)->getType()) &&
EVI->getNumIndices() == 1 && EVI->getIndices()[0] == i) {
// Look through extractvalue
Els1.pop_back();
if (sameNoopInput(EVI->getOperand(0), V2, Els1, Els2, TLI)) {
Els1.push_back(i);
if (swapParity)
swap(Els1, Els2);
return true;
}
Els1.push_back(i);
}
}
swap(V1, V2);
swap(Els1, Els2);
swapParity = !swapParity;
}
if (swapParity)
swap(Els1, Els2);
return false;
}
/// 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;
}
// 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;
// Conservatively require the attributes of the call to match those of
// the return. Ignore noalias because it doesn't affect the call sequence.
const Function *F = ExitBB->getParent();
AttributeSet CallerAttrs = F->getAttributes();
if (AttrBuilder(CallerAttrs, AttributeSet::ReturnIndex).
removeAttribute(Attribute::NoAlias) !=
AttrBuilder(CallerAttrs, AttributeSet::ReturnIndex).
removeAttribute(Attribute::NoAlias))
return false;
// It's not safe to eliminate the sign / zero extension of the return value.
if (CallerAttrs.hasAttribute(AttributeSet::ReturnIndex, Attribute::ZExt) ||
CallerAttrs.hasAttribute(AttributeSet::ReturnIndex, Attribute::SExt))
return false;
// Otherwise, make sure the return value and I have the same value
SmallVector<unsigned, 4> Els1, Els2;
return sameNoopInput(Ret->getOperand(0), I, Els1, Els2, TLI);
}
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