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[LV] Fix branch weights in epilogue min iteration check block #152534

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Aug 11, 2025
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[LV] Fix branch weights in epilogue min iteration check block #152534

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a2bfddb
[LV] Fix branch weights in epilogue min iteration check block
david-arm Aug 7, 2025
ea9d2f9
Address review comments
david-arm Aug 8, 2025
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31 changes: 16 additions & 15 deletions llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -690,10 +690,12 @@ class InnerLoopAndEpilogueVectorizer : public InnerLoopVectorizer {
const TargetTransformInfo *TTI, AssumptionCache *AC,
OptimizationRemarkEmitter *ORE, EpilogueLoopVectorizationInfo &EPI,
LoopVectorizationCostModel *CM, BlockFrequencyInfo *BFI,
ProfileSummaryInfo *PSI, GeneratedRTChecks &Checks, VPlan &Plan)
: InnerLoopVectorizer(OrigLoop, PSE, LI, DT, TLI, TTI, AC, ORE,
EPI.MainLoopVF, EPI.MainLoopVF, EPI.MainLoopUF, CM,
BFI, PSI, Checks, Plan),
ProfileSummaryInfo *PSI, GeneratedRTChecks &Checks, VPlan &Plan,
ElementCount VecWidth, ElementCount MinProfitableTripCount,
unsigned UnrollFactor)
: InnerLoopVectorizer(OrigLoop, PSE, LI, DT, TLI, TTI, AC, ORE, VecWidth,
MinProfitableTripCount, UnrollFactor, CM, BFI, PSI,
Checks, Plan),
EPI(EPI) {}

// Override this function to handle the more complex control flow around the
Expand Down Expand Up @@ -728,8 +730,9 @@ class EpilogueVectorizerMainLoop : public InnerLoopAndEpilogueVectorizer {
OptimizationRemarkEmitter *ORE, EpilogueLoopVectorizationInfo &EPI,
LoopVectorizationCostModel *CM, BlockFrequencyInfo *BFI,
ProfileSummaryInfo *PSI, GeneratedRTChecks &Check, VPlan &Plan)
: InnerLoopAndEpilogueVectorizer(OrigLoop, PSE, LI, DT, TLI, TTI, AC, ORE,
EPI, CM, BFI, PSI, Check, Plan) {}
: InnerLoopAndEpilogueVectorizer(
OrigLoop, PSE, LI, DT, TLI, TTI, AC, ORE, EPI, CM, BFI, PSI, Check,
Plan, EPI.MainLoopVF, EPI.MainLoopVF, EPI.MainLoopUF) {}
/// Implements the interface for creating a vectorized skeleton using the
/// *main loop* strategy (ie the first pass of vplan execution).
BasicBlock *createEpilogueVectorizedLoopSkeleton() final;
Expand All @@ -755,8 +758,9 @@ class EpilogueVectorizerEpilogueLoop : public InnerLoopAndEpilogueVectorizer {
OptimizationRemarkEmitter *ORE, EpilogueLoopVectorizationInfo &EPI,
LoopVectorizationCostModel *CM, BlockFrequencyInfo *BFI,
ProfileSummaryInfo *PSI, GeneratedRTChecks &Checks, VPlan &Plan)
: InnerLoopAndEpilogueVectorizer(OrigLoop, PSE, LI, DT, TLI, TTI, AC, ORE,
EPI, CM, BFI, PSI, Checks, Plan) {
: InnerLoopAndEpilogueVectorizer(
OrigLoop, PSE, LI, DT, TLI, TTI, AC, ORE, EPI, CM, BFI, PSI, Checks,
Plan, EPI.EpilogueVF, EPI.EpilogueVF, EPI.EpilogueUF) {
TripCount = EPI.TripCount;
}
/// Implements the interface for creating a vectorized skeleton using the
Expand Down Expand Up @@ -7557,8 +7561,9 @@ EpilogueVectorizerMainLoop::emitIterationCountCheck(BasicBlock *Bypass,
assert(Bypass && "Expected valid bypass basic block.");
Value *Count = getTripCount();
MinProfitableTripCount = ElementCount::getFixed(0);
Value *CheckMinIters = createIterationCountCheck(
ForEpilogue ? EPI.EpilogueVF : VF, ForEpilogue ? EPI.EpilogueUF : UF);
Value *CheckMinIters =
createIterationCountCheck(ForEpilogue ? EPI.EpilogueVF : EPI.MainLoopVF,
ForEpilogue ? EPI.EpilogueUF : EPI.MainLoopUF);

