Skip to content

[AMDGPU] Tests for unnecessary S_WAIT_XCNT insertion #145688

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
jayfoad merged 2 commits into from
Jul 23, 2025
Merged

[AMDGPU] Tests for unnecessary S_WAIT_XCNT insertion #145688

Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
ab7b283
[AMDGPU] Tests for unnecessary S_WAIT_XCNT insertion
jayfoad Jun 25, 2025
d94961f
Merge remote-tracking branch 'origin/main' into test-xcnt-unnecessary
jayfoad Jul 21, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
42 changes: 42 additions & 0 deletions llvm/test/CodeGen/AMDGPU/wait-xcnt.mir
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -920,3 +920,45 @@ body: |
GLOBAL_STORE_DWORD $vgpr0_vgpr1, $vgpr3, 0, 0, implicit $exec
$vgpr2 = V_MOV_B32_e32 1, implicit $exec
...

# TODO: Unnecessary wait before overwriting vgpr0.
---
name: overwrite_vgpr_after_smem
tracksRegLiveness: true
machineFunctionInfo:
isEntryFunction: true
body: |
bb.0:
liveins: $vgpr0_vgpr1, $sgpr0_sgpr1
; GCN-LABEL: name: overwrite_vgpr_after_smem
; GCN: liveins: $vgpr0_vgpr1, $sgpr0_sgpr1
; GCN-NEXT: {{ $}}
; GCN-NEXT: $vgpr2 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 0, 0, implicit $exec
; GCN-NEXT: $sgpr2 = S_LOAD_DWORD_IMM $sgpr0_sgpr1, 0, 0
; GCN-NEXT: S_WAIT_XCNT 0
Copy link
Collaborator

@cdevadas cdevadas Jun 25, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Why is it unnecessary? Because of the S_LOAD?

Copy link
Contributor

@shiltian shiltian Jun 25, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

There is no dependence afterwards?

Copy link
Contributor Author

@jayfoad jayfoad Jun 25, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Why is it unnecessary?

Yeah, I should have explained: hardware does an implicit "S_WAIT_XCNT 0" between SMEM and VMEM instructions, so you never have outstanding address translations for both SMEM and VMEM at the same time.

; GCN-NEXT: $vgpr0 = V_MOV_B32_e32 0, implicit $exec
$vgpr2 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 0, 0, implicit $exec
$sgpr2 = S_LOAD_DWORD_IMM $sgpr0_sgpr1, 0, 0
$vgpr0 = V_MOV_B32_e32 0, implicit $exec
...

# TODO: Unnecessary wait before overwriting sgpr0.
---
name: overwrite_sgpr_after_vmem
tracksRegLiveness: true
machineFunctionInfo:
isEntryFunction: true
body: |
bb.0:
liveins: $vgpr0_vgpr1, $sgpr0_sgpr1
; GCN-LABEL: name: overwrite_sgpr_after_vmem
; GCN: liveins: $vgpr0_vgpr1, $sgpr0_sgpr1
; GCN-NEXT: {{ $}}
; GCN-NEXT: $sgpr2 = S_LOAD_DWORD_IMM $sgpr0_sgpr1, 0, 0
; GCN-NEXT: $vgpr2 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 0, 0, implicit $exec
; GCN-NEXT: S_WAIT_XCNT 0
Copy link
Collaborator

@cdevadas cdevadas Jun 25, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Again, why is it not needed?

; GCN-NEXT: $sgpr0 = S_MOV_B32 0
$sgpr2 = S_LOAD_DWORD_IMM $sgpr0_sgpr1, 0, 0
$vgpr2 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 0, 0, implicit $exec
$sgpr0 = S_MOV_B32 0
...
Loading