[PATCH] Verify 'optnone' can run DAG combiner when appropriate

[Eric Christopher]

On Wed, Mar 25, 2015 at 5:14 PM Robinson, Paul <
Paul_Robinson at playstation.sony.com> wrote:

> "What caused you to notice not running the DAG combiner was a problem?"
>
>
>
> A fuzzer that we wrote generated some functions with 'optnone' and they
> crashed the compiler with instruction-selection failures.
>
> Being mostly vector-related, Andrea looked at them, and didn't take long
> to point the finger at DAG combine (or lack thereof!).
>
>
>
> Should I take this to imply you'd rather have one of the causes-a-crash
> functions as the test, instead of this one?
>
> Probably both, but definitely a comment going "this is currently necessary
for correct code generation due to <blah>".

-eric


> --paulr
>
>
>
> *From:* Eric Christopher [mailto:echristo at gmail.com]
> *Sent:* Wednesday, March 25, 2015 4:44 PM
> *To:* reviews+D8614+public+1ca59dfb9fe35dfd at reviews.llvm.org; Robinson,
> Paul; dblaikie at gmail.com
> *Cc:* llvm-commits at cs.uiuc.edu
> *Subject:* Re: [PATCH] Verify 'optnone' can run DAG combiner when
> appropriate
>
>
>
>
>
> On Wed, Mar 25, 2015 at 1:28 PM Eric Christopher <echristo at gmail.com>
> wrote:
>
> Inline comment.
>
>
> ================
> Comment at: test/CodeGen/X86/dag-optnone.ll:7
> @@ +6,3 @@
> +; that the combine is expected.
> +; Note, this will start failing if somebody decides that this combine
> should
> +; not occur at -O0 (because 'optnone' essentially sets -O0 for the
> function).
> ----------------
> Could you describe the problem that would occur were the dag combiner not
> run? That hasn't been clear either in this test or in your original commit
> reverting.
>
>
>
> Resending because I typoed and it's unclear I think:
>
>
>
> "What caused you to notice not running the DAG combiner was a problem?"
>
>
>
> -eric
>
>
>
> http://reviews.llvm.org/D8614
>
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