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It's too risky to eliminate sext / zext of call results for tail call optimization even if the caller / callee attributes completely match. The callee may have been bitcast'ed (or otherwise lied about what it's doing).

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95282 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2010-02-04 02:45:02 +00:00
parent 32efba698d
commit 446bc10085
1 changed files with 4 additions and 6 deletions
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10
lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
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@ -4213,12 +4213,6 @@ isInTailCallPosition(CallSite CS, Attributes CalleeRetAttr,
// causing miscompilation that has not been fully understood.
if (!Ret) return false;
// Unless we are explicitly forcing tailcall optimization do not tailcall if
// the called function is bitcast'ed. The analysis may not be entirely
// accurate.
if (!PerformTailCallOpt && isa<BitCastInst>(CS.getCalledValue()))
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() ||
@ -4246,6 +4240,10 @@ isInTailCallPosition(CallSite CS, Attributes CalleeRetAttr,
if ((CalleeRetAttr ^ CallerRetAttr) & ~Attribute::NoAlias)
return false;
// It's not safe to eliminate thee 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))) {