a byval argument is guaranteed to be valid to load.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45877 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/IPO/ArgumentPromotion.cpp b/lib/Transforms/IPO/ArgumentPromotion.cpp
index 42a7067..1c739ad 100644
--- a/lib/Transforms/IPO/ArgumentPromotion.cpp
+++ b/lib/Transforms/IPO/ArgumentPromotion.cpp
@@ -193,7 +193,15 @@
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 @@
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 @@
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 @@
// 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