[LLVM][LV] Improve UF calculation for vscale based scalar loops. #146102
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Update getSmallConstantTripCount() to return scalable ElementCount values that is used to acurrately determine the maximum value for UF, namely: TripCount / VF ==> X * VScale / Y * VScale ==> X / Y This improves the chances of being able to remove the scalar loop and also fixes an issue where a UF=2 is choosen for a scalar loop with exactly VF(= X * VScale) iterations.
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@llvm/pr-subscribers-llvm-transforms Author: Paul Walker (paulwalker-arm) ChangesUpdate getSmallConstantTripCount() to return scalable ElementCount values that is used to acurrately determine the maximum value for UF, namely: TripCount / VF ==> X * VScale / Y * VScale ==> X / Y This improves the chances of being able to remove the scalar loop and also fixes an issue where a UF=2 is choosen for a scalar loop with exactly VF(= X * VScale) iterations. Full diff: https://github.com/llvm/llvm-project/pull/146102.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index bb29e4fc6d232..8a4435eed95bf 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -423,7 +423,26 @@ static bool hasIrregularType(Type *Ty, const DataLayout &DL) {
/// ElementCount to include loops whose trip count is a function of vscale.
static ElementCount getSmallConstantTripCount(ScalarEvolution *SE,
const Loop *L) {
- return ElementCount::getFixed(SE->getSmallConstantTripCount(L));
+ if (unsigned ExpectedTC = SE->getSmallConstantTripCount(L))
+ return ElementCount::getFixed(ExpectedTC);
+
+ const SCEV *BTC = SE->getBackedgeTakenCount(L);
+
+ if (isa<SCEVCouldNotCompute>(BTC))
+ return ElementCount::getFixed(0);
+
+ const SCEV *ExitCount = SE->getTripCountFromExitCount(BTC, BTC->getType(), L);
+
+ if (isa<SCEVVScale>(ExitCount))
+ return ElementCount::getScalable(1);
+
+ if (auto *Mul = dyn_cast<SCEVMulExpr>(ExitCount))
+ if (Mul->getNumOperands() == 2 && isa<SCEVConstant>(Mul->getOperand(0)) &&
+ isa<SCEVVScale>(Mul->getOperand(1)))
+ return ElementCount::getScalable(
+ cast<SCEVConstant>(Mul->getOperand(0))->getValue()->getZExtValue());
+
+ return ElementCount::getFixed(0);
}
/// Returns "best known" trip count, which is either a valid positive trip count
@@ -4813,16 +4832,22 @@ LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
MaxInterleaveCount = ForceTargetMaxVectorInterleaveFactor;
}
- unsigned EstimatedVF = getEstimatedRuntimeVF(VF, VScaleForTuning);
-
// Try to get the exact trip count, or an estimate based on profiling data or
// ConstantMax from PSE, failing that.
- if (auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop)) {
+ auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop);
+
+ // For fixed length VFs treat a scalable trip count as unknown.
+ if (BestKnownTC && (BestKnownTC->isFixed() || VF.isScalable())) {
+ // Re-evaluate VF to be in the same numerical space as the trip count.
+ unsigned EstimatedVF = VF.getKnownMinValue();
+ if (VF.isScalable() && BestKnownTC->isFixed())
+ EstimatedVF = getEstimatedRuntimeVF(VF, VScaleForTuning);
+
// At least one iteration must be scalar when this constraint holds. So the
// maximum available iterations for interleaving is one less.
unsigned AvailableTC = requiresScalarEpilogue(VF.isVector())
- ? BestKnownTC->getFixedValue() - 1
- : BestKnownTC->getFixedValue();
+ ? BestKnownTC->getKnownMinValue() - 1
+ : BestKnownTC->getKnownMinValue();
unsigned InterleaveCountLB = bit_floor(std::max(
1u, std::min(AvailableTC / (EstimatedVF * 2), MaxInterleaveCount)));
diff --git a/llvm/test/Transforms/LoopVectorize/AArch64/sve-vscale-based-trip-counts.ll b/llvm/test/Transforms/LoopVectorize/AArch64/sve-vscale-based-trip-counts.ll
index e2c7469a97819..dd1606c0f349a 100644
--- a/llvm/test/Transforms/LoopVectorize/AArch64/sve-vscale-based-trip-counts.ll
+++ b/llvm/test/Transforms/LoopVectorize/AArch64/sve-vscale-based-trip-counts.ll
@@ -10,62 +10,35 @@ define void @vscale_mul_4(ptr noalias noundef readonly captures(none) %a, ptr no
; CHECK-NEXT: [[TMP0:%.*]] = tail call i64 @llvm.vscale.i64()
; CHECK-NEXT: [[TMP1:%.*]] = shl nuw nsw i64 [[TMP0]], 2
; CHECK-NEXT: [[TMP2:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP3:%.*]] = mul nuw i64 [[TMP2]], 8
-; CHECK-NEXT: [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[TMP1]], [[TMP3]]
-; CHECK-NEXT: br i1 [[MIN_ITERS_CHECK]], label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
-; CHECK: [[VECTOR_PH]]:
+; CHECK-NEXT: [[TMP3:%.*]] = mul nuw i64 [[TMP2]], 4
; CHECK-NEXT: [[TMP4:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP5:%.*]] = mul nuw i64 [[TMP4]], 8
+; CHECK-NEXT: [[TMP5:%.*]] = mul nuw i64 [[TMP4]], 4
; CHECK-NEXT: [[N_MOD_VF:%.*]] = urem i64 [[TMP1]], [[TMP5]]
; CHECK-NEXT: [[N_VEC:%.*]] = sub i64 [[TMP1]], [[N_MOD_VF]]
