[PATCH] D138899: [DAGCombiner] handle more store value forwarding

[Phoebe Wang via Phabricator via llvm-commits]

pengfei added a comment.

In D138899#4125143 <https://reviews.llvm.org/D138899#4125143>, @shchenz wrote:

> To me, this patch is innocent for the failure https://bugs.chromium.org/p/chromium/issues/detail?id=1412740. The patch exposes an issue in the pre-ra machine scheduler on X86 target.
>
> Before the  machine scheduler:
>
>   176B      %12:gr32 = LEA32r %fixed-stack.0, 1, $noreg, 0, $noreg
>   192B      %6:gr32 = MOV32rm %12:gr32, 1, $noreg, 0, $noreg :: (dereferenceable load (s32) from %ir.4, align 16)     // the content will be stored to 16($esp) is loaded before the filing 0 MOVUPSmr
>   208B      MOVUPSmr %18:gr32, 1, $noreg, 0, $noreg, %3:vr128 :: (store (s128) into %ir.1, align 4)
>   320B      MOV32mr $esp, 1, $noreg, 16, $noreg, %6:gr32 :: (store (s32))
>
> After the machine scheduler:
>
>   264B      %12:gr32 = LEA32r %fixed-stack.0, 1, $noreg, 0, $noreg
>   272B      MOVUPSmr %18:gr32, 1, $noreg, 0, $noreg, %3:vr128 :: (store (s128) into %ir.1, align 4)
>   280B      %6:gr32 = MOV32rm %12:gr32, 1, $noreg, 0, $noreg :: (dereferenceable load (s32) from %ir.4, align 16)      // now the content is loaded after the filling 0 MOVUPSmr
>   320B      MOV32mr $esp, 1, $noreg, 16, $noreg, %6:gr32 :: (store (s32))
>
> Seems like scheduler does not know `%6:gr32 = MOV32rm` and `MOVUPSmr` are aliased.
>
> @aeubanks Thanks for the quick action. Could you please help to verify if llc option `-enable-misched=false` can solve your issue? I am not very familiar with X86 target, do you have any suggestions about how to fix this X86 scheduling issue, create a github issue for X86 target? Thank you!

I'm not familiar with scheduler, but it looks to me like a general scheduler problem rather than X86 specific. I have filed 60744 <https://github.com/llvm/llvm-project/issues/60744>.
BTW, I found the problem cannot be reproduced without this patch. I guess it's the change happen to trigger the schedule.


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