[AMDGPU] Fix missing S_WAIT_XCNT with multiple pending VMEMs #166779
Merged
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Using different offsets for the two global loads just makes it more obvious that the second one could fail address translation even if the first one succeeds.
This is just stylistic. It allows using the identical condition in the SMEM and VMEM cases and potentially guards against more X_CNT event types being added in future.
Member
|
@llvm/pr-subscribers-backend-amdgpu Author: Jay Foad (jayfoad) ChangesFull diff: https://github.com/llvm/llvm-project/pull/166779.diff 2 Files Affected:
diff --git a/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp b/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
index b7fa899678ec7..306d59d0867cd 100644
--- a/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
@@ -1291,21 +1291,15 @@ void WaitcntBrackets::applyXcnt(const AMDGPU::Waitcnt &Wait) {
// On entry to a block with multiple predescessors, there may
// be pending SMEM and VMEM events active at the same time.
// In such cases, only clear one active event at a time.
- auto applyPendingXcntGroup = [this](unsigned E) {
- unsigned LowerBound = getScoreLB(X_CNT);
- applyWaitcnt(X_CNT, 0);
- PendingEvents |= (1 << E);
- setScoreLB(X_CNT, LowerBound);
- };
// Wait on XCNT is redundant if we are already waiting for a load to complete.
// SMEM can return out of order, so only omit XCNT wait if we are waiting till
// zero.
if (Wait.KmCnt == 0 && hasPendingEvent(SMEM_GROUP)) {
- if (hasPendingEvent(VMEM_GROUP))
- applyPendingXcntGroup(VMEM_GROUP);
- else
+ if (!hasMixedPendingEvents(X_CNT))
applyWaitcnt(X_CNT, 0);
+ else
+ PendingEvents &= ~(1 << SMEM_GROUP);
return;
}
@@ -1314,10 +1308,10 @@ void WaitcntBrackets::applyXcnt(const AMDGPU::Waitcnt &Wait) {
// decremented to the same number as LOADCnt.
if (Wait.LoadCnt != ~0u && hasPendingEvent(VMEM_GROUP) &&
!hasPendingEvent(STORE_CNT)) {
- if (hasPendingEvent(SMEM_GROUP))
- applyPendingXcntGroup(SMEM_GROUP);
- else
+ if (!hasMixedPendingEvents(X_CNT))
applyWaitcnt(X_CNT, std::min(Wait.XCnt, Wait.LoadCnt));
+ else if (Wait.LoadCnt == 0)
+ PendingEvents &= ~(1 << VMEM_GROUP);
return;
}
diff --git a/llvm/test/CodeGen/AMDGPU/wait-xcnt.mir b/llvm/test/CodeGen/AMDGPU/wait-xcnt.mir
index f964480dcc633..fe16f0d44dd1c 100644
--- a/llvm/test/CodeGen/AMDGPU/wait-xcnt.mir
+++ b/llvm/test/CodeGen/AMDGPU/wait-xcnt.mir
@@ -1069,7 +1069,6 @@ body: |
$sgpr0 = S_MOV_B32 $sgpr0
...
-# FIXME: Missing S_WAIT_XCNT before overwriting vgpr0.
---
name: mixed_pending_events
tracksRegLiveness: true
@@ -1088,8 +1087,8 @@ body: |
; GCN-NEXT: successors: %bb.2(0x80000000)
; GCN-NEXT: liveins: $vgpr0_vgpr1, $sgpr2
; GCN-NEXT: {{ $}}
- ; GCN-NEXT: $vgpr2 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 0, 0, implicit $exec
- ; GCN-NEXT: $vgpr3 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 0, 0, implicit $exec
+ ; GCN-NEXT: $vgpr2 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 100, 0, implicit $exec
+ ; GCN-NEXT: $vgpr3 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 200, 0, implicit $exec
; GCN-NEXT: {{ $}}
; GCN-NEXT: bb.2:
; GCN-NEXT: liveins: $sgpr2, $vgpr2
@@ -1098,6 +1097,7 @@ body: |
; GCN-NEXT: $vgpr2 = V_MOV_B32_e32 $vgpr2, implicit $exec
; GCN-NEXT: S_WAIT_KMCNT 0
; GCN-NEXT: $sgpr2 = S_MOV_B32 $sgpr2
+ ; GCN-NEXT: S_WAIT_XCNT 0
; GCN-NEXT: $vgpr0 = V_MOV_B32_e32 0, implicit $exec
bb.0:
liveins: $vgpr0_vgpr1, $sgpr0_sgpr1, $scc
@@ -1105,8 +1105,8 @@ body: |
S_CBRANCH_SCC1 %bb.2, implicit $scc
bb.1:
liveins: $vgpr0_vgpr1, $sgpr2
- $vgpr2 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 0, 0, implicit $exec
- $vgpr3 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 0, 0, implicit $exec
+ $vgpr2 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 100, 0, implicit $exec
+ $vgpr3 = GLOBAL_LOAD_DWORD $vgpr0_vgpr1, 200, 0, implicit $exec
bb.2:
liveins: $sgpr2, $vgpr2
$vgpr2 = V_MOV_B32_e32 $vgpr2, implicit $exec
|
Contributor
Author
|
@RyanRio FYI |
Contributor
Author
|
Split into multiple commits for ease of review and to make the final bug-fixing commit as small as possible. |
Contributor
Author
|
Eager ping - I tried hard to make this easy to review. The topmost commit should be an obvious bug fix, only clear pending VMEM events if LoadCnt == 0. The other commits are all NFC refactorings leading up to the fix. |
nhaehnle
approved these changes
Nov 11, 2025
Collaborator
nhaehnle
left a comment
nhaehnle
left a comment
There was a problem hiding this comment.
Seems reasonable to me.
cdevadas
approved these changes
Nov 12, 2025
Collaborator
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/190/builds/30802 Here is the relevant piece of the build log for the reference |
git-crd
pushed a commit
to git-crd/crd-llvm-project
that referenced
this pull request
Nov 13, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
5 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
No description provided.