-; CHECK-NEXT: [[TMP10:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP7:%.*]] = mul nuw i64 [[TMP10]], 8
-; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
-; CHECK: [[VECTOR_BODY]]:
-; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-NEXT: [[TMP13:%.*]] = getelementptr inbounds nuw float, ptr [[A]], i64 [[INDEX]]
-; CHECK-NEXT: [[TMP14:%.*]] = getelementptr inbounds nuw float, ptr [[TMP13]], i32 0
-; CHECK-NEXT: [[TMP18:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP11:%.*]] = mul nuw i64 [[TMP18]], 4
-; CHECK-NEXT: [[TMP26:%.*]] = getelementptr inbounds nuw float, ptr [[TMP13]], i64 [[TMP11]]
-; CHECK-NEXT: [[WIDE_LOAD2:%.*]] = load <vscale x 4 x float>, ptr [[TMP14]], align 4
-; CHECK-NEXT: [[WIDE_LOAD1:%.*]] = load <vscale x 4 x float>, ptr [[TMP26]], align 4
-; CHECK-NEXT: [[TMP12:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i64 [[INDEX]]
-; CHECK-NEXT: [[TMP17:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i32 0
-; CHECK-NEXT: [[TMP15:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP16:%.*]] = mul nuw i64 [[TMP15]], 4
-; CHECK-NEXT: [[TMP27:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i64 [[TMP16]]
-; CHECK-NEXT: [[WIDE_LOAD3:%.*]] = load <vscale x 4 x float>, ptr [[TMP17]], align 4
-; CHECK-NEXT: [[WIDE_LOAD4:%.*]] = load <vscale x 4 x float>, ptr [[TMP27]], align 4
-; CHECK-NEXT: [[TMP19:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD2]], [[WIDE_LOAD3]]
-; CHECK-NEXT: [[TMP28:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD1]], [[WIDE_LOAD4]]
-; CHECK-NEXT: [[TMP20:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP21:%.*]] = mul nuw i64 [[TMP20]], 4
-; CHECK-NEXT: [[TMP22:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i64 [[TMP21]]
-; CHECK-NEXT: store <vscale x 4 x float> [[TMP19]], ptr [[TMP17]], align 4
-; CHECK-NEXT: store <vscale x 4 x float> [[TMP28]], ptr [[TMP22]], align 4
-; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP7]]
-; CHECK-NEXT: [[TMP23:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT: br i1 [[TMP23]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
-; CHECK: [[MIDDLE_BLOCK]]:
+; CHECK-NEXT: [[TMP6:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT: [[TMP7:%.*]] = mul nuw i64 [[TMP6]], 4
+; CHECK-NEXT: [[TMP8:%.*]] = getelementptr inbounds nuw float, ptr [[A]], i32 0
+; CHECK-NEXT: [[WIDE_LOAD:%.*]] = load <vscale x 4 x float>, ptr [[TMP8]], align 4
+; CHECK-NEXT: [[TMP9:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i32 0
+; CHECK-NEXT: [[WIDE_LOAD1:%.*]] = load <vscale x 4 x float>, ptr [[TMP9]], align 4
+; CHECK-NEXT: [[TMP10:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD]], [[WIDE_LOAD1]]
+; CHECK-NEXT: [[TMP11:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i32 0
+; CHECK-NEXT: store <vscale x 4 x float> [[TMP10]], ptr [[TMP11]], align 4
; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[TMP1]], [[N_VEC]]
-; CHECK-NEXT: br i1 [[CMP_N]], label %[[FOR_COND_CLEANUP:.*]], label %[[SCALAR_PH]]
-; CHECK: [[SCALAR_PH]]:
-; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
-; CHECK-NEXT: br label %[[FOR_BODY:.*]]
+; CHECK-NEXT: br i1 [[CMP_N]], label %[[FOR_COND_CLEANUP:.*]], label %[[FOR_BODY:.*]]
; CHECK: [[FOR_COND_CLEANUP]]:
; CHECK-NEXT: ret void
; CHECK: [[FOR_BODY]]:
-; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[INDVARS_IV_NEXT:%.*]], %[[FOR_BODY]] ]
+; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], %[[FOR_BODY]] ], [ [[N_VEC]], %[[ENTRY]] ]
; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds nuw float, ptr [[A]], i64 [[INDVARS_IV]]
-; CHECK-NEXT: [[TMP24:%.*]] = load float, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT: [[TMP12:%.*]] = load float, ptr [[ARRAYIDX]], align 4
; CHECK-NEXT: [[ARRAYIDX3:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i64 [[INDVARS_IV]]
-; CHECK-NEXT: [[TMP25:%.*]] = load float, ptr [[ARRAYIDX3]], align 4
-; CHECK-NEXT: [[MUL4:%.*]] = fmul float [[TMP24]], [[TMP25]]
+; CHECK-NEXT: [[TMP13:%.*]] = load float, ptr [[ARRAYIDX3]], align 4
+; CHECK-NEXT: [[MUL4:%.*]] = fmul float [[TMP12]], [[TMP13]]
; CHECK-NEXT: store float [[MUL4]], ptr [[ARRAYIDX3]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[TMP1]]
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
;
entry:
%0 = tail call i64 @llvm.vscale.i64()
@@ -136,7 +109,7 @@ define void @vscale_mul_8(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: store float [[MUL5]], ptr [[ARRAYIDX4]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[MUL1]]
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
+; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP3:![0-9]+]]
;
entry:
%0 = tail call i64 @llvm.vscale.i64()
@@ -166,43 +139,30 @@ define void @vscale_mul_12(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: [[TMP0:%.*]] = tail call i64 @llvm.vscale.i64()
