[PATCH] D137542: [AMDGPU] Use aperture registers instead of S_GETREG

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp:149-150
+  // register with a reference to its artificial HI 32 bits.
+  if (IsApertureRegister64(SrcReg))
+    return RBI.constrainGenericRegister(DstReg, AMDGPU::SGPR_64RegClass, *MRI);
+
----------------
Pierre-vh wrote:
> arsenm wrote:
> > You shouldn't need to special case this (also note there's no equivalent for the DAG). Either it needs to belong to a different class from SReg_64, or you need to reserve the high bits 
> > or you need to reserve the high bits
> Aren't they reserved with `reserveRegisterTuples`?
> 
> If I create a different class, do you mean I should exclude those aperture registers from SReg and create a superclass with both SReg and the apertures? I'm not sure I understand how the class will help if I shouldn't special-case the uses of those aperture registers
If the reserve didn't do it, then yes. Using different classes is the correct way to represent use restrictions. Really what we want is a class without the sub1 subregister, but has a hack we're trying to avoid that, so a class that excludes the aperture regs is the next best thing.

Not sure if you really need the reserve after that.


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  https://reviews.llvm.org/D137542/new/

https://reviews.llvm.org/D137542