[PATCH] D103419: [VectorCombine] Fix alignment in single element store

[Qiu Chaofan via Phabricator via llvm-commits]

qiucf created this revision.
qiucf added reviewers: lebedev.ri, fhahn, spatel, efriedma, hgreving.
Herald added a subscriber: hiraditya.
qiucf requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

This concern was raised in D98240 <https://reviews.llvm.org/D98240>. It's a miscompile and thanks for comments from @lebedev.ri.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D103419

Files:
  llvm/lib/Transforms/Vectorize/VectorCombine.cpp
  llvm/test/Transforms/VectorCombine/load-insert-store.ll


Index: llvm/test/Transforms/VectorCombine/load-insert-store.ll
===================================================================
--- llvm/test/Transforms/VectorCombine/load-insert-store.ll
+++ llvm/test/Transforms/VectorCombine/load-insert-store.ll
@@ -20,7 +20,7 @@
 ; CHECK-LABEL: @insert_store_i16_align1(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds <8 x i16>, <8 x i16>* [[Q:%.*]], i32 0, i32 3
-; CHECK-NEXT:    store i16 [[S:%.*]], i16* [[TMP0]], align 1
+; CHECK-NEXT:    store i16 [[S:%.*]], i16* [[TMP0]], align 2
 ; CHECK-NEXT:    ret void
 ;
 entry:
Index: llvm/lib/Transforms/Vectorize/VectorCombine.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -831,8 +831,14 @@
     Builder.Insert(GEP);
     StoreInst *NSI = Builder.CreateStore(NewElement, GEP);
     NSI->copyMetadata(*SI);
-    if (SI->getAlign() < NSI->getAlign())
-      NSI->setAlignment(SI->getAlign());
+    Align NewAlignment(1);
+    if (auto *C = dyn_cast<ConstantInt>(Idx)) {
+      NewAlignment = std::max(SI->getAlign(), Load->getAlign());
+      NewAlignment = commonAlignment(
+          NewAlignment,
+          C->getZExtValue() * DL.getTypeStoreSize(NewElement->getType()));
+    }
+    NSI->setAlignment(NewAlignment);
     replaceValue(I, *NSI);
     // Need erasing the store manually.
     I.eraseFromParent();


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