; CHECK-NEXT: [[MUL1:%.*]] = mul nuw nsw i64 [[TMP0]], 12
; CHECK-NEXT: [[TMP1:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP2:%.*]] = mul nuw i64 [[TMP1]], 8
+; CHECK-NEXT: [[TMP2:%.*]] = mul nuw i64 [[TMP1]], 4
; CHECK-NEXT: [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[MUL1]], [[TMP2]]
; CHECK-NEXT: br i1 [[MIN_ITERS_CHECK]], label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: [[TMP3:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP4:%.*]] = mul nuw i64 [[TMP3]], 8
+; CHECK-NEXT: [[TMP4:%.*]] = mul nuw i64 [[TMP3]], 4
; CHECK-NEXT: [[N_MOD_VF:%.*]] = urem i64 [[MUL1]], [[TMP4]]
; CHECK-NEXT: [[N_VEC:%.*]] = sub i64 [[MUL1]], [[N_MOD_VF]]
; CHECK-NEXT: [[TMP5:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP6:%.*]] = mul nuw i64 [[TMP5]], 8
+; CHECK-NEXT: [[TMP6:%.*]] = mul nuw i64 [[TMP5]], 4
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[TMP7:%.*]] = getelementptr inbounds nuw float, ptr [[A]], i64 [[INDEX]]
; CHECK-NEXT: [[TMP8:%.*]] = getelementptr inbounds nuw float, ptr [[TMP7]], i32 0
-; CHECK-NEXT: [[TMP9:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP10:%.*]] = mul nuw i64 [[TMP9]], 4
-; CHECK-NEXT: [[TMP11:%.*]] = getelementptr inbounds nuw float, ptr [[TMP7]], i64 [[TMP10]]
-; CHECK-NEXT: [[WIDE_LOAD1:%.*]] = load <vscale x 4 x float>, ptr [[TMP8]], align 4
-; CHECK-NEXT: [[WIDE_LOAD2:%.*]] = load <vscale x 4 x float>, ptr [[TMP11]], align 4
-; CHECK-NEXT: [[TMP12:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i64 [[INDEX]]
-; CHECK-NEXT: [[TMP13:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i32 0
-; CHECK-NEXT: [[TMP14:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP15:%.*]] = mul nuw i64 [[TMP14]], 4
-; CHECK-NEXT: [[TMP16:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i64 [[TMP15]]
-; CHECK-NEXT: [[WIDE_LOAD3:%.*]] = load <vscale x 4 x float>, ptr [[TMP13]], align 4
-; CHECK-NEXT: [[WIDE_LOAD4:%.*]] = load <vscale x 4 x float>, ptr [[TMP16]], align 4
-; CHECK-NEXT: [[TMP18:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD1]], [[WIDE_LOAD3]]
-; CHECK-NEXT: [[TMP25:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD2]], [[WIDE_LOAD4]]
-; CHECK-NEXT: [[TMP19:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP20:%.*]] = mul nuw i64 [[TMP19]], 4
-; CHECK-NEXT: [[TMP21:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i64 [[TMP20]]
-; CHECK-NEXT: store <vscale x 4 x float> [[TMP18]], ptr [[TMP13]], align 4
-; CHECK-NEXT: store <vscale x 4 x float> [[TMP25]], ptr [[TMP21]], align 4
+; CHECK-NEXT: [[WIDE_LOAD:%.*]] = load <vscale x 4 x float>, ptr [[TMP8]], align 4
+; CHECK-NEXT: [[TMP9:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i64 [[INDEX]]
+; CHECK-NEXT: [[TMP10:%.*]] = getelementptr inbounds nuw float, ptr [[TMP9]], i32 0
+; CHECK-NEXT: [[WIDE_LOAD1:%.*]] = load <vscale x 4 x float>, ptr [[TMP10]], align 4
+; CHECK-NEXT: [[TMP11:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD]], [[WIDE_LOAD1]]
+; CHECK-NEXT: store <vscale x 4 x float> [[TMP11]], ptr [[TMP10]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP6]]
-; CHECK-NEXT: [[TMP22:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT: br i1 [[TMP22]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP5:![0-9]+]]
+; CHECK-NEXT: [[TMP12:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT: br i1 [[TMP12]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[MUL1]], [[N_VEC]]
; CHECK-NEXT: br i1 [[CMP_N]], label %[[FOR_COND_CLEANUP:.*]], label %[[SCALAR_PH]]
@@ -214,14 +174,14 @@ define void @vscale_mul_12(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK: [[FOR_BODY]]:
; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[INDVARS_IV_NEXT:%.*]], %[[FOR_BODY]] ]
; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds nuw float, ptr [[A]], i64 [[INDVARS_IV]]
-; CHECK-NEXT: [[TMP23:%.*]] = load float, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT: [[TMP13:%.*]] = load float, ptr [[ARRAYIDX]], align 4
; CHECK-NEXT: [[ARRAYIDX4:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i64 [[INDVARS_IV]]
-; CHECK-NEXT: [[TMP24:%.*]] = load float, ptr [[ARRAYIDX4]], align 4
-; CHECK-NEXT: [[MUL5:%.*]] = fmul float [[TMP23]], [[TMP24]]
+; CHECK-NEXT: [[TMP14:%.*]] = load float, ptr [[ARRAYIDX4]], align 4
+; CHECK-NEXT: [[MUL5:%.*]] = fmul float [[TMP13]], [[TMP14]]
; CHECK-NEXT: store float [[MUL5]], ptr [[ARRAYIDX4]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[MUL1]]
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
+; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP5:![0-9]+]]
;
entry:
%0 = tail call i64 @llvm.vscale.i64()
@@ -287,7 +247,7 @@ define void @vscale_mul_31(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: store <vscale x 4 x float> [[TMP18]], ptr [[TMP21]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP6]]
