Re: [patch/committed] PR middle-end/65233 make walk-ssa_copies handle empty PHIs

[Richard Biener <richard.guenther@gmail.com>]

On Mon, Mar 2, 2015 at 6:34 AM, Aldy Hernandez <aldyh@redhat.com> wrote:
> As I mention in the PR...
>
> What's happening here is that the ipa_polymorphic_call_context constructor
> is calling walk_ssa_copies on a PHI node that has no arguments.  This
> happens because finalize_jump_threads eventually removes some PHI arguments
> as it's redirecting some edges, leaving a PHI with no arguments:
>
> SR.33_23 = PHI <>
>
> This should get cleaned up later, but the IPA polymorphic code gets called
> during the actual CFG clean-up, and walk_ssa_copies cannot handle an empty
> PHI.
>
> Approved by Honza.
>
> Fully tested on x86-64 Linux and verified that the patch fixes the ICE on an
> x86-64 Linux cross aarch64-linux-gnu cc1plus.
>
> Committed to mainline.

I think the real issue is that the walking code is executed via fold_stmt when
called with an API that tells you not to walk SSA use-def chains.

Richard.