[LLVMdev] Handling of undef in the IR

[David Majnemer]

Hi Mehdi,

I think this is a simple bug in Reassociate.

It's assuming that objects which are Constant but not ConstantFP must have
a type which isn't floating point.

The code in question should be dispatching off of the type, not the
particular subclass of the Constant hierarchy.

The following patch seems to work fine and passes all the tests in the
repository:

diff --git a/lib/Transforms/Scalar/Reassociate.cpp
b/lib/Transforms/Scalar/Reassociate.cpp
index 4e02255..f618268 100644
--- a/lib/Transforms/Scalar/Reassociate.cpp
+++ b/lib/Transforms/Scalar/Reassociate.cpp
@@ -917,10 +917,12 @@ void Reassociate::RewriteExprTree(BinaryOperator *I,
 /// version of the value is returned, and BI is left pointing at the
instruction
 /// that should be processed next by the reassociation pass.
 static Value *NegateValue(Value *V, Instruction *BI) {
-  if (ConstantFP *C = dyn_cast<ConstantFP>(V))
-    return ConstantExpr::getFNeg(C);
-  if (Constant *C = dyn_cast<Constant>(V))
+  if (Constant *C = dyn_cast<Constant>(V)) {
+    if (C->getType()->isFPOrFPVectorTy()) {
+      return ConstantExpr::getFNeg(C);
+    }
     return ConstantExpr::getNeg(C);
+  }

On Wed, Jan 14, 2015 at 9:42 PM, Mehdi Amini <mehdi.amini at apple.com> wrote:

> Hi all,
>
> I have a very simple test case (thanks to bugpoint) that hit an assert in
> reassociate.
> (the assert is (C->getType()->isIntOrIntVectorTy() && "Cannot NEG a
> nonintegral value!"), function getNeg)
>
> The function is taking a Constant as argument, but the assert does not
> expect an undef. I’m not sure whose responsibility is it to handle that
> (caller?).
> Do we have to defensively assume that any Constant can be an undef
> anywhere and I should just add a check here?
>
> Thanks,
>
> Mehdi
>
> PS: IR attached for reference.
>
>
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