; CHECK-NEXT: [[TMP22:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT: br i1 [[TMP22]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP7:![0-9]+]]
+; CHECK-NEXT: br i1 [[TMP22]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[MUL1]], [[N_VEC]]
; CHECK-NEXT: br i1 [[CMP_N]], label %[[FOR_COND_CLEANUP:.*]], label %[[SCALAR_PH]]
@@ -306,7 +266,7 @@ define void @vscale_mul_31(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: store float [[MUL5]], ptr [[ARRAYIDX4]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[MUL1]]
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
+; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP7:![0-9]+]]
;
entry:
%0 = tail call i64 @llvm.vscale.i64()
@@ -372,7 +332,7 @@ define void @vscale_mul_64(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: store <vscale x 4 x float> [[TMP18]], ptr [[TMP21]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP6]]
; CHECK-NEXT: [[TMP22:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT: br i1 [[TMP22]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP9:![0-9]+]]
+; CHECK-NEXT: br i1 [[TMP22]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[MUL1]], [[N_VEC]]
; CHECK-NEXT: br i1 [[CMP_N]], label %[[FOR_COND_CLEANUP:.*]], label %[[SCALAR_PH]]
@@ -391,7 +351,7 @@ define void @vscale_mul_64(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: store float [[MUL5]], ptr [[ARRAYIDX4]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[MUL1]]
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP10:![0-9]+]]
+; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP9:![0-9]+]]
;
entry:
%0 = tail call i64 @llvm.vscale.i64()
@@ -419,14 +379,13 @@ declare i64 @llvm.vscale.i64()
attributes #0 = { vscale_range(1,16) "target-features"="+sve" }
;.
; CHECK: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]], [[META2:![0-9]+]]}
-; CHECK: [[META1]] = !{!"llvm.loop.isvectorized", i32 1}
-; CHECK: [[META2]] = !{!"llvm.loop.unroll.runtime.disable"}
-; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META2]], [[META1]]}
+; CHECK: [[META1]] = !{!"llvm.loop.unroll.runtime.disable"}
+; CHECK: [[META2]] = !{!"llvm.loop.isvectorized", i32 1}
+; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META1]], [[META2]]}
; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META2]], [[META1]]}
; CHECK: [[LOOP5]] = distinct !{[[LOOP5]], [[META1]], [[META2]]}
; CHECK: [[LOOP6]] = distinct !{[[LOOP6]], [[META2]], [[META1]]}
; CHECK: [[LOOP7]] = distinct !{[[LOOP7]], [[META1]], [[META2]]}
; CHECK: [[LOOP8]] = distinct !{[[LOOP8]], [[META2]], [[META1]]}
; CHECK: [[LOOP9]] = distinct !{[[LOOP9]], [[META1]], [[META2]]}
-; CHECK: [[LOOP10]] = distinct !{[[LOOP10]], [[META2]], [[META1]]}
;.
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@llvm/pr-subscribers-vectorizers Author: Paul Walker (paulwalker-arm) ChangesUpdate getSmallConstantTripCount() to return scalable ElementCount values that is used to acurrately determine the maximum value for UF, namely: TripCount / VF ==> X * VScale / Y * VScale ==> X / Y This improves the chances of being able to remove the scalar loop and also fixes an issue where a UF=2 is choosen for a scalar loop with exactly VF(= X * VScale) iterations. Full diff: https://github.com/llvm/llvm-project/pull/146102.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index bb29e4fc6d232..8a4435eed95bf 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -423,7 +423,26 @@ static bool hasIrregularType(Type *Ty, const DataLayout &DL) {
/// ElementCount to include loops whose trip count is a function of vscale.
static ElementCount getSmallConstantTripCount(ScalarEvolution *SE,
const Loop *L) {
- return ElementCount::getFixed(SE->getSmallConstantTripCount(L));
+ if (unsigned ExpectedTC = SE->getSmallConstantTripCount(L))
+ return ElementCount::getFixed(ExpectedTC);
+
+ const SCEV *BTC = SE->getBackedgeTakenCount(L);
+
+ if (isa<SCEVCouldNotCompute>(BTC))
+ return ElementCount::getFixed(0);
+
+ const SCEV *ExitCount = SE->getTripCountFromExitCount(BTC, BTC->getType(), L);
+
+ if (isa<SCEVVScale>(ExitCount))
+ return ElementCount::getScalable(1);
+
+ if (auto *Mul = dyn_cast<SCEVMulExpr>(ExitCount))
+ if (Mul->getNumOperands() == 2 && isa<SCEVConstant>(Mul->getOperand(0)) &&
+ isa<SCEVVScale>(Mul->getOperand(1)))
+ return ElementCount::getScalable(
+ cast<SCEVConstant>(Mul->getOperand(0))->getValue()->getZExtValue());
+
+ return ElementCount::getFixed(0);
}
/// Returns "best known" trip count, which is either a valid positive trip count
@@ -4813,16 +4832,22 @@ LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
MaxInterleaveCount = ForceTargetMaxVectorInterleaveFactor;
}
- unsigned EstimatedVF = getEstimatedRuntimeVF(VF, VScaleForTuning);
-
// Try to get the exact trip count, or an estimate based on profiling data or
// ConstantMax from PSE, failing that.
