[llvm] r272868 - [InstCombine] Don't widen metadata on store-to-load forwarding

[Eli Friedman via llvm-commits]

Author: efriedma
Date: Wed Jun 15 21:33:42 2016
New Revision: 272868

URL: http://llvm.org/viewvc/llvm-project?rev=272868&view=rev
Log:
[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 https://github.com/JuliaLang/julia/issues/16894

Differential Revision: http://reviews.llvm.org/D21271

Patch by Yichao Yu!

Added:
    llvm/trunk/test/Transforms/InstCombine/tbaa-store-to-load.ll
Modified:
    llvm/trunk/include/llvm/Analysis/Loads.h
    llvm/trunk/lib/Analysis/Loads.cpp
    llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

Modified: llvm/trunk/include/llvm/Analysis/Loads.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/Loads.h?rev=272868&r1=272867&r2=272868&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/Loads.h (original)
+++ llvm/trunk/include/llvm/Analysis/Loads.h Wed Jun 15 21:33:42 2016
@@ -82,7 +82,8 @@ Value *FindAvailableLoadedValue(LoadInst
                                 BasicBlock::iterator &ScanFrom,
                                 unsigned MaxInstsToScan = DefMaxInstsToScan,
                                 AliasAnalysis *AA = nullptr,
-                                AAMDNodes *AATags = nullptr);
+                                AAMDNodes *AATags = nullptr,
+                                bool *IsLoadCSE = nullptr);
 
 }
 

Modified: llvm/trunk/lib/Analysis/Loads.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/Loads.cpp?rev=272868&r1=272867&r2=272868&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/Loads.cpp (original)
+++ llvm/trunk/lib/Analysis/Loads.cpp Wed Jun 15 21:33:42 2016
@@ -322,7 +322,8 @@ llvm::DefMaxInstsToScan("available-load-
 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(Lo
 
         if (AATags)
           LI->getAAMetadata(*AATags);
+        if (IsLoadCSE)
+            *IsLoadCSE = true;
         return LI;
       }
 

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp?rev=272868&r1=272867&r2=272868&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp Wed Jun 15 21:33:42 2016
@@ -819,10 +819,12 @@ Instruction *InstCombiner::visitLoadInst
   // 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,

Added: llvm/trunk/test/Transforms/InstCombine/tbaa-store-to-load.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/tbaa-store-to-load.ll?rev=272868&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/tbaa-store-to-load.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/tbaa-store-to-load.ll Wed Jun 15 21:33:42 2016
@@ -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"}