fix another miscompile in the llvm.sadd formation logic: it wasn't

checking to see if the high bits of the original add result were dead.
Inserting a smaller add and zexting back to that size is not good enough.

This is likely to be the fix for 8816.

llvm-svn: 122177

1 files changed, 22 insertions, 1 deletions

diff --git a/llvm/test/Transforms/InstCombine/overflow.ll b/llvm/test/Transforms/InstCombine/overflow.ll
index e54d315cd04..da20e2c983d 100644
--- a/llvm/test/Transforms/InstCombine/overflow.ll
+++ b/llvm/test/Transforms/InstCombine/overflow.ll
@@ -11,7 +11,7 @@ entry:
   %conv2 = sext i32 %b to i64
   %add = add nsw i64 %conv2, %conv
   %add.off = add i64 %add, 2147483648
-; CHECK: llvm.sadd.with.overflow
+; CHECK: llvm.sadd.with.overflow.i32
   %0 = icmp ugt i64 %add.off, 4294967295
   br i1 %0, label %if.then, label %if.end
 
@@ -53,3 +53,24 @@ if.end:
   ret i32 %conv9
 }
 
+; CHECK: test3
+; This is illegal to transform because the high bits of the original add are
+; live out.
+define i64 @test3(i32 %a, i32 %b) nounwind ssp {
+entry:
+  %conv = sext i32 %a to i64
+  %conv2 = sext i32 %b to i64
+  %add = add nsw i64 %conv2, %conv
+  %add.off = add i64 %add, 2147483648
+; CHECK-NOT: llvm.sadd.with.overflow
+  %0 = icmp ugt i64 %add.off, 4294967295
+  br i1 %0, label %if.then, label %if.end
+
+if.then:
+  %call = tail call i32 (...)* @throwAnExceptionOrWhatever() nounwind
+  br label %if.end
+
+if.end:
+  ret i64 %add
+; CHECK: ret i64
+}