BasicBlock *const TCCheckBlock = LoopVectorPreHeader;
if (!ForEpilogue)
Expand Down Expand Up @@ -7690,9 +7695,7 @@ EpilogueVectorizerEpilogueLoop::emitMinimumVectorEpilogueIterCountCheck(
BranchInst &BI =
*BranchInst::Create(Bypass, LoopVectorPreHeader, CheckMinIters);
if (hasBranchWeightMD(*OrigLoop->getLoopLatch()->getTerminator())) {
// FIXME: See test Transforms/LoopVectorize/branch-weights.ll. I don't
// think the MainLoopStep is correct.
unsigned MainLoopStep = UF * VF.getKnownMinValue();
unsigned MainLoopStep = EPI.MainLoopUF * EPI.MainLoopVF.getKnownMinValue();
unsigned EpilogueLoopStep =
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can you either update this to use VF/UF, or perhapos better update EpilogueVectorizerMainLoop::emitIterationCountCheck to not use VF/UF but EPI.MainLoopVF. for consistency?

EPI.EpilogueUF * EPI.EpilogueVF.getKnownMinValue();
// We assume the remaining `Count` is equally distributed in
Expand Down Expand Up @@ -10339,8 +10342,6 @@ bool LoopVectorizePass::processLoop(Loop *L) {

