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If call result is in ST0 and it is not being passed to the caller's 

caller, then it is not safe to optimize the call into a sibcall since
the call result has to be popped off the x87 stack.

llvm-svn: 99032
This commit is contained in:
Evan Cheng 2010-03-20 02:58:15 +00:00
parent 5ea5fab22b
commit 3f6f769c4f
1 changed files with 22 additions and 0 deletions
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22
llvm/lib/Target/X86/X86ISelLowering.cpp
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@ -2310,6 +2310,28 @@ X86TargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
if (isCalleeStructRet || isCallerStructRet)
return false;
// If the call result is in ST0 / ST1, it needs to be popped off the x87 stack.
// Therefore if it's not used by the call it is not safe to optimize this into
// a sibcall.
bool Unused = false;
for (unsigned i = 0, e = Ins.size(); i != e; ++i) {
if (!Ins[i].Used) {
Unused = true;
break;
}
}
if (Unused) {
SmallVector<CCValAssign, 16> RVLocs;
CCState CCInfo(CalleeCC, false, getTargetMachine(),
RVLocs, *DAG.getContext());
CCInfo.AnalyzeCallResult(Ins, RetCC_X86);
for (unsigned i = 0; i != RVLocs.size(); ++i) {
CCValAssign &VA = RVLocs[i];
if (VA.getLocReg() == X86::ST0 || VA.getLocReg() == X86::ST1)
return false;
}
}
// If the callee takes no arguments then go on to check the results of the
// call.
if (!Outs.empty()) {