Since commit 157467, if reassociate isn't actually going to change an expression

then it doesn't alter the instructions composing it, however it would continue
to move the instructions to just before the expression root.  Ensure it doesn't
move them either, so now it really does nothing if there is nothing to do.  That
commit also ensured that nsw etc flags weren't cleared if the expression was not
being changed.  Tweak this a bit so that it doesn't clear flags on the initial
part of a computation either if that part didn't change but later bits did.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157518 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 38 insertions, 0 deletions

diff --git a/test/Transforms/Reassociate/no-op.ll b/test/Transforms/Reassociate/no-op.ll
new file mode 100644
index 0000000..0444cf0
--- /dev/null
+++ b/test/Transforms/Reassociate/no-op.ll
@@ -0,0 +1,38 @@
+; RUN: opt < %s -reassociate -S | FileCheck %s
+
+; When there is nothing to do, or not much to do, check that reassociate leaves
+; things alone.
+
+declare void @use(i32)
+
+define void @test1(i32 %a, i32 %b) {
+; Shouldn't change or move any of the add instructions.  Should commute but
+; otherwise not change or move any of the mul instructions.
+; CHECK: @test1
+  %a0 = add nsw i32 %a, 1
+; CHECK-NEXT: %a0 = add nsw i32 %a, 1
+  %m0 = mul nsw i32 3, %a
+; CHECK-NEXT: %m0 = mul nsw i32 %a, 3
+  %a1 = add nsw i32 %a0, %b
+; CHECK-NEXT: %a1 = add nsw i32 %a0, %b
+  %m1 = mul nsw i32 %b, %m0
+; CHECK-NEXT: %m1 = mul nsw i32 %m0, %b
+  call void @use(i32 %a1)
+; CHECK-NEXT: call void @use
+  call void @use(i32 %m1)
+  ret void
+}
+
+define void @test2(i32 %a, i32 %b, i32 %c, i32 %d) {
+; The initial add doesn't change so should not lose the nsw flag.
+; CHECK: @test2
+  %a0 = add nsw i32 %b, %a
+; CHECK-NEXT: %a0 = add nsw i32 %b, %a
+  %a1 = add nsw i32 %a0, %d
+; CHECK-NEXT: %a1 = add i32 %a0, %c
+  %a2 = add nsw i32 %a1, %c
+; CHECK-NEXT: %a2 = add i32 %a1, %d
+  call void @use(i32 %a2)
+; CHECK-NEXT: call void @use
+  ret void
+}