// Second pass vectorizes the epilogue and adjusts the control flow
// edges from the first pass.
EPI.MainLoopVF = EPI.EpilogueVF;
EPI.MainLoopUF = EPI.EpilogueUF;
EpilogueVectorizerEpilogueLoop EpilogILV(L, PSE, LI, DT, TLI, TTI, AC,
ORE, EPI, &CM, BFI, PSI,
Checks, BestEpiPlan);
Expand Down
17 changes: 9 additions & 8 deletions llvm/test/Transforms/LoopVectorize/AArch64/check-prof-info.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ define void @_Z3foov(i64 %n) {
; CHECK-V1-IC1: [[VECTOR_PH]]:
; CHECK-V1-IC1: br label %[[VECTOR_BODY:.*]]
; CHECK-V1-IC1: [[VECTOR_BODY]]:
; CHECK-V1-IC1: br i1 [[TMP10:%.*]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !prof [[PROF0]], !llvm.loop [[LOOP1:![0-9]+]]
; CHECK-V1-IC1: br i1 [[TMP8:%.*]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !prof [[PROF0]], !llvm.loop [[LOOP1:![0-9]+]]
; CHECK-V1-IC1: [[MIDDLE_BLOCK]]:
; CHECK-V1-IC1: br i1 [[CMP_N:%.*]], label %[[FOR_COND_CLEANUP:.*]], label %[[SCALAR_PH]], !prof [[PROF4:![0-9]+]]
; CHECK-V1-IC1: [[SCALAR_PH]]:
Expand All @@ -34,13 +34,13 @@ define void @_Z3foov(i64 %n) {
; CHECK-V2-IC1: [[VECTOR_PH]]:
; CHECK-V2-IC1: br label %[[VECTOR_BODY:.*]]
; CHECK-V2-IC1: [[VECTOR_BODY]]:
; CHECK-V2-IC1: br i1 [[TMP4:%.*]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !prof [[PROF1:![0-9]+]], !llvm.loop [[LOOP2:![0-9]+]]
; CHECK-V2-IC1: br i1 [[TMP2:%.*]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !prof [[PROF1:![0-9]+]], !llvm.loop [[LOOP2:![0-9]+]]
; CHECK-V2-IC1: [[MIDDLE_BLOCK]]:
; CHECK-V2-IC1: br i1 [[CMP_N:%.*]], label %[[FOR_COND_CLEANUP:.*]], label %[[SCALAR_PH]], !prof [[PROF5:![0-9]+]]
; CHECK-V2-IC1: [[SCALAR_PH]]:
; CHECK-V2-IC1: br label %[[FOR_BODY:.*]]
; CHECK-V2-IC1: [[FOR_BODY]]:
; CHECK-V2-IC1: br i1 [[EXITCOND:%.*]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !prof [[PROF5:![0-9]+]], !llvm.loop [[LOOP6:![0-9]+]]
; CHECK-V2-IC1: br i1 [[EXITCOND:%.*]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !prof [[PROF6:![0-9]+]], !llvm.loop [[LOOP7:![0-9]+]]
; CHECK-V2-IC1: [[FOR_COND_CLEANUP]]:
;
; CHECK-V2-IC4-LABEL: define void @_Z3foov(
Expand All @@ -52,15 +52,15 @@ define void @_Z3foov(i64 %n) {
; CHECK-V2-IC4: [[VECTOR_PH]]:
; CHECK-V2-IC4: br label %[[VECTOR_BODY:.*]]
; CHECK-V2-IC4: [[VECTOR_BODY]]:
; CHECK-V2-IC4: br i1 [[TMP10:%.*]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !prof [[PROF1:![0-9]+]], !llvm.loop [[LOOP2:![0-9]+]]
; CHECK-V2-IC4: br i1 [[TMP8:%.*]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !prof [[PROF1:![0-9]+]], !llvm.loop [[LOOP2:![0-9]+]]
; CHECK-V2-IC4: [[MIDDLE_BLOCK]]:
; CHECK-V2-IC4: br i1 [[CMP_N:%.*]], label %[[FOR_COND_CLEANUP:.*]], label %[[VEC_EPILOG_ITER_CHECK:.*]], !prof [[PROF5:![0-9]+]]
; CHECK-V2-IC4: [[VEC_EPILOG_ITER_CHECK]]:
; CHECK-V2-IC4: br i1 [[MIN_EPILOG_ITERS_CHECK:%.*]], label %[[VEC_EPILOG_SCALAR_PH]], label %[[VEC_EPILOG_PH]], !prof [[PROF6:![0-9]+]]
; CHECK-V2-IC4: [[VEC_EPILOG_PH]]:
; CHECK-V2-IC4: br label %[[VEC_EPILOG_VECTOR_BODY:.*]]
; CHECK-V2-IC4: [[VEC_EPILOG_VECTOR_BODY]]:
; CHECK-V2-IC4: br i1 [[TMP15:%.*]], label %[[VEC_EPILOG_MIDDLE_BLOCK:.*]], label %[[VEC_EPILOG_VECTOR_BODY]], !llvm.loop [[LOOP7:![0-9]+]]
; CHECK-V2-IC4: br i1 [[TMP11:%.*]], label %[[VEC_EPILOG_MIDDLE_BLOCK:.*]], label %[[VEC_EPILOG_VECTOR_BODY]], !llvm.loop [[LOOP7:![0-9]+]]
; CHECK-V2-IC4: [[VEC_EPILOG_MIDDLE_BLOCK]]:
; CHECK-V2-IC4: br i1 [[CMP_N10:%.*]], label %[[FOR_COND_CLEANUP]], label %[[VEC_EPILOG_SCALAR_PH]], !prof [[PROF8:![0-9]+]]
; CHECK-V2-IC4: [[VEC_EPILOG_SCALAR_PH]]:
Expand Down Expand Up @@ -101,16 +101,17 @@ for.cond.cleanup: ; preds = %for.body
; CHECK-V2-IC1: [[LOOP2]] = distinct !{[[LOOP2]], [[META3:![0-9]+]], [[META4:![0-9]+]]}
; CHECK-V2-IC1: [[META3]] = !{!"llvm.loop.isvectorized", i32 1}
; CHECK-V2-IC1: [[META4]] = !{!"llvm.loop.unroll.runtime.disable"}
; CHECK-V2-IC1: [[PROF5]] = !{!"branch_weights", i32 0, i32 0}
; CHECK-V2-IC1: [[LOOP6]] = distinct !{[[LOOP6]], [[META4]], [[META3]]}
; CHECK-V2-IC1: [[PROF5]] = !{!"branch_weights", i32 1, i32 3}
; CHECK-V2-IC1: [[PROF6]] = !{!"branch_weights", i32 0, i32 0}
; CHECK-V2-IC1: [[LOOP7]] = distinct !{[[LOOP7]], [[META4]], [[META3]]}
;.
; CHECK-V2-IC4: [[PROF0]] = !{!"branch_weights", i32 1, i32 127}
; CHECK-V2-IC4: [[PROF1]] = !{!"branch_weights", i32 1, i32 63}
; CHECK-V2-IC4: [[LOOP2]] = distinct !{[[LOOP2]], [[META3:![0-9]+]], [[META4:![0-9]+]]}
; CHECK-V2-IC4: [[META3]] = !{!"llvm.loop.isvectorized", i32 1}
; CHECK-V2-IC4: [[META4]] = !{!"llvm.loop.unroll.runtime.disable"}
; CHECK-V2-IC4: [[PROF5]] = !{!"branch_weights", i32 1, i32 15}
; CHECK-V2-IC4: [[PROF6]] = !{!"branch_weights", i32 4, i32 0}
; CHECK-V2-IC4: [[PROF6]] = !{!"branch_weights", i32 4, i32 12}
; CHECK-V2-IC4: [[LOOP7]] = distinct !{[[LOOP7]], [[META3]], [[META4]]}
; CHECK-V2-IC4: [[PROF8]] = !{!"branch_weights", i32 1, i32 3}
; CHECK-V2-IC4: [[PROF9]] = !{!"branch_weights", i32 0, i32 0}
Expand Down
9 changes: 1 addition & 8 deletions llvm/test/Transforms/LoopVectorize/branch-weights.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -4,13 +4,6 @@
; RUN: opt < %s -S -passes=loop-vectorize -force-vector-interleave=2 -force-vector-width=4 -enable-epilogue-vectorization \
; RUN: -epilogue-vectorization-force-VF=4 | FileCheck %s --check-prefix=MAINVF4IC2_EPI4