- if (auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop)) {
+ auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop);
+
+ // For fixed length VFs treat a scalable trip count as unknown.
+ if (BestKnownTC && (BestKnownTC->isFixed() || VF.isScalable())) {
+ // Re-evaluate VF to be in the same numerical space as the trip count.
+ unsigned EstimatedVF = VF.getKnownMinValue();
+ if (VF.isScalable() && BestKnownTC->isFixed())
+ EstimatedVF = getEstimatedRuntimeVF(VF, VScaleForTuning);
+
// At least one iteration must be scalar when this constraint holds. So the
// maximum available iterations for interleaving is one less.
unsigned AvailableTC = requiresScalarEpilogue(VF.isVector())
- ? BestKnownTC->getFixedValue() - 1
- : BestKnownTC->getFixedValue();
+ ? BestKnownTC->getKnownMinValue() - 1
+ : BestKnownTC->getKnownMinValue();
unsigned InterleaveCountLB = bit_floor(std::max(
1u, std::min(AvailableTC / (EstimatedVF * 2), MaxInterleaveCount)));
diff --git a/llvm/test/Transforms/LoopVectorize/AArch64/sve-vscale-based-trip-counts.ll b/llvm/test/Transforms/LoopVectorize/AArch64/sve-vscale-based-trip-counts.ll
index e2c7469a97819..dd1606c0f349a 100644
--- a/llvm/test/Transforms/LoopVectorize/AArch64/sve-vscale-based-trip-counts.ll
+++ b/llvm/test/Transforms/LoopVectorize/AArch64/sve-vscale-based-trip-counts.ll
@@ -10,62 +10,35 @@ define void @vscale_mul_4(ptr noalias noundef readonly captures(none) %a, ptr no
; CHECK-NEXT: [[TMP0:%.*]] = tail call i64 @llvm.vscale.i64()
; CHECK-NEXT: [[TMP1:%.*]] = shl nuw nsw i64 [[TMP0]], 2
; CHECK-NEXT: [[TMP2:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP3:%.*]] = mul nuw i64 [[TMP2]], 8
-; CHECK-NEXT: [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[TMP1]], [[TMP3]]
-; CHECK-NEXT: br i1 [[MIN_ITERS_CHECK]], label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
-; CHECK: [[VECTOR_PH]]:
+; CHECK-NEXT: [[TMP3:%.*]] = mul nuw i64 [[TMP2]], 4
; CHECK-NEXT: [[TMP4:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP5:%.*]] = mul nuw i64 [[TMP4]], 8
+; CHECK-NEXT: [[TMP5:%.*]] = mul nuw i64 [[TMP4]], 4
; CHECK-NEXT: [[N_MOD_VF:%.*]] = urem i64 [[TMP1]], [[TMP5]]
; CHECK-NEXT: [[N_VEC:%.*]] = sub i64 [[TMP1]], [[N_MOD_VF]]
-; CHECK-NEXT: [[TMP10:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP7:%.*]] = mul nuw i64 [[TMP10]], 8
-; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
-; CHECK: [[VECTOR_BODY]]:
-; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-NEXT: [[TMP13:%.*]] = getelementptr inbounds nuw float, ptr [[A]], i64 [[INDEX]]
-; CHECK-NEXT: [[TMP14:%.*]] = getelementptr inbounds nuw float, ptr [[TMP13]], i32 0
-; CHECK-NEXT: [[TMP18:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP11:%.*]] = mul nuw i64 [[TMP18]], 4
-; CHECK-NEXT: [[TMP26:%.*]] = getelementptr inbounds nuw float, ptr [[TMP13]], i64 [[TMP11]]
-; CHECK-NEXT: [[WIDE_LOAD2:%.*]] = load <vscale x 4 x float>, ptr [[TMP14]], align 4
-; CHECK-NEXT: [[WIDE_LOAD1:%.*]] = load <vscale x 4 x float>, ptr [[TMP26]], align 4
-; CHECK-NEXT: [[TMP12:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i64 [[INDEX]]
-; CHECK-NEXT: [[TMP17:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i32 0
-; CHECK-NEXT: [[TMP15:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP16:%.*]] = mul nuw i64 [[TMP15]], 4
-; CHECK-NEXT: [[TMP27:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i64 [[TMP16]]
-; CHECK-NEXT: [[WIDE_LOAD3:%.*]] = load <vscale x 4 x float>, ptr [[TMP17]], align 4
-; CHECK-NEXT: [[WIDE_LOAD4:%.*]] = load <vscale x 4 x float>, ptr [[TMP27]], align 4
-; CHECK-NEXT: [[TMP19:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD2]], [[WIDE_LOAD3]]
-; CHECK-NEXT: [[TMP28:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD1]], [[WIDE_LOAD4]]
-; CHECK-NEXT: [[TMP20:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP21:%.*]] = mul nuw i64 [[TMP20]], 4
-; CHECK-NEXT: [[TMP22:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i64 [[TMP21]]
-; CHECK-NEXT: store <vscale x 4 x float> [[TMP19]], ptr [[TMP17]], align 4
-; CHECK-NEXT: store <vscale x 4 x float> [[TMP28]], ptr [[TMP22]], align 4
-; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP7]]
-; CHECK-NEXT: [[TMP23:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT: br i1 [[TMP23]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
-; CHECK: [[MIDDLE_BLOCK]]:
+; CHECK-NEXT: [[TMP6:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT: [[TMP7:%.*]] = mul nuw i64 [[TMP6]], 4
+; CHECK-NEXT: [[TMP8:%.*]] = getelementptr inbounds nuw float, ptr [[A]], i32 0
