[SimplifyCFG] Don't fold conditional branches that contain calls to convergent functions.

Summary:
Performing this optimization duplicates the call to the convergent
function and adds new control-flow dependencies, which is a no-no.

Reviewers: jingyue

Subscribers: broune, hfinkel, tra, resistor, joker.eph, arsenm, llvm-commits, mzolotukhin

Differential Revision: http://reviews.llvm.org/D17128

llvm-svn: 260730

1 files changed, 28 insertions, 0 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/attr-convergent.ll b/llvm/test/Transforms/SimplifyCFG/attr-convergent.ll
new file mode 100644
index 00000000000..a5f363d055a
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/attr-convergent.ll
@@ -0,0 +1,28 @@
+; RUN: opt < %s -simplifycfg -S | FileCheck %s
+
+; Checks that the SimplifyCFG pass won't duplicate a call to a function marked
+; convergent.
+;
+; CHECK: call void @barrier
+; CHECK-NOT: call void @barrier
+define void @check(i1 %cond, i32* %out) {
+entry:
+  br i1 %cond, label %if.then, label %if.end
+
+if.then:
+  store i32 5, i32* %out
+  br label %if.end
+
+if.end:
+  %x = phi i1 [ true, %entry ], [ false, %if.then ]
+  call void @barrier()
+  br i1 %x, label %cond.end, label %cond.false
+
+cond.false:
+  br label %cond.end
+
+cond.end:
+  ret void
+}
+
+declare void @barrier() convergent