2 files changed, 60 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index 116dc69b372..7e937bf954a 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -1598,11 +1598,6 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
   if (LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeAddress))
     return false;
 
-  // This code hasn't been audited for atomic, ordered, or volatile memory
-  // access.
-  if (!LI->isSimple())
-    return false;
-
   // Step 1: Find the non-local dependencies of the load.
   LoadDepVect Deps;
   MD->getNonLocalPointerDependency(LI, Deps);
@@ -1669,6 +1664,11 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
     return true;
   }
 
+  // This code hasn't been audited for atomic, ordered, or volatile memory
+  // access.
+  if (!LI->isSimple())
+    return false;
+
   // Step 4: Eliminate partial redundancy.
   if (!EnablePRE || !EnableLoadPRE)
     return false;
diff --git a/llvm/test/Transforms/GVN/atomic.ll b/llvm/test/Transforms/GVN/atomic.ll
index 4429e9bbad0..f8a70140cc3 100644
--- a/llvm/test/Transforms/GVN/atomic.ll
+++ b/llvm/test/Transforms/GVN/atomic.ll
@@ -337,3 +337,58 @@ define i64 @narrow2(i32* %P1) {
   ret i64 %res
 }
 
+; Note: The cross block FRE testing is deliberately light.  All of the tricky
+; bits of legality are shared code with the block-local FRE above.  These
+; are here only to show that we haven't obviously broken anything.
+
+; unordered atomic to unordered atomic
+define i32 @non_local_fre(i32* %P1) {
+; CHECK-LABEL: @non_local_fre(
+; CHECK: load atomic i32, i32* %P1
+; CHECK: ret i32 0
+; CHECK: ret i32 0
+  %a = load atomic i32, i32* %P1 unordered, align 4
+  %cmp = icmp eq i32 %a, 0
+  br i1 %cmp, label %early, label %next
+early:
+  ret i32 %a
+next:
+  %b = load atomic i32, i32* %P1 unordered, align 4
+  %res = sub i32 %a, %b
+  ret i32 %res
+}
+
+; unordered atomic to non-atomic
+define i32 @non_local_fre2(i32* %P1) {
+; CHECK-LABEL: @non_local_fre2(
+; CHECK: load atomic i32, i32* %P1
+; CHECK: ret i32 0
+; CHECK: ret i32 0
+  %a = load atomic i32, i32* %P1 unordered, align 4
+  %cmp = icmp eq i32 %a, 0
+  br i1 %cmp, label %early, label %next
+early:
+  ret i32 %a
+next:
+  %b = load i32, i32* %P1
+  %res = sub i32 %a, %b
+  ret i32 %res
+}
+
+; Can't forward ordered atomics.
+define i32 @non_local_fre3(i32* %P1) {
+; CHECK-LABEL: @non_local_fre3(
+; CHECK: load atomic i32, i32* %P1 acquire
+; CHECK: ret i32 0
+; CHECK: load atomic i32, i32* %P1 acquire
+; CHECK: ret i32 %res
+  %a = load atomic i32, i32* %P1 acquire, align 4
+  %cmp = icmp eq i32 %a, 0
+  br i1 %cmp, label %early, label %next
+early:
+  ret i32 %a
+next:
+  %b = load atomic i32, i32* %P1 acquire, align 4
+  %res = sub i32 %a, %b
+  ret i32 %res
+}