+; CHECK-NEXT: [[WIDE_LOAD:%.*]] = load <vscale x 4 x float>, ptr [[TMP8]], align 4
+; CHECK-NEXT: [[TMP9:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i32 0
+; CHECK-NEXT: [[WIDE_LOAD1:%.*]] = load <vscale x 4 x float>, ptr [[TMP9]], align 4
+; CHECK-NEXT: [[TMP10:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD]], [[WIDE_LOAD1]]
+; CHECK-NEXT: [[TMP11:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i32 0
+; CHECK-NEXT: store <vscale x 4 x float> [[TMP10]], ptr [[TMP11]], align 4
; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[TMP1]], [[N_VEC]]
-; CHECK-NEXT: br i1 [[CMP_N]], label %[[FOR_COND_CLEANUP:.*]], label %[[SCALAR_PH]]
-; CHECK: [[SCALAR_PH]]:
-; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
-; CHECK-NEXT: br label %[[FOR_BODY:.*]]
+; CHECK-NEXT: br i1 [[CMP_N]], label %[[FOR_COND_CLEANUP:.*]], label %[[FOR_BODY:.*]]
; CHECK: [[FOR_COND_CLEANUP]]:
; CHECK-NEXT: ret void
; CHECK: [[FOR_BODY]]:
-; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[INDVARS_IV_NEXT:%.*]], %[[FOR_BODY]] ]
+; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], %[[FOR_BODY]] ], [ [[N_VEC]], %[[ENTRY]] ]
; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds nuw float, ptr [[A]], i64 [[INDVARS_IV]]
-; CHECK-NEXT: [[TMP24:%.*]] = load float, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT: [[TMP12:%.*]] = load float, ptr [[ARRAYIDX]], align 4
; CHECK-NEXT: [[ARRAYIDX3:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i64 [[INDVARS_IV]]
-; CHECK-NEXT: [[TMP25:%.*]] = load float, ptr [[ARRAYIDX3]], align 4
-; CHECK-NEXT: [[MUL4:%.*]] = fmul float [[TMP24]], [[TMP25]]
+; CHECK-NEXT: [[TMP13:%.*]] = load float, ptr [[ARRAYIDX3]], align 4
+; CHECK-NEXT: [[MUL4:%.*]] = fmul float [[TMP12]], [[TMP13]]
; CHECK-NEXT: store float [[MUL4]], ptr [[ARRAYIDX3]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[TMP1]]
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
;
entry:
%0 = tail call i64 @llvm.vscale.i64()
@@ -136,7 +109,7 @@ define void @vscale_mul_8(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: store float [[MUL5]], ptr [[ARRAYIDX4]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[MUL1]]
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
+; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP3:![0-9]+]]
;
entry:
%0 = tail call i64 @llvm.vscale.i64()
@@ -166,43 +139,30 @@ define void @vscale_mul_12(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: [[TMP0:%.*]] = tail call i64 @llvm.vscale.i64()
; CHECK-NEXT: [[MUL1:%.*]] = mul nuw nsw i64 [[TMP0]], 12
; CHECK-NEXT: [[TMP1:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP2:%.*]] = mul nuw i64 [[TMP1]], 8
+; CHECK-NEXT: [[TMP2:%.*]] = mul nuw i64 [[TMP1]], 4
; CHECK-NEXT: [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[MUL1]], [[TMP2]]
; CHECK-NEXT: br i1 [[MIN_ITERS_CHECK]], label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: [[TMP3:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP4:%.*]] = mul nuw i64 [[TMP3]], 8
+; CHECK-NEXT: [[TMP4:%.*]] = mul nuw i64 [[TMP3]], 4
; CHECK-NEXT: [[N_MOD_VF:%.*]] = urem i64 [[MUL1]], [[TMP4]]
; CHECK-NEXT: [[N_VEC:%.*]] = sub i64 [[MUL1]], [[N_MOD_VF]]
; CHECK-NEXT: [[TMP5:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP6:%.*]] = mul nuw i64 [[TMP5]], 8
+; CHECK-NEXT: [[TMP6:%.*]] = mul nuw i64 [[TMP5]], 4
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[TMP7:%.*]] = getelementptr inbounds nuw float, ptr [[A]], i64 [[INDEX]]
; CHECK-NEXT: [[TMP8:%.*]] = getelementptr inbounds nuw float, ptr [[TMP7]], i32 0
-; CHECK-NEXT: [[TMP9:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP10:%.*]] = mul nuw i64 [[TMP9]], 4
-; CHECK-NEXT: [[TMP11:%.*]] = getelementptr inbounds nuw float, ptr [[TMP7]], i64 [[TMP10]]
-; CHECK-NEXT: [[WIDE_LOAD1:%.*]] = load <vscale x 4 x float>, ptr [[TMP8]], align 4
-; CHECK-NEXT: [[WIDE_LOAD2:%.*]] = load <vscale x 4 x float>, ptr [[TMP11]], align 4
-; CHECK-NEXT: [[TMP12:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i64 [[INDEX]]
-; CHECK-NEXT: [[TMP13:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i32 0
-; CHECK-NEXT: [[TMP14:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP15:%.*]] = mul nuw i64 [[TMP14]], 4
-; CHECK-NEXT: [[TMP16:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i64 [[TMP15]]
-; CHECK-NEXT: [[WIDE_LOAD3:%.*]] = load <vscale x 4 x float>, ptr [[TMP13]], align 4
-; CHECK-NEXT: [[WIDE_LOAD4:%.*]] = load <vscale x 4 x float>, ptr [[TMP16]], align 4
-; CHECK-NEXT: [[TMP18:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD1]], [[WIDE_LOAD3]]
