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Make DeadArgumentElimination more conservative on variadic functions

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Variadic functions are particularly fragile in the face of ABI changes, so this
limits how much the pass changes them

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183625 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Tim Northover
2013-06-09 02:17:27 +00:00
parent 1fe907e7f2
commit d84b17e157
2 changed files with 55 additions and 5 deletions
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22
lib/Transforms/IPO/DeadArgumentElimination.cpp
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@@ -343,8 +343,9 @@ bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
if (Fn.isDeclaration() || Fn.mayBeOverridden())
return false;
// Functions with local linkage should already have been handled.
if (Fn.hasLocalLinkage())
// Functions with local linkage should already have been handled, except the
// fragile (variadic) ones which we can improve here.
if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
return false;
if (Fn.use_empty())
@@ -604,9 +605,20 @@ void DAE::SurveyFunction(const Function &F) {
UseVector MaybeLiveArgUses;
for (Function::const_arg_iterator AI = F.arg_begin(),
E = F.arg_end(); AI != E; ++AI, ++i) {
// See what the effect of this use is (recording any uses that cause
// MaybeLive in MaybeLiveArgUses).
Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
Liveness Result;
if (F.getFunctionType()->isVarArg()) {
// Variadic functions will already have a va_arg function expanded inside
// them, making them potentially very sensitive to ABI changes resulting
// from removing arguments entirely, so don't. For example AArch64 handles
// register and stack HFAs very differently, and this is reflected in the
// IR which has already been generated.
Result = Live;
} else {
// See what the effect of this use is (recording any uses that cause
// MaybeLive in MaybeLiveArgUses).
Result = SurveyUses(AI, MaybeLiveArgUses);
}
// Mark the result.
MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
// Clear the vector again for the next iteration.