[PATCH] D128582: Enable SeparateConstOffsetFromGEPPass() at -O3 and -O2

[Dave Green via Phabricator via llvm-commits]

dmgreen added a comment.

> Passing `-aarch64-enable-gep-opt=true -O3` would do the job - https://clang.godbolt.org/z/hcjsh1vex what this patch was proposing. WDYT?
>
> ..
>
> Sure. For #50528, enabling `EnableGEPOpt` reduces GEP instructions by half but is done by splitting GEP into ptr2int and int2ptr.

Oh yeah I see it does. I must have missed the -O3 off the time I tried it. That's good. I wonder why it was never enabled in the past.

>From the look of it, it runs after LSR, which I think it would need to run before. Otherwise it is likely to mess up what LSR has tried to do. That would be before the call to TargetPassConfig::addIRPasses(). I'm not sure if the LICM run is necessary either, but I see it is used in other backends. We would need to gather some benchmark to see how it behaves. Like do the issues in x264 still occur, and what happens across more benchmark cases.


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