/// 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 Instruction *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;
// A lifetime end intrinsic should not stop tail call optimization.
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
if (II->getIntrinsicID() == Intrinsic::lifetime_end)
continue;
if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
!isSafeToSpeculativelyExecute(&*BBI))
return false;
}
const Function *F = ExitBB->getParent();
return returnTypeIsEligibleForTailCall(
F, I, Ret, *TM.getSubtargetImpl(*F)->getTargetLowering());
}
/// 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, Attribute CalleeRetAttr,
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();
Attribute CallerRetAttr = F->getAttributes().getRetAttributes();
if (AttrBuilder(CalleeRetAttr).removeAttribute(Attribute::NoAlias) !=
AttrBuilder(CallerRetAttr).removeAttribute(Attribute::NoAlias))
return false;
// It's not safe to eliminate the sign / zero extension of the return value.
if (CallerRetAttr.hasAttribute(Attribute::ZExt) ||
CallerRetAttr.hasAttribute(Attribute::SExt))
return false;
// Otherwise, make sure the unmodified return value of I is the return value.
// We handle two cases: multiple return values + scalars.
Value *RetVal = Ret->getOperand(0);
if (!isa<InsertValueInst>(RetVal) || !isa<StructType>(RetVal->getType()))
// Handle scalars first.
return getNoopInput(Ret->getOperand(0), TLI) == I;
// If this is an aggregate return, look through the insert/extract values and
// see if each is transparent.
for (unsigned i = 0, e =cast<StructType>(RetVal->getType())->getNumElements();
i != e; ++i) {
const Value *InScalar = FindInsertedValue(RetVal, i);
if (InScalar == 0) return false;
InScalar = getNoopInput(InScalar, TLI);
// If the scalar value being inserted is an extractvalue of the right index
// from the call, then everything is good.
const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(InScalar);
if (EVI == 0 || EVI->getOperand(0) != I || EVI->getNumIndices() != 1 ||
EVI->getIndices()[0] != i)
return false;
}
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, Attributes CalleeRetAttr,
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 &&
(!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() ||
!I->isSafeToSpeculativelyExecute())
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() ||
!BBI->isSafeToSpeculativelyExecute())
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();
unsigned CallerRetAttr = F->getAttributes().getRetAttributes();
if ((CalleeRetAttr ^ CallerRetAttr) & ~Attribute::NoAlias)
return false;
// It's not safe to eliminate the sign / zero extension of the return value.
if ((CallerRetAttr & Attribute::ZExt) || (CallerRetAttr & Attribute::SExt))
return false;
// Otherwise, make sure the unmodified return value of I is the return value.
for (const Instruction *U = dyn_cast<Instruction>(Ret->getOperand(0)); ;
U = dyn_cast<Instruction>(U->getOperand(0))) {
if (!U)
return false;
if (!U->hasOneUse())
return false;
if (U == I)
break;
// Check for a truly no-op truncate.
if (isa<TruncInst>(U) &&
TLI.isTruncateFree(U->getOperand(0)->getType(), U->getType()))
continue;
// Check for a truly no-op bitcast.
if (isa<BitCastInst>(U) &&
(U->getOperand(0)->getType() == U->getType() ||
(U->getOperand(0)->getType()->isPointerTy() &&
U->getType()->isPointerTy())))
continue;
// Otherwise it's not a true no-op.
return false;
}
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;
}
// 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(ExitBB->getParent()->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;
}