AMDGPU: mark atomic instructions as sources of divergence

Summary:
As explained by the comment, threads will typically see different values
returned by atomic instructions even if the arguments are equal.

Reviewers: arsenm, tstellarAMD

Subscribers: arsenm, llvm-commits

Differential Revision: http://reviews.llvm.org/D18156

llvm-svn: 263719

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/test/Analysis/DivergenceAnalysis/AMDGPU/atomics.ll b/llvm/test/Analysis/DivergenceAnalysis/AMDGPU/atomics.ll
new file mode 100644
index 00000000000..60d0de6035b
--- /dev/null
+++ b/llvm/test/Analysis/DivergenceAnalysis/AMDGPU/atomics.ll
@@ -0,0 +1,15 @@
+; RUN: opt -mtriple=amdgcn-- -analyze -divergence %s | FileCheck %s
+
+; CHECK: DIVERGENT: %orig = atomicrmw xchg i32* %ptr, i32 %val seq_cst
+define i32 @test1(i32* %ptr, i32 %val) #0 {
+  %orig = atomicrmw xchg i32* %ptr, i32 %val seq_cst
+  ret i32 %orig
+}
+
+; CHECK: DIVERGENT: %orig = cmpxchg i32* %ptr, i32 %cmp, i32 %new seq_cst seq_cst
+define {i32, i1} @test2(i32* %ptr, i32 %cmp, i32 %new) {
+  %orig = cmpxchg i32* %ptr, i32 %cmp, i32 %new seq_cst seq_cst
+  ret {i32, i1} %orig
+}
+
+attributes #0 = { "ShaderType"="0" }