Skip to content

[LVer][profcheck] explicitly set unknown branch weights for the versioned/unversioned selector #164507

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
merged 1 commit into from
Nov 5, 2025
+10 −4
Merged

[LVer][profcheck] explicitly set unknown branch weights for the versioned/unversioned selector #164507

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
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
9 changes: 7 additions & 2 deletions llvm/lib/Transforms/Utils/LoopVersioning.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@
#include "llvm/IR/Dominators.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/ProfDataUtils.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Cloning.h"
Expand Down Expand Up @@ -109,8 +110,12 @@ void LoopVersioning::versionLoop(
// Insert the conditional branch based on the result of the memchecks.
Instruction *OrigTerm = RuntimeCheckBB->getTerminator();
Builder.SetInsertPoint(OrigTerm);
Builder.CreateCondBr(RuntimeCheck, NonVersionedLoop->getLoopPreheader(),
VersionedLoop->getLoopPreheader());
auto *BI =
Builder.CreateCondBr(RuntimeCheck, NonVersionedLoop->getLoopPreheader(),
VersionedLoop->getLoopPreheader());
// We don't know what the probability of executing the versioned vs the
// unversioned variants is.
setExplicitlyUnknownBranchWeightsIfProfiled(*BI, DEBUG_TYPE);
OrigTerm->eraseFromParent();

// The loops merge in the original exit block. This is now dominated by the
Expand Down
5 changes: 3 additions & 2 deletions llvm/test/Transforms/LoopDistribute/basic-with-memchecks.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@ target triple = "x86_64-apple-macosx10.10.0"
@E = common global ptr null, align 8

; CHECK-LABEL: @f(
define void @f() {
define void @f() !prof !{!"function_entry_count", i32 10} {
entry:
%a = load ptr, ptr @A, align 8
%b = load ptr, ptr @B, align 8
Expand All @@ -55,7 +55,7 @@ entry:
; CHECK: = icmp

; CHECK-NOT: = icmp
; CHECK: br i1 %conflict.rdx15, label %for.body.ph.lver.orig, label %for.body.ph.ldist1
; CHECK: br i1 %conflict.rdx15, label %for.body.ph.lver.orig, label %for.body.ph.ldist1, !prof ![[PROF1:[0-9]]]

; The non-distributed loop that the memchecks fall back on.

Expand Down Expand Up @@ -289,3 +289,4 @@ attributes #1 = { nounwind convergent }

!0 = distinct !{!0, !1}
!1 = !{!"llvm.loop.distribute.enable", i1 true}
; CHECK: ![[PROF1]] = !{!"unknown", !"loop-versioning"}