[LoopRotate] Don't perform loop rotation if the loop header calls a convergent function.

Summary:
Calls to convergent functions can be duplicated, but only if the
duplicates are not control-flow dependent on any additional values.
Loop rotation doesn't meet the bar.

Reviewers: jingyue

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

Differential Revision: http://reviews.llvm.org/D17127

llvm-svn: 260729

1 files changed, 31 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopRotate/convergent.ll b/llvm/test/Transforms/LoopRotate/convergent.ll
new file mode 100644
index 00000000000..c8b34fd75f0
--- /dev/null
+++ b/llvm/test/Transforms/LoopRotate/convergent.ll
@@ -0,0 +1,31 @@
+; RUN: opt -S -loop-rotate < %s | FileCheck %s
+
+@e = global i32 10
+
+declare void @f1(i32) convergent
+declare void @f2(i32)
+
+; The call to f1 in the loop header shouldn't be duplicated (meaning, loop
+; rotation shouldn't occur), because f1 is convergent.
+
+; CHECK: call void @f1
+; CHECK-NOT: call void @f1
+
+define void @test(i32 %x) {
+entry:
+  br label %loop
+
+loop:
+  %n.phi = phi i32 [ %n, %loop.fin ], [ 0, %entry ]
+  call void @f1(i32 %n.phi)
+  %cond = icmp eq i32 %n.phi, %x
+  br i1 %cond, label %exit, label %loop.fin
+
+loop.fin:
+  %n = add i32 %n.phi, 1
+  call void @f2(i32 %n)
+  br label %loop
+
+exit:
+  ret void
+}