From 3c80c2658022201214241e9229ac35097cc476d2 Mon Sep 17 00:00:00 2001

From: Eli Friedman <eli.friedman@gmail.com>

Date: Thu, 16 Jun 2016 02:33:42 +0000

Subject: [PATCH] [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!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272868 91177308-0d34-0410-b5e6-96231b3b80d8

Alpine maintainer notes:

  - Updated for llvm 3.8.1.

  - Corresponds to llvm-D21271-instcombine-tbaa-3.8.patch in Julia.

---

 include/llvm/Analysis/Loads.h                           |  3 ++-

 lib/Analysis/Loads.cpp                                  |  5 ++++-

 .../InstCombine/InstCombineLoadStoreAlloca.cpp          |  6 ++++--

 test/Transforms/InstCombine/tbaa-store-to-load.ll       | 17 +++++++++++++++++

 4 files changed, 27 insertions(+), 4 deletions(-)

 create mode 100644 test/Transforms/InstCombine/tbaa-store-to-load.ll

diff --git a/include/llvm/Analysis/Loads.h b/include/llvm/Analysis/Loads.h

index e5bd0c8..9d24b7b 100644

--- 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

index dce243c..7d3fd59 100644

--- 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

index 6a5d5a6..d312983 100644

--- a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

+++ b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

@@ -800,10 +800,12 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {

   // separated by a few arithmetic operations.

   BasicBlock::iterator BBI(LI);

   AAMDNodes AATags;

+  bool IsLoadCSE = false;

   if (Value *AvailableVal =

       FindAvailableLoadedValue(Op, 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

new file mode 100644

index 0000000..707be73

--- /dev/null

+++ 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"}