[PATCH] D128123: [SDAG] try to replace subtract-from-constant with xor

Mon Jun 20 03:33:49 PDT 2022

spatel planned changes to this revision.
spatel added inline comments.

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Comment at: llvm/test/CodeGen/AMDGPU/ds-sub-offset.ll:132
+; GFX10-NEXT:    ds_write_b8 v0, v1
 ; GFX10-NEXT:    s_endpgm
   %x.i = call i32 @llvm.amdgcn.workitem.id.x() #0
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RKSimon wrote:
> RKSimon wrote:
> > Based off @foad's comments on D128080 - we need to either add a TLI override to control this or add a way for AMDGPU to reverse it.
> Hmm - how similar is TargetLowering::preferIncOfAddToSubOfNot ?
At first glance, that seems more about constant materialization while this is about a "sub-from" instruction with an immediate operand. 

That hook is default true but overridden to false for vector types by ARM/AArch/PowerPC.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D128123/new/

https://reviews.llvm.org/D128123