diff options
| -rw-r--r-- | llvm/lib/Transforms/IPO/GlobalOpt.cpp | 7 | ||||
| -rw-r--r-- | llvm/test/Transforms/GlobalOpt/atomic.ll | 11 |
2 files changed, 16 insertions, 2 deletions
diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp index 2a869444d6e..ca0e5807b5f 100644 --- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp +++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp @@ -1980,7 +1980,12 @@ static bool processInternalGlobal( } if (GS.StoredType <= GlobalStatus::InitializerStored) { LLVM_DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n"); - GV->setConstant(true); + + // Don't actually mark a global constant if it's atomic because atomic loads + // are implemented by a trivial cmpxchg in some edge-cases and that usually + // requires write access to the variable even if it's not actually changed. + if (GS.Ordering == AtomicOrdering::NotAtomic) + GV->setConstant(true); // Clean up any obviously simplifiable users now. CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI); diff --git a/llvm/test/Transforms/GlobalOpt/atomic.ll b/llvm/test/Transforms/GlobalOpt/atomic.ll index 563c1fec7d2..7597e0f03ba 100644 --- a/llvm/test/Transforms/GlobalOpt/atomic.ll +++ b/llvm/test/Transforms/GlobalOpt/atomic.ll @@ -3,7 +3,7 @@ @GV1 = internal global i64 1 @GV2 = internal global i32 0 -; CHECK: @GV1 = internal unnamed_addr constant i64 1 +; CHECK: @GV1 = internal unnamed_addr global i64 1 ; CHECK: @GV2 = internal unnamed_addr global i32 0 define void @test1() { @@ -23,3 +23,12 @@ entry: %atomic-load = load atomic i32, i32* @GV2 seq_cst, align 4 ret i32 %atomic-load } + + +define i64 @test3() { +; CHECK-LABEL: @test3 +; CHECK: ret i64 1 + + %val = load atomic i64, i64* @GV1 acquire, align 8 + ret i64 %val +} |
