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Move isInTailCallPosition out of SelectionDAGBuilder, as it isn't
SelectionDAG-specific. llvm-svn: 101801
This commit is contained in:
Dan Gohman
parent
c9fe920296
commit
3c58144bfd
@ -448,3 +448,88 @@ ISD::CondCode llvm::getICmpCondCode(ICmpInst::Predicate Pred) {
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return ISD::SETNE;
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}
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}
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/// Test if the given instruction is in a position to be optimized
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/// with a tail-call. This roughly means that it's in a block with
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/// a return and there's nothing that needs to be scheduled
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/// between it and the return.
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///
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/// This function only tests target-independent requirements.
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bool llvm::isInTailCallPosition(ImmutableCallSite CS, Attributes CalleeRetAttr,
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const TargetLowering &TLI) {
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const Instruction *I = CS.getInstruction();
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const BasicBlock *ExitBB = I->getParent();
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const TerminatorInst *Term = ExitBB->getTerminator();
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const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
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const Function *F = ExitBB->getParent();
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// The block must end in a return statement or unreachable.
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//
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// FIXME: Decline tailcall if it's not guaranteed and if the block ends in
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// an unreachable, for now. The way tailcall optimization is currently
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// implemented means it will add an epilogue followed by a jump. That is
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// not profitable. Also, if the callee is a special function (e.g.
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// longjmp on x86), it can end up causing miscompilation that has not
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// been fully understood.
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if (!Ret &&
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(!GuaranteedTailCallOpt || !isa<UnreachableInst>(Term))) return false;
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// If I will have a chain, make sure no other instruction that will have a
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// chain interposes between I and the return.
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if (I->mayHaveSideEffects() || I->mayReadFromMemory() ||
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!I->isSafeToSpeculativelyExecute())
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for (BasicBlock::const_iterator BBI = prior(prior(ExitBB->end())); ;
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--BBI) {
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if (&*BBI == I)
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break;
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// Debug info intrinsics do not get in the way of tail call optimization.
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if (isa<DbgInfoIntrinsic>(BBI))
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continue;
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if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
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!BBI->isSafeToSpeculativelyExecute())
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return false;
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}
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// If the block ends with a void return or unreachable, it doesn't matter
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// what the call's return type is.
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if (!Ret || Ret->getNumOperands() == 0) return true;
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// If the return value is undef, it doesn't matter what the call's
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// return type is.
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if (isa<UndefValue>(Ret->getOperand(0))) return true;
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// Conservatively require the attributes of the call to match those of
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// the return. Ignore noalias because it doesn't affect the call sequence.
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unsigned CallerRetAttr = F->getAttributes().getRetAttributes();
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if ((CalleeRetAttr ^ CallerRetAttr) & ~Attribute::NoAlias)
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return false;
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// It's not safe to eliminate the sign / zero extension of the return value.
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if ((CallerRetAttr & Attribute::ZExt) || (CallerRetAttr & Attribute::SExt))
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return false;
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// Otherwise, make sure the unmodified return value of I is the return value.
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for (const Instruction *U = dyn_cast<Instruction>(Ret->getOperand(0)); ;
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U = dyn_cast<Instruction>(U->getOperand(0))) {
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if (!U)
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return false;
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if (!U->hasOneUse())
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return false;
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if (U == I)
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break;
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// Check for a truly no-op truncate.
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if (isa<TruncInst>(U) &&
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TLI.isTruncateFree(U->getOperand(0)->getType(), U->getType()))
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continue;
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// Check for a truly no-op bitcast.
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if (isa<BitCastInst>(U) &&
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(U->getOperand(0)->getType() == U->getType() ||
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(U->getOperand(0)->getType()->isPointerTy() &&
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U->getType()->isPointerTy())))
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continue;
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// Otherwise it's not a true no-op.
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return false;
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}
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return true;
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}
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@ -24,6 +24,7 @@
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#endif
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#include "llvm/CodeGen/ValueTypes.h"
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#include "llvm/CodeGen/ISDOpcodes.h"
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#include "llvm/Support/CallSite.h"
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#include <vector>
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namespace llvm {
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@ -166,6 +167,15 @@ ISD::CondCode getFCmpCondCode(FCmpInst::Predicate Pred);
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///
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ISD::CondCode getICmpCondCode(ICmpInst::Predicate Pred);
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/// Test if the given instruction is in a position to be optimized
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/// with a tail-call. This roughly means that it's in a block with
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/// a return and there's nothing that needs to be scheduled
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/// between it and the return.