-; CHECK-NEXT: [[TMP25:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD2]], [[WIDE_LOAD4]]
-; CHECK-NEXT: [[TMP19:%.*]] = call i64 @llvm.vscale.i64()
-; CHECK-NEXT: [[TMP20:%.*]] = mul nuw i64 [[TMP19]], 4
-; CHECK-NEXT: [[TMP21:%.*]] = getelementptr inbounds nuw float, ptr [[TMP12]], i64 [[TMP20]]
-; CHECK-NEXT: store <vscale x 4 x float> [[TMP18]], ptr [[TMP13]], align 4
-; CHECK-NEXT: store <vscale x 4 x float> [[TMP25]], ptr [[TMP21]], align 4
+; CHECK-NEXT: [[WIDE_LOAD:%.*]] = load <vscale x 4 x float>, ptr [[TMP8]], align 4
+; CHECK-NEXT: [[TMP9:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i64 [[INDEX]]
+; CHECK-NEXT: [[TMP10:%.*]] = getelementptr inbounds nuw float, ptr [[TMP9]], i32 0
+; CHECK-NEXT: [[WIDE_LOAD1:%.*]] = load <vscale x 4 x float>, ptr [[TMP10]], align 4
+; CHECK-NEXT: [[TMP11:%.*]] = fmul <vscale x 4 x float> [[WIDE_LOAD]], [[WIDE_LOAD1]]
+; CHECK-NEXT: store <vscale x 4 x float> [[TMP11]], ptr [[TMP10]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP6]]
-; CHECK-NEXT: [[TMP22:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT: br i1 [[TMP22]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP5:![0-9]+]]
+; CHECK-NEXT: [[TMP12:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT: br i1 [[TMP12]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[MUL1]], [[N_VEC]]
; CHECK-NEXT: br i1 [[CMP_N]], label %[[FOR_COND_CLEANUP:.*]], label %[[SCALAR_PH]]
@@ -214,14 +174,14 @@ define void @vscale_mul_12(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK: [[FOR_BODY]]:
; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[INDVARS_IV_NEXT:%.*]], %[[FOR_BODY]] ]
; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds nuw float, ptr [[A]], i64 [[INDVARS_IV]]
-; CHECK-NEXT: [[TMP23:%.*]] = load float, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT: [[TMP13:%.*]] = load float, ptr [[ARRAYIDX]], align 4
; CHECK-NEXT: [[ARRAYIDX4:%.*]] = getelementptr inbounds nuw float, ptr [[B]], i64 [[INDVARS_IV]]
-; CHECK-NEXT: [[TMP24:%.*]] = load float, ptr [[ARRAYIDX4]], align 4
-; CHECK-NEXT: [[MUL5:%.*]] = fmul float [[TMP23]], [[TMP24]]
+; CHECK-NEXT: [[TMP14:%.*]] = load float, ptr [[ARRAYIDX4]], align 4
+; CHECK-NEXT: [[MUL5:%.*]] = fmul float [[TMP13]], [[TMP14]]
; CHECK-NEXT: store float [[MUL5]], ptr [[ARRAYIDX4]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[MUL1]]
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
+; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP5:![0-9]+]]
;
entry:
%0 = tail call i64 @llvm.vscale.i64()
@@ -287,7 +247,7 @@ define void @vscale_mul_31(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: store <vscale x 4 x float> [[TMP18]], ptr [[TMP21]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP6]]
; CHECK-NEXT: [[TMP22:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT: br i1 [[TMP22]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP7:![0-9]+]]
+; CHECK-NEXT: br i1 [[TMP22]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[MUL1]], [[N_VEC]]
; CHECK-NEXT: br i1 [[CMP_N]], label %[[FOR_COND_CLEANUP:.*]], label %[[SCALAR_PH]]
@@ -306,7 +266,7 @@ define void @vscale_mul_31(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: store float [[MUL5]], ptr [[ARRAYIDX4]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[MUL1]]
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
+; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP7:![0-9]+]]
;
entry:
%0 = tail call i64 @llvm.vscale.i64()
@@ -372,7 +332,7 @@ define void @vscale_mul_64(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: store <vscale x 4 x float> [[TMP18]], ptr [[TMP21]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP6]]
; CHECK-NEXT: [[TMP22:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT: br i1 [[TMP22]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP9:![0-9]+]]
+; CHECK-NEXT: br i1 [[TMP22]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[MUL1]], [[N_VEC]]
; CHECK-NEXT: br i1 [[CMP_N]], label %[[FOR_COND_CLEANUP:.*]], label %[[SCALAR_PH]]
@@ -391,7 +351,7 @@ define void @vscale_mul_64(ptr noalias noundef readonly captures(none) %a, ptr n
; CHECK-NEXT: store float [[MUL5]], ptr [[ARRAYIDX4]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[MUL1]]
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP10:![0-9]+]]
+; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label %[[FOR_COND_CLEANUP]], label %[[FOR_BODY]], !llvm.loop [[LOOP9:![0-9]+]]
;
entry:
%0 = tail call i64 @llvm.vscale.i64()
@@ -419,14 +379,13 @@ declare i64 @llvm.vscale.i64()
attributes #0 = { vscale_range(1,16) "target-features"="+sve" }
;.
