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a byval argument is guaranteed to be valid to load. 

llvm-svn: 45877
This commit is contained in:
Chris Lattner 2008-01-11 19:34:32 +00:00
parent 4062a625e5
commit 4a70261f00
1 changed files with 19 additions and 4 deletions
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23
llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
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@ -193,7 +193,15 @@ static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) {
bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const {
// We can only promote this argument if all of the uses are loads, or are GEP
// instructions (with constant indices) that are subsequently loaded.
bool HasLoadInEntryBlock = false;
// We can also only promote the load if we can guarantee that it will happen.
// Promoting a load causes the load to be unconditionally executed in the
// caller, so we can't turn a conditional load into an unconditional load in
// general.
bool SafeToUnconditionallyLoad = false;
if (isByVal) // ByVal arguments are always safe to load from.
SafeToUnconditionallyLoad = true;
BasicBlock *EntryBlock = Arg->getParent()->begin();
SmallVector<LoadInst*, 16> Loads;
std::vector<SmallVector<ConstantInt*, 8> > GEPIndices;
@ -202,7 +210,10 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const {
if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
if (LI->isVolatile()) return false; // Don't hack volatile loads
Loads.push_back(LI);
HasLoadInEntryBlock |= LI->getParent() == EntryBlock;
// If this load occurs in the entry block, then the pointer is
// unconditionally loaded.
SafeToUnconditionallyLoad |= LI->getParent() == EntryBlock;
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
if (GEP->use_empty()) {
// Dead GEP's cause trouble later. Just remove them if we run into
@ -225,7 +236,10 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const {
if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
if (LI->isVolatile()) return false; // Don't hack volatile loads
Loads.push_back(LI);
HasLoadInEntryBlock |= LI->getParent() == EntryBlock;
// If this load occurs in the entry block, then the pointer is
// unconditionally loaded.
SafeToUnconditionallyLoad |= LI->getParent() == EntryBlock;
} else {
return false;
}
@ -257,7 +271,8 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const {
// of the pointer in the entry block of the function) or if we can prove that
// all pointers passed in are always to legal locations (for example, no null
// pointers are passed in, no pointers to free'd memory, etc).
if (!HasLoadInEntryBlock && !AllCalleesPassInValidPointerForArgument(Arg))
if (!SafeToUnconditionallyLoad &&
!AllCalleesPassInValidPointerForArgument(Arg))
return false; // Cannot prove that this is safe!!
// Okay, now we know that the argument is only used by load instructions and