[InstCombine] Don't widen metadata on store-to-load forwarding

The original check for load CSE or store-to-load forwarding is wrong when the forwarded stored value happened to be a load. Ref JuliaLang/julia#16894 Differential Revision: http://reviews.llvm.org/D21271 Patch by Yichao Yu! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272868 91177308-0d34-0410-b5e6-96231b3b80d8
earl · Jun 16, 2016 · 4721ee1 · 4721ee1
1 parent 6f40146
commit 4721ee1
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Showing 4 changed files with 27 additions and 4 deletions.
diff --git a/include/llvm/Analysis/Loads.h b/include/llvm/Analysis/Loads.h
@@ -82,7 +82,8 @@ Value *FindAvailableLoadedValue(LoadInst *Load, BasicBlock *ScanBB,
                                 BasicBlock::iterator &ScanFrom,
                                 unsigned MaxInstsToScan = DefMaxInstsToScan,
                                 AliasAnalysis *AA = nullptr,
-                                AAMDNodes *AATags = nullptr);
+                                AAMDNodes *AATags = nullptr,
+                                bool *IsLoadCSE = nullptr);
 
 }
 

diff --git a/lib/Analysis/Loads.cpp b/lib/Analysis/Loads.cpp
@@ -322,7 +322,8 @@ llvm::DefMaxInstsToScan("available-load-scan-limit", cl::init(6), cl::Hidden,
 Value *llvm::FindAvailableLoadedValue(LoadInst *Load, BasicBlock *ScanBB,
                                       BasicBlock::iterator &ScanFrom,
                                       unsigned MaxInstsToScan,
-                                      AliasAnalysis *AA, AAMDNodes *AATags) {
+                                      AliasAnalysis *AA, AAMDNodes *AATags,
+                                      bool *IsLoadCSE) {
   if (MaxInstsToScan == 0)
     MaxInstsToScan = ~0U;
 
@@ -374,6 +375,8 @@ Value *llvm::FindAvailableLoadedValue(LoadInst *Load, BasicBlock *ScanBB,
 
         if (AATags)
           LI->getAAMetadata(*AATags);
+        if (IsLoadCSE)
+            *IsLoadCSE = true;
         return LI;
       }
 

diff --git a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -819,10 +819,12 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
   // separated by a few arithmetic operations.
   BasicBlock::iterator BBI(LI);
   AAMDNodes AATags;
+  bool IsLoadCSE = false;
   if (Value *AvailableVal =
       FindAvailableLoadedValue(&LI, LI.getParent(), BBI,
-                               DefMaxInstsToScan, AA, &AATags)) {
-    if (LoadInst *NLI = dyn_cast<LoadInst>(AvailableVal)) {
+                               DefMaxInstsToScan, AA, &AATags, &IsLoadCSE)) {
+    if (IsLoadCSE) {
+      LoadInst *NLI = cast<LoadInst>(AvailableVal);
       unsigned KnownIDs[] = {
           LLVMContext::MD_tbaa,            LLVMContext::MD_alias_scope,
           LLVMContext::MD_noalias,         LLVMContext::MD_range,

diff --git a/test/Transforms/InstCombine/tbaa-store-to-load.ll b/test/Transforms/InstCombine/tbaa-store-to-load.ll
@@ -0,0 +1,17 @@
+; RUN: opt -S -instcombine < %s 2>&1 | FileCheck %s
+
+define i64 @f(i64* %p1, i64* %p2) {
+top:
+  ; check that the tbaa is preserved
+  ; CHECK-LABEL: @f(
+  ; CHECK: %v1 = load i64, i64* %p1, align 8, !tbaa !0
+  ; CHECK: store i64 %v1, i64* %p2, align 8
+  ; CHECK: ret i64 %v1
+  %v1 = load i64, i64* %p1, align 8, !tbaa !0
+  store i64 %v1, i64* %p2, align 8
+  %v2 = load i64, i64* %p2, align 8
+  ret i64 %v2
+}
+
+!0 = !{!1, !1, i64 0}
+!1 = !{!"load_tbaa"}