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[LoopVectorize] Add cost of generating tail-folding mask to the loop #130565

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Mar 21, 2025
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[LoopVectorize] Add cost of generating tail-folding mask to the loop #130565

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[LoopVectorize] Add cost of generating tail-folding mask to the loop
david-arm Mar 18, 2025
114a4c0
Address review comments
david-arm Mar 19, 2025
7e6d781
Address review comments
david-arm Mar 20, 2025
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25 changes: 25 additions & 0 deletions llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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Expand Up @@ -5610,6 +5610,31 @@ InstructionCost LoopVectorizationCostModel::expectedCost(ElementCount VF) {
Cost += BlockCost;
}

#ifndef NDEBUG
// TODO: We're effectively having to duplicate the code from
// VPInstruction::computeCost, which is ugly. This isn't meant to be a fully
// accurate representation of the cost of tail-folding - it exists purely to
// stop asserts firing when the legacy cost doesn't match the VPlan cost.
if (!VF.isScalar() && foldTailByMasking()) {
TailFoldingStyle Style = getTailFoldingStyle();
LLVMContext &Context = TheLoop->getHeader()->getContext();
Type *I1Ty = IntegerType::getInt1Ty(Context);
Type *IndTy = Legal->getWidestInductionType();
TTI::TargetCostKind CostKind = TTI::TCK_RecipThroughput;
if (Style == TailFoldingStyle::DataWithEVL) {
Type *I32Ty = IntegerType::getInt32Ty(Context);
IntrinsicCostAttributes Attrs(Intrinsic::experimental_get_vector_length,
I32Ty, {IndTy, I32Ty, I1Ty});
Cost += TTI.getIntrinsicInstrCost(Attrs, CostKind);
} else if (useActiveLaneMask(Style)) {
VectorType *RetTy = VectorType::get(I1Ty, VF);
IntrinsicCostAttributes Attrs(Intrinsic::get_active_lane_mask, RetTy,
{IndTy, IndTy});
Cost += TTI.getIntrinsicInstrCost(Attrs, CostKind);
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I am wondering if it would be cleaner to handle this in the caller of expectedCost, where we have the VPlans available. With that, we could just iterate over all recipes in the loop region and compute the costs for ActiveLaneMask/EVL using the VPlan-based cost model and add them to the cost returned by expectedCost?

This might be more scalable for future use-cases.

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Fair enough!

}
}
#endif

return Cost;
}

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16 changes: 16 additions & 0 deletions llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
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Expand Up @@ -801,6 +801,22 @@ InstructionCost VPInstruction::computeCost(ElementCount VF,
cast<VectorType>(VectorTy), Mask,
Ctx.CostKind, VF.getKnownMinValue() - 1);
}
case VPInstruction::ActiveLaneMask: {
Type *Arg0Ty = Ctx.Types.inferScalarType(getOperand(0));
Type *Arg1Ty = Ctx.Types.inferScalarType(getOperand(1));
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Given get.active.lane.mask requires both parameters to be the same type, do we need to calculate Arg1Ty?

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VPTypeAnalysis should already assert that both types are the same, so would probably be good to remove here.

