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[AMDGPU] Prefer s_memtime for readcyclecounter on GFX10 #80211

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Merged
merged 1 commit into from
Feb 1, 2024
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[AMDGPU] Prefer s_memtime for readcyclecounter on GFX10 #80211

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2 changes: 0 additions & 2 deletions llvm/lib/Target/AMDGPU/SMInstructions.td
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Original file line number Diff line number Diff line change
Expand Up @@ -1065,8 +1065,6 @@ def : GCNPat <
(REG_SEQUENCE SReg_64,
(S_GETREG_B32 getHwRegImm<HWREG.SHADER_CYCLES, 0, -12>.ret), sub0,
(S_MOV_B32 (i32 0)), sub1)> {
// Prefer this to s_memtime because it has lower and more predictable latency.
let AddedComplexity = 1;
Comment on lines -1068 to -1069
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Is the whole pattern just dead now? I would expect to need either an extra predicate for is-useful or modify the HasShaderCyclesRegister predicate

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I'm not intimately familiar with the backend. My understanding is that the added complexity ensures SelectionDAG will choose this lowering instead of the s_memtime one in cases where both are available. The only platform where both are available is gfx10 AFAIK, so removing this makes it work on gfx10. Would we need some more specific predicates? My assumption was that no new cards would have s_memtime and the shader counter at the same time.

}
} // let OtherPredicates = [HasShaderCyclesRegister]

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4 changes: 2 additions & 2 deletions llvm/test/CodeGen/AMDGPU/readcyclecounter.ll
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Expand Up @@ -4,8 +4,8 @@
; RUN: llc -global-isel=1 -mtriple=amdgcn -mcpu=tonga -verify-machineinstrs < %s | FileCheck -check-prefix=MEMTIME -check-prefix=SIVI -check-prefix=GCN %s
; RUN: llc -global-isel=0 -mtriple=amdgcn -mcpu=gfx1010 -verify-machineinstrs < %s | FileCheck -check-prefix=MEMTIME -check-prefix=GCN %s
; RUN: llc -global-isel=1 -mtriple=amdgcn -mcpu=gfx1010 -verify-machineinstrs < %s | FileCheck -check-prefix=MEMTIME -check-prefix=GCN %s
; RUN: llc -global-isel=0 -mtriple=amdgcn -mcpu=gfx1030 -verify-machineinstrs < %s | FileCheck -check-prefixes=GETREG,GETREG-SDAG -check-prefix=GCN %s
; RUN: llc -global-isel=1 -mtriple=amdgcn -mcpu=gfx1030 -verify-machineinstrs < %s | FileCheck -check-prefixes=GETREG,GETREG-GISEL -check-prefix=GCN %s
; RUN: llc -global-isel=0 -mtriple=amdgcn -mcpu=gfx1030 -verify-machineinstrs < %s | FileCheck -check-prefixes=MEMTIME -check-prefix=GCN %s
; RUN: llc -global-isel=1 -mtriple=amdgcn -mcpu=gfx1030 -verify-machineinstrs < %s | FileCheck -check-prefixes=MEMTIME -check-prefix=GCN %s
; RUN: llc -global-isel=0 -mtriple=amdgcn -mcpu=gfx1100 -verify-machineinstrs -amdgpu-enable-vopd=0 < %s | FileCheck -check-prefixes=GETREG,GETREG-SDAG -check-prefix=GCN %s
; RUN: llc -global-isel=1 -mtriple=amdgcn -mcpu=gfx1100 -verify-machineinstrs -amdgpu-enable-vopd=0 < %s | FileCheck -check-prefixes=GETREG,GETREG-GISEL -check-prefix=GCN %s
; RUN: llc -global-isel=0 -mtriple=amdgcn -mcpu=gfx1200 -verify-machineinstrs < %s | FileCheck -check-prefixes=GCN,GFX12 %s
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