; CHECK: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]], [[META2:![0-9]+]]}
-; CHECK: [[META1]] = !{!"llvm.loop.isvectorized", i32 1}
-; CHECK: [[META2]] = !{!"llvm.loop.unroll.runtime.disable"}
-; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META2]], [[META1]]}
+; CHECK: [[META1]] = !{!"llvm.loop.unroll.runtime.disable"}
+; CHECK: [[META2]] = !{!"llvm.loop.isvectorized", i32 1}
+; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META1]], [[META2]]}
; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META2]], [[META1]]}
; CHECK: [[LOOP5]] = distinct !{[[LOOP5]], [[META1]], [[META2]]}
; CHECK: [[LOOP6]] = distinct !{[[LOOP6]], [[META2]], [[META1]]}
; CHECK: [[LOOP7]] = distinct !{[[LOOP7]], [[META1]], [[META2]]}
; CHECK: [[LOOP8]] = distinct !{[[LOOP8]], [[META2]], [[META1]]}
; CHECK: [[LOOP9]] = distinct !{[[LOOP9]], [[META1]], [[META2]]}
-; CHECK: [[LOOP10]] = distinct !{[[LOOP10]], [[META2]], [[META1]]}
;.
|
preames
reviewed
Jul 9, 2025
| return ElementCount::getScalable(1); | ||
|
|
||
| if (auto *Mul = dyn_cast<SCEVMulExpr>(ExitCount)) | ||
| if (Mul->getNumOperands() == 2 && isa<SCEVConstant>(Mul->getOperand(0)) && |
There was a problem hiding this comment.
Do we need to check overflow here?
There was a problem hiding this comment.
Fixed both in terms of requiring NUW flags and ensuring the constant fits within the range of ElementCount.
| @@ -423,7 +423,26 @@ static bool hasIrregularType(Type *Ty, const DataLayout &DL) { | |||
| /// ElementCount to include loops whose trip count is a function of vscale. | |||
| static ElementCount getSmallConstantTripCount(ScalarEvolution *SE, | |||
| const Loop *L) { | |||
| return ElementCount::getFixed(SE->getSmallConstantTripCount(L)); | |||
| if (unsigned ExpectedTC = SE->getSmallConstantTripCount(L)) | |||
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This routine seems like it should live on SCEV itself. I was originally going to propose we change getSmallConstantTripCount to return ElementCount, but that looks mildly invasive. Maybe for the moment have a "getSmallConstantTripElementCount"? Not a huge fan of that name, but it's at least close...
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That's the route I started with but was advised to make the function specific to LoopVectorize, presumably until such a time that its applicability extends beyond vectorisation.
| auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop); | ||
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| // For fixed length VFs treat a scalable trip count as unknown. | ||
| if (BestKnownTC && (BestKnownTC->isFixed() || VF.isScalable())) { |
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Style wise:
if (auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop);
BestKnownTC && (BestKnownTC->isFixed() || VF.isScalable())) {
| // At least one iteration must be scalar when this constraint holds. So the | ||
| // maximum available iterations for interleaving is one less. | ||
| unsigned AvailableTC = requiresScalarEpilogue(VF.isVector()) | ||
| ? BestKnownTC->getFixedValue() - 1 | ||
| : BestKnownTC->getFixedValue(); | ||
| ? BestKnownTC->getKnownMinValue() - 1 |
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For a scalable trip count, using the min value here seems off. Shouldn't we be using vscalefortuning here?
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I don't think it matters because when BestKnownTC is scalable EstimatedVF must also be scalable with all uses being to create ratios between the two. By using getKnownMinValue() we're just removing the common vscale factor.
That said, I don't much like getKnownMinValue() so have changed the implementation to force everything to unsigned, be they know values or estimates, which as expected does not seem to affect the result but I feel looks more readable?
Please let me know if you'd rather I stick with the original approach.
david-arm
reviewed
Jul 14, 2025
| if (auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop)) { | ||
| // ConstantMax from PSE, failing that. For fixed length VFs treat a scalable | ||
| // trip count as if unknown. | ||
| if (auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop); |
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I know this works, but I personally find it more readable to avoid multiple statements separated by ; within an if(...) block, i.e. something like
auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop);
if (BestKnownTC && (BestKnownTC->isFixed() || VF.isScalable())
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That is the style I originally used and @preames requested it be changed to this.
| br i1 %exitcond.not, label %for.cond.cleanup, label %for.body | ||
| } | ||
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| ; The known component of ElementCount is a 32-bit value. |
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Shouldn't that be The known component of ElementCount does not fit into 32 bits?
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No. This is stating a fact, namely "ElementCount stores its known component as a 32-bit value", so as to explain why the test's trip count is too big for ElementCount.
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Update getSmallConstantTripCount() to return scalable ElementCount values that is used to acurrately determine the maximum value for UF, namely:
TripCount / VF ==> X * VScale / Y * VScale ==> X / Y
This improves the chances of being able to remove the scalar loop and also fixes an issue where a UF=2 is choosen for a scalar loop with exactly VF(= X * VScale) iterations.