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Done

Type *RetTy = toVectorTy(Type::getInt1Ty(Ctx.LLVMCtx), VF);
IntrinsicCostAttributes Attrs(Intrinsic::get_active_lane_mask, RetTy,
{Arg0Ty, Arg1Ty});
return Ctx.TTI.getIntrinsicInstrCost(Attrs, Ctx.CostKind);
}
case VPInstruction::ExplicitVectorLength: {
Type *Arg0Ty = Ctx.Types.inferScalarType(getOperand(0));
Type *I32Ty = Type::getInt32Ty(Ctx.LLVMCtx);
Type *I1Ty = Type::getInt1Ty(Ctx.LLVMCtx);
IntrinsicCostAttributes Attrs(Intrinsic::experimental_get_vector_length,
I32Ty, {Arg0Ty, I32Ty, I1Ty});
return Ctx.TTI.getIntrinsicInstrCost(Attrs, Ctx.CostKind);
}
default:
// TODO: Compute cost other VPInstructions once the legacy cost model has
// been retired.
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169 changes: 35 additions & 134 deletions llvm/test/Transforms/LoopVectorize/AArch64/conditional-branches-cost.ll
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40 changes: 20 additions & 20 deletions llvm/test/Transforms/LoopVectorize/AArch64/induction-costs-sve.ll
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Expand Up @@ -99,49 +99,49 @@ define void @iv_casts(ptr %dst, ptr %src, i32 %x, i64 %N) #0 {
; PRED-NEXT: br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_MEMCHECK:.*]]
; PRED: [[VECTOR_MEMCHECK]]:
; PRED-NEXT: [[TMP1:%.*]] = call i64 @llvm.vscale.i64()
; PRED-NEXT: [[TMP2:%.*]] = mul i64 [[TMP1]], 8
; PRED-NEXT: [[TMP2:%.*]] = mul i64 [[TMP1]], 16
; PRED-NEXT: [[TMP3:%.*]] = sub i64 [[DST1]], [[SRC2]]
; PRED-NEXT: [[DIFF_CHECK:%.*]] = icmp ult i64 [[TMP3]], [[TMP2]]
; PRED-NEXT: br i1 [[DIFF_CHECK]], label %[[SCALAR_PH]], label %[[VECTOR_PH:.*]]
; PRED: [[VECTOR_PH]]:
; PRED-NEXT: [[TMP4:%.*]] = call i64 @llvm.vscale.i64()
; PRED-NEXT: [[TMP5:%.*]] = mul i64 [[TMP4]], 8
; PRED-NEXT: [[TMP5:%.*]] = mul i64 [[TMP4]], 16
; PRED-NEXT: [[TMP8:%.*]] = sub i64 [[TMP5]], 1
; PRED-NEXT: [[N_RND_UP:%.*]] = add i64 [[TMP0]], [[TMP8]]
; PRED-NEXT: [[N_MOD_VF:%.*]] = urem i64 [[N_RND_UP]], [[TMP5]]
; PRED-NEXT: [[N_VEC:%.*]] = sub i64 [[N_RND_UP]], [[N_MOD_VF]]
; PRED-NEXT: [[TMP9:%.*]] = call i64 @llvm.vscale.i64()
; PRED-NEXT: [[TMP10:%.*]] = mul i64 [[TMP9]], 8
; PRED-NEXT: [[BROADCAST_SPLATINSERT:%.*]] = insertelement <vscale x 8 x i32> poison, i32 [[X]], i64 0
; PRED-NEXT: [[BROADCAST_SPLAT:%.*]] = shufflevector <vscale x 8 x i32> [[BROADCAST_SPLATINSERT]], <vscale x 8 x i32> poison, <vscale x 8 x i32> zeroinitializer
; PRED-NEXT: [[TMP10:%.*]] = mul i64 [[TMP9]], 16
; PRED-NEXT: [[BROADCAST_SPLATINSERT:%.*]] = insertelement <vscale x 16 x i32> poison, i32 [[X]], i64 0
; PRED-NEXT: [[BROADCAST_SPLAT:%.*]] = shufflevector <vscale x 16 x i32> [[BROADCAST_SPLATINSERT]], <vscale x 16 x i32> poison, <vscale x 16 x i32> zeroinitializer
; PRED-NEXT: [[TMP11:%.*]] = call i64 @llvm.vscale.i64()
; PRED-NEXT: [[TMP12:%.*]] = mul i64 [[TMP11]], 8
; PRED-NEXT: [[TMP12:%.*]] = mul i64 [[TMP11]], 16
; PRED-NEXT: [[TMP13:%.*]] = sub i64 [[TMP0]], [[TMP12]]
; PRED-NEXT: [[TMP14:%.*]] = icmp ugt i64 [[TMP0]], [[TMP12]]
; PRED-NEXT: [[TMP15:%.*]] = select i1 [[TMP14]], i64 [[TMP13]], i64 0
; PRED-NEXT: [[ACTIVE_LANE_MASK_ENTRY:%.*]] = call <vscale x 8 x i1> @llvm.get.active.lane.mask.nxv8i1.i64(i64 0, i64 [[TMP0]])
; PRED-NEXT: [[TMP16:%.*]] = trunc <vscale x 8 x i32> [[BROADCAST_SPLAT]] to <vscale x 8 x i16>
; PRED-NEXT: [[ACTIVE_LANE_MASK_ENTRY:%.*]] = call <vscale x 16 x i1> @llvm.get.active.lane.mