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Factor the profitability check for return slot optimization out into a static function.

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At some point in the future, this check will become smarter.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47310 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2008-02-19 03:27:34 +00:00
parent c0755a6f98
commit fa113f8155
1 changed files with 26 additions and 14 deletions
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40
lib/Transforms/Scalar/GVN.cpp
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@ -1052,6 +1052,28 @@ bool GVN::processLoad(LoadInst* L,
return deletedLoad;
}
/// isReturnSlotOptznProfitable - Determine if performing a return slot
/// fusion with the slot dest is profitable
static bool isReturnSlotOptznProfitable(Value* dest, MemCpyInst* cpy) {
// We currently consider it profitable if dest is otherwise dead.
SmallVector<User*, 8> useList(dest->use_begin(), dest->use_end());
while (!useList.empty()) {
User* UI = useList.back();
if (isa<GetElementPtrInst>(UI) || isa<BitCastInst>(UI)) {
useList.pop_back();
for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
I != E; ++I)
useList.push_back(*I);
} else if (UI == cpy)
useList.pop_back();
else
return false;
}
return true;
}
/// performReturnSlotOptzn - takes a memcpy and a call that it depends on,
/// and checks for the possibility of a return slot optimization by having
/// the call write its result directly into the callees return parameter
@ -1068,26 +1090,16 @@ bool GVN::performReturnSlotOptzn(MemCpyInst* cpy, CallInst* C,
if (!sretArg->hasStructRetAttr())
return false;
// Make sure the return slot is otherwise dead
std::set<User*> useList(sretArg->use_begin(), sretArg->use_end());
while (!useList.empty()) {
User* UI = *useList.begin();
if (isa<GetElementPtrInst>(UI) || isa<BitCastInst>(UI)) {
useList.insert(UI->use_begin(), UI->use_end());
useList.erase(UI);
} else if (UI == cpy)
useList.erase(UI);
else
return false;
}
// We only perform the transformation if it will be profitable.
if (!isReturnSlotOptznProfitable(sretArg, cpy))
return false;
// Make sure the call cannot modify the return slot in some unpredicted way
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
if (AA.getModRefInfo(C, cpy->getRawDest(), ~0UL) != AliasAnalysis::NoModRef)
return false;
// If all checks passed, then we can perform the transformation
// If all checks passed, then we can perform the transformation.
CallSite CS = CallSite::get(C);
if (CS.getArgument(0)->getType() != cpyDest->getType())
return false;