; FIXME: For MAINVF4IC2_EPI4 the branch weights in the terminator of
; the VEC_EPILOG_ITER_CHECK block should be [4,4] since we process 8
; scalar iterations in the main loop, leaving the remaining count to
; be in the range [0,7]. That gives a 4:4 chance of skipping the
; vector epilogue. I believe the problem lies in
; EpilogueVectorizerEpilogueLoop::emitMinimumVectorEpilogueIterCountCheck
; where the main loop VF is set to the same value as the epilogue VF.
define void @f0(i8 %n, i32 %len, ptr %p) !prof !0 {
; MAINVF4IC1_EPI4-LABEL: define void @f0(
; MAINVF4IC1_EPI4-SAME: i8 [[N:%.*]], i32 [[LEN:%.*]], ptr [[P:%.*]]) !prof [[PROF0:![0-9]+]] {
Expand Down Expand Up @@ -145,7 +138,7 @@ exit:
; MAINVF4IC2_EPI4: [[META5]] = !{!"llvm.loop.isvectorized", i32 1}
; MAINVF4IC2_EPI4: [[META6]] = !{!"llvm.loop.unroll.runtime.disable"}
; MAINVF4IC2_EPI4: [[PROF7]] = !{!"branch_weights", i32 1, i32 7}
; MAINVF4IC2_EPI4: [[PROF8]] = !{!"branch_weights", i32 4, i32 0}
; MAINVF4IC2_EPI4: [[PROF8]] = !{!"branch_weights", i32 4, i32 4}
; MAINVF4IC2_EPI4: [[PROF9]] = !{!"branch_weights", i32 0, i32 0}
; MAINVF4IC2_EPI4: [[LOOP10]] = distinct !{[[LOOP10]], [[META5]], [[META6]]}
; MAINVF4IC2_EPI4: [[PROF11]] = !{!"branch_weights", i32 1, i32 3}
Expand Down