[PATCH] D103321: [AMDGPU] Stop mulhi from doing 24 bit mul for uniform values

Mon Jun 21 06:07:39 PDT 2021

dstuttard marked an inline comment as done.
dstuttard added inline comments.

================
Comment at: llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h:166
+  bool hasSMulHi() const {
+    return HasSMulHi;
+  }
----------------
dstuttard wrote:
> foad wrote:
> > dstuttard wrote:
> > > foad wrote:
> > > > I would just put the >= GFX9 test in here. No need for a HasSMulHi field. There are plenty of precedents for this.
> > > Having given this some thought I'm not sure that I agree - the precedent in the implementation is to do something like I've implemented. That's the consistent thing to do.
> > > Is there a good reason not to (other than it is slightly less code?) - implemented this way it is a lot clearer too.
> > Both implementations ultimately say that s_mul_hi is supported on gfx9+. Mine just has fewer moving parts. I don't find yours clearer.
> Until there's a variant at some point in the future that doesn't have SMulHi (although I guess the implementation can be changed if that ever occurs).
Actually - this is the way that this is handled in other cases. Because this test is inside AMDGPUISelLowering it has to use the SubTarget - so the test function has to be exposed from AMDGPUSubtarget - the getGeneration is only supported in GCNSubtarget (and defaults to false for the others - which is correct).

Repository:
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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D103321/new/

https://reviews.llvm.org/D103321