teach instcombine to preserve TBAA tag when merging two stores, part of

PR14753

llvm-svn: 171279

2 files changed, 41 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 5726d3a91de..ca069572812 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -802,6 +802,13 @@ bool InstCombiner::SimplifyStoreAtEndOfBlock(StoreInst &SI) {
   InsertNewInstBefore(NewSI, *BBI);
   NewSI->setDebugLoc(OtherStore->getDebugLoc()); 
 
+  // If the two stores had the same TBAA tag, preserve it.
+  if (MDNode *TBAATag1 = SI.getMetadata(LLVMContext::MD_tbaa))
+    if (MDNode *TBAATag2 = OtherStore->getMetadata(LLVMContext::MD_tbaa))
+      if (TBAATag1 == TBAATag2)
+        NewSI->setMetadata(LLVMContext::MD_tbaa, TBAATag1);
+
+  
   // Nuke the old stores.
   EraseInstFromFunction(SI);
   EraseInstFromFunction(*OtherStore);
diff --git a/llvm/test/Transforms/InstCombine/store.ll b/llvm/test/Transforms/InstCombine/store.ll
index 64460d7a6d6..164ba763268 100644
--- a/llvm/test/Transforms/InstCombine/store.ll
+++ b/llvm/test/Transforms/InstCombine/store.ll
@@ -83,3 +83,37 @@ Cont:
 ; CHECK-NEXT:  ret void
 }
 
+
+; PR14753 - merging two stores should preserve the TBAA tag.
+define void @test6(i32 %n, float* %a, i32* %gi) nounwind uwtable ssp {
+entry:
+  store i32 42, i32* %gi, align 4, !tbaa !0
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.body, %entry
+  %storemerge = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  %0 = load i32* %gi, align 4, !tbaa !0
+  %cmp = icmp slt i32 %0, %n
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %idxprom = sext i32 %0 to i64
+  %arrayidx = getelementptr inbounds float* %a, i64 %idxprom
+  store float 0.000000e+00, float* %arrayidx, align 4, !tbaa !3
+  %1 = load i32* %gi, align 4, !tbaa !0
+  %inc = add nsw i32 %1, 1
+  store i32 %inc, i32* %gi, align 4, !tbaa !0
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  ret void
+; CHECK: @test6
+; CHECK: for.cond:
+; CHECK-NEXT: phi i32 [ 42
+; CHECK-NEXT: store i32 %storemerge, i32* %gi, align 4, !tbaa !0
+}
+
+!0 = metadata !{metadata !"int", metadata !1}
+!1 = metadata !{metadata !"omnipotent char", metadata !2}
+!2 = metadata !{metadata !"Simple C/C++ TBAA"}
+!3 = metadata !{metadata !"float", metadata !1}