[llvm] [AMDGPU] Move architected SGPR implementation into isel (PR #79120)

[Christudasan Devadasan via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=amdgcn-amd-hsa -mcpu=gfx900 -mattr=+architected-sgprs --verify-machineinstrs < %s | FileCheck -check-prefix=GFX9-SDAG %s
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cdevadas wrote:

I don't think we have standalone tests that cover workgroup IDs so far.
Can you add a run line for gfx900 (or any arch before gfx12) without -mattr=archited-sgpr?
It makes more sense as this patch refactors the existing code that handles the workgroup IDs too.
Also, why no RUN line for gfx1200?

https://github.com/llvm/llvm-project/pull/79120