[llvm] 15f1cff - [MemoryDependency] Relax the re-ordering with volatile store.

[Serguei Katkov via llvm-commits]

Author: Serguei Katkov
Date: 2022-02-16T10:58:48+07:00
New Revision: 15f1cffb3afd361bf368cc7acfd6cfbfe8f77863

URL: https://github.com/llvm/llvm-project/commit/15f1cffb3afd361bf368cc7acfd6cfbfe8f77863
DIFF: https://github.com/llvm/llvm-project/commit/15f1cffb3afd361bf368cc7acfd6cfbfe8f77863.diff

LOG: [MemoryDependency] Relax the re-ordering with volatile store.

Volatile store does not provide any special rules for reordering with
atomics. Usual must alias anaylsis is enough here.

This makes the bahavior similar to how volatile load is handled.

Reviewers: reames, nikic
Reviewed By: reames
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D119818

Added: 
    

Modified: 
    llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
    llvm/test/Analysis/MemoryDependenceAnalysis/reorder-volatile.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index 36df462c7a660..a4491f481c0fb 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -556,13 +556,11 @@ MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
           return MemDepResult::getClobber(SI);
       }
 
-      // FIXME: this is overly conservative.
       // While volatile access cannot be eliminated, they do not have to clobber
       // non-aliasing locations, as normal accesses can for example be reordered
       // with volatile accesses.
       if (SI->isVolatile())
-        if (!QueryInst || isNonSimpleLoadOrStore(QueryInst) ||
-            isOtherMemAccess(QueryInst))
+        if (!QueryInst || QueryInst->isVolatile())
           return MemDepResult::getClobber(SI);
 
       // If alias analysis can tell that this store is guaranteed to not modify

diff  --git a/llvm/test/Analysis/MemoryDependenceAnalysis/reorder-volatile.ll b/llvm/test/Analysis/MemoryDependenceAnalysis/reorder-volatile.ll
index a28cb6ec8ff83..2237e685c43ef 100644
--- a/llvm/test/Analysis/MemoryDependenceAnalysis/reorder-volatile.ll
+++ b/llvm/test/Analysis/MemoryDependenceAnalysis/reorder-volatile.ll
@@ -53,11 +53,8 @@ define i32 @test_load_with_seq_cst_load() {
 
 define i32 @test_store(i32 %x) {
 ; CHECK-LABEL: @test_store(
-; CHECK-NEXT:    [[L1:%.*]] = load atomic i32, i32* @w unordered, align 4
 ; CHECK-NEXT:    store volatile i32 [[X:%.*]], i32* @u, align 4
-; CHECK-NEXT:    [[L2:%.*]] = load atomic i32, i32* @w unordered, align 4
-; CHECK-NEXT:    [[RES:%.*]] = sub i32 [[L1]], [[L2]]
-; CHECK-NEXT:    ret i32 [[RES]]
+; CHECK-NEXT:    ret i32 0
 ;
   %l1 = load atomic i32, i32* @w unordered, align 4
   store volatile i32 %x, i32* @u, align 4