fix PR9215, preventing -reassociate from clearing nsw/nuw when

it swaps the LHS/RHS of a single binop.

llvm-svn: 125700

2 files changed, 11 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index 5df6f3725a3..e093b52571a 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -348,9 +348,10 @@ void Reassociate::RewriteExprTree(BinaryOperator *I,
       I->setOperand(0, Ops[i].Op);
       I->setOperand(1, Ops[i+1].Op);
 
-      // Conservatively clear all the optional flags, which may not hold
-      // after the reassociation.
-      I->clearSubclassOptionalData();
+      // Clear all the optional flags, which may not hold after the
+      // reassociation if the expression involved more than just this operation.
+      if (Ops.size() != 2)
+        I->clearSubclassOptionalData();
 
       DEBUG(dbgs() << "TO: " << *I << '\n');
       MadeChange = true;
diff --git a/llvm/test/Transforms/Reassociate/optional-flags.ll b/llvm/test/Transforms/Reassociate/optional-flags.ll
index 5ecc7675f8e..40f7d5bf5b8 100644
--- a/llvm/test/Transforms/Reassociate/optional-flags.ll
+++ b/llvm/test/Transforms/Reassociate/optional-flags.ll
@@ -20,3 +20,10 @@ define i64 @test1(i64 %a, i64 %b, i64 %c) {
   %z = add nsw i64 %y, %a
   ret i64 %z
 }
+
+; PR9215
+; CHECK: %s = add nsw i32 %y, %x
+define i32 @test2(i32 %x, i32 %y) {
+  %s = add nsw i32 %x, %y
+  ret i32 %s
+}