[AMDGPU] comgr: rewrite s_sethalt to s_nop for GFX1250 A0#3087
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Rewrites every s_sethalt to s_nop 0 in-place (4-byte overwrite, no length change, no offset shifts). Defensive: LLVM almost never emits s_sethalt in production code (only via the int_amdgcn_s_sethalt intrinsic, mostly in debug builds), so this pass is dormant on most inputs -- it exists for defense-in-depth against any input ELF, compiler-emitted or hand-written, that ships s_sethalt. The replacement bytes come from LS.SNopBytes (pre-encoded at initLLVM() time, the same source the splitter uses for trampoline padding). Wired into b0a0.cpp dispatcher AFTER applyVop3pxWrapPatch (the order doesn't matter functionally -- sethalt-fix and the wrap pass don't interact -- but keeping all the A0-only post-loop passes adjacent makes the dispatch order easy to read). LIT test (hotswap-sethalt-fix.s): 4 cases -- bare s_sethalt is neutralized, s_sethalt before VOP3PX2 is neutralized, multiple s_sethalt instances are all neutralized, kernels without s_sethalt are not modified.
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Summary
This PR splits out the
s_sethalthotswap fix from #2519 into its own branch/PR.For the GFX1250 B0-to-A0 hotswap path, COMGR now detects in-shader
s_sethaltinstructions and rewrites them in-place tos_nop 0. This avoids the A0 LD_SCALE/WMMA clause-break hazard caused by a shader halt immediately before scale/WMMA execution.Details
comgr-hotswap-patch-sethalt-fix.cpps_sethaltinstructionsLS.SNopBytesreplacement bytes.textoffset for each neutralized instructionThis only handles in-code-object
s_sethalt. External halt mechanisms such as host/debugger SQ halt commands are outside COMGR’s code-object rewrite path and are not handled here.Tests
Added
hotswap-sethalt-fix.s, covering:s_sethaltrewrites_sethaltimmediately before a VOP3PX2 instructions_sethaltinstructions in one kernels_sethaltValidation run locally: