[Loads] Use more powerful constant folding API

This follows up on D111023 by exporting the generic "load value
from constant at given offset as given type" and using it in the
store to load forwarding code. We now need to make sure that the
load size is smaller than the store size, previously this was
implicitly ensured by ConstantFoldLoadThroughBitcast().

Differential Revision: https://reviews.llvm.org/D112260

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp
index 2e5f80d..1882e31 100644
--- a/llvm/lib/Analysis/Loads.cpp
+++ b/llvm/lib/Analysis/Loads.cpp
@@ -511,8 +511,11 @@ static Value *getAvailableLoadStore(Instruction *Inst, const Value *Ptr,
     if (CastInst::isBitOrNoopPointerCastable(Val->getType(), AccessTy, DL))
       return Val;
 
-    if (auto *C = dyn_cast<Constant>(Val))
-      return ConstantFoldLoadThroughBitcast(C, AccessTy, DL);
+    TypeSize StoreSize = DL.getTypeStoreSize(Val->getType());
+    TypeSize LoadSize = DL.getTypeStoreSize(AccessTy);
+    if (TypeSize::isKnownLE(LoadSize, StoreSize))
+      if (auto *C = dyn_cast<Constant>(Val))
+        return ConstantFoldLoadFromConst(C, AccessTy, DL);
   }
 
   return nullptr;