[clang] [llvm] [VectorCombine] Trim low end of loads used in shufflevector rebroadcasts. (PR #149093)

[Simon Pilgrim via cfe-commits]

================
@@ -5475,8 +5479,14 @@ bool VectorCombine::shrinkLoadForShuffles(Instruction &I) {
         return false;
 
       // Create new load of smaller vector.
+      Type *IndexTy = DL->getIndexType(PtrOp->getType());
+      Value *NewPtr = LowOffset > 0u
+                          ? Builder.CreateInBoundsPtrAdd(
+                                PtrOp, ConstantInt::get(IndexTy, LowOffset))
+                          : PtrOp;
+
       auto *NewLoad = cast<LoadInst>(
-          Builder.CreateAlignedLoad(NewLoadTy, PtrOp, OldLoad->getAlign()));
+          Builder.CreateAlignedLoad(NewLoadTy, NewPtr, OldLoad->getAlign()));
----------------
RKSimon wrote:

@PeddleSpam You need to adjust the alignment as well

https://github.com/llvm/llvm-project/pull/149093