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///
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/// This function only tests target-independent requirements.
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bool isInTailCallPosition(ImmutableCallSite CS, Attributes CalleeRetAttr,
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const TargetLowering &TLI);
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} // end namespace llvm
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#endif
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@ -4190,92 +4190,6 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
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}
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}
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/// Test if the given instruction is in a position to be optimized
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/// with a tail-call. This roughly means that it's in a block with
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/// a return and there's nothing that needs to be scheduled
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/// between it and the return.
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///
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/// This function only tests target-independent requirements.
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static bool
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isInTailCallPosition(ImmutableCallSite CS, Attributes CalleeRetAttr,
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const TargetLowering &TLI) {
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const Instruction *I = CS.getInstruction();
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const BasicBlock *ExitBB = I->getParent();
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const TerminatorInst *Term = ExitBB->getTerminator();
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const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
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const Function *F = ExitBB->getParent();
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// The block must end in a return statement or unreachable.
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//
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// FIXME: Decline tailcall if it's not guaranteed and if the block ends in
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// an unreachable, for now. The way tailcall optimization is currently
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// implemented means it will add an epilogue followed by a jump. That is
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// not profitable. Also, if the callee is a special function (e.g.
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// longjmp on x86), it can end up causing miscompilation that has not
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// been fully understood.
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if (!Ret &&
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(!GuaranteedTailCallOpt || !isa<UnreachableInst>(Term))) return false;
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// If I will have a chain, make sure no other instruction that will have a
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// chain interposes between I and the return.
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if (I->mayHaveSideEffects() || I->mayReadFromMemory() ||
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!I->isSafeToSpeculativelyExecute())
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for (BasicBlock::const_iterator BBI = prior(prior(ExitBB->end())); ;
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--BBI) {
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if (&*BBI == I)
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break;
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// Debug info intrinsics do not get in the way of tail call optimization.
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if (isa<DbgInfoIntrinsic>(BBI))
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continue;
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if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
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!BBI->isSafeToSpeculativelyExecute())
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return false;
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}
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// If the block ends with a void return or unreachable, it doesn't matter
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// what the call's return type is.
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if (!Ret || Ret->getNumOperands() == 0) return true;
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// If the return value is undef, it doesn't matter what the call's
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// return type is.
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if (isa<UndefValue>(Ret->getOperand(0))) return true;
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// Conservatively require the attributes of the call to match those of
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// the return. Ignore noalias because it doesn't affect the call sequence.
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unsigned CallerRetAttr = F->getAttributes().getRetAttributes();
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if ((CalleeRetAttr ^ CallerRetAttr) & ~Attribute::NoAlias)
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return false;
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// It's not safe to eliminate the sign / zero extension of the return value.
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if ((CallerRetAttr & Attribute::ZExt) || (CallerRetAttr & Attribute::SExt))
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return false;
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// Otherwise, make sure the unmodified return value of I is the return value.
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for (const Instruction *U = dyn_cast<Instruction>(Ret->getOperand(0)); ;
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U = dyn_cast<Instruction>(U->getOperand(0))) {
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if (!U)
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return false;
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if (!U->hasOneUse())
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return false;
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if (U == I)
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break;
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// Check for a truly no-op truncate.
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if (isa<TruncInst>(U) &&
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TLI.isTruncateFree(U->getOperand(0)->getType(), U->getType()))
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continue;
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// Check for a truly no-op bitcast.
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if (isa<BitCastInst>(U) &&
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(U->getOperand(0)->getType() == U->getType() ||
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(U->getOperand(0)->getType()->isPointerTy() &&
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U->getType()->isPointerTy())))
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continue;
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// Otherwise it's not a true no-op.
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return false;
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}
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return true;
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}
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void SelectionDAGBuilder::LowerCallTo(ImmutableCallSite CS, SDValue Callee,
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bool isTailCall,
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MachineBasicBlock *LandingPad) {
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