Fix a crash in which a multiplication was being reported as being both negative

and positive: positive, because it could be directly computed to be positive;
negative, because the nsw flags means it is either negative or undefined (the
multiplication always overflowed).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145104 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 17 insertions, 0 deletions

diff --git a/test/Transforms/InstSimplify/2011-11-23-MaskedBitsCrash.ll b/test/Transforms/InstSimplify/2011-11-23-MaskedBitsCrash.ll
new file mode 100644
index 0000000..6166536
--- /dev/null
+++ b/test/Transforms/InstSimplify/2011-11-23-MaskedBitsCrash.ll
@@ -0,0 +1,17 @@
+; RUN: opt < %s -instsimplify
+
+; The mul can be proved to always overflow (turning a negative value
+; into a positive one) and thus results in undefined behaviour.  At
+; the same time we were deducing from the nsw flag that that mul could
+; be assumed to have a negative value (since if not it has an undefined
+; value, which can be taken to be negative).  We were reporting the mul
+; as being both positive and negative, firing an assertion!
+define i1 @test1(i32 %a) {
+entry:
+  %0 = or i32 %a, 1
+  %1 = shl i32 %0, 31
+  %2 = mul nsw i32 %1, 4
+  %3 = and i32 %2, -4
+  %4 = icmp ne i32 %3, 0
+  ret i1 %4
+}