[PATCH] D93946: [FuncAttrs] Infer noreturn

Tue Jan 12 10:02:42 PST 2021

jdoerfert added a comment.

In D93946#2493440 <https://reviews.llvm.org/D93946#2493440>, @aeubanks wrote:

> In D93946#2492918 <https://reviews.llvm.org/D93946#2492918>, @sanwou01 wrote:
>
>> Hi folks, I'm afraid an 8% regression in h264ref (SPEC INT 2006) bisects to this patch. This in on AArch64 with -flto on a Neoverse-N1 based system, but I wouldn't be surprised if this showed up elsewhere too.
>>
>> How do people feel about reverting the patch while we investigate the regression? To start with, I'll try to find out why this has caused the drop in performance: it doesn't seem immediately obvious to me.
>
> I really can't see this change causing performance regressions. It only infers more precise function attributes. Could you do some initial investigation or come up with a repro? Maybe an optimization remark that doesn't fire after this change?

FWIW, I have seen similar things in the past. Better information leads to regressions because of heuristics firing later on. The "bug" is somewhere else and only exposed.

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https://reviews.llvm.org/D93946