[GVNHoist] Properly merge alignments when hoisting

If we two loads of two different alignments, we must use the minimum of
the two alignments when hoisting.  Same deal for stores.

For allocas, use the maximum of the two allocas.

llvm-svn: 276601

1 files changed, 14 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Scalar/GVNHoist.cpp b/llvm/lib/Transforms/Scalar/GVNHoist.cpp
index e7179a342c2..0b5e94f8fb9 100644
--- a/llvm/lib/Transforms/Scalar/GVNHoist.cpp
+++ b/llvm/lib/Transforms/Scalar/GVNHoist.cpp
@@ -628,7 +628,6 @@ public:
             cast<Instruction>(cast<StoreInst>(OtherInst)->getValueOperand());
         ClonedVal->intersectOptionalDataWith(OtherVal);
       }
-      ClonedVal->clearSubclassOptionalData();
       Repl->replaceUsesOfWith(Val, ClonedVal);
     }
 
@@ -685,12 +684,23 @@ public:
       for (Instruction *I : InstructionsToHoist)
         if (I != Repl) {
           ++NR;
-          if (isa<LoadInst>(Repl))
+          if (auto *ReplacementLoad = dyn_cast<LoadInst>(Repl)) {
+            ReplacementLoad->setAlignment(
+                std::min(ReplacementLoad->getAlignment(),
+                         cast<LoadInst>(I)->getAlignment()));
             ++NumLoadsRemoved;
-          else if (isa<StoreInst>(Repl))
+          } else if (auto *ReplacementStore = dyn_cast<StoreInst>(Repl)) {
+            ReplacementStore->setAlignment(
+                std::min(ReplacementStore->getAlignment(),
+                         cast<StoreInst>(I)->getAlignment()));
             ++NumStoresRemoved;
-          else if (isa<CallInst>(Repl))
+          } else if (auto *ReplacementAlloca = dyn_cast<AllocaInst>(Repl)) {
+            ReplacementAlloca->setAlignment(
+                std::max(ReplacementAlloca->getAlignment(),
+                         cast<AllocaInst>(I)->getAlignment()));
+          } else if (isa<CallInst>(Repl)) {
             ++NumCallsRemoved;
+          }
           Repl->intersectOptionalDataWith(I);
           I->replaceAllUsesWith(Repl);
           I->eraseFromParent();