[Reassociate] Better preserve NSW/NUW flags.

Part of PR12985.

Phabricator Revision: http://reviews.llvm.org/D6172

llvm-svn: 221555

1 files changed, 34 insertions, 0 deletions

diff --git a/llvm/test/Transforms/Reassociate/wrap-flags.ll b/llvm/test/Transforms/Reassociate/wrap-flags.ll
new file mode 100644
index 00000000000..7483acd02e5
--- /dev/null
+++ b/llvm/test/Transforms/Reassociate/wrap-flags.ll
@@ -0,0 +1,34 @@
+; RUN: opt < %s -reassociate -dce -S | FileCheck %s
+; PR12985
+
+; Verify the nsw flags are preserved when converting shl to mul.
+
+; CHECK-LABEL: @shl_to_mul_nsw(
+; CHECK: %mul = mul i32 %i, -2147483648
+; CHECK: %mul2 = add i32 %mul, 1
+define i32 @shl_to_mul_nsw(i32 %i) {
+entry:
+  %mul = shl nsw i32 %i, 31
+  %mul2 = add i32 %mul, 1
+  ret i32 %mul2
+}
+
+; CHECK-LABEL: @shl_to_mul_nuw(
+; CHECK: %mul = mul nuw i32 %i, 4
+; CHECK: %mul2 = add i32 %mul, 1
+define i32 @shl_to_mul_nuw(i32 %i) {
+entry:
+  %mul = shl nuw i32 %i, 2
+  %mul2 = add i32 %mul, 1
+  ret i32 %mul2
+}
+
+; CHECK-LABEL: @shl_to_mul_nuw_nsw(
+; CHECK: %mul = mul nuw nsw i32 %i, 4
+; CHECK: %mul2 = add i32 %mul, 1
+define i32 @shl_to_mul_nuw_nsw(i32 %i) {
+entry:
+  %mul = shl nuw nsw i32 %i, 2
+  %mul2 = add i32 %mul, 1
+  ret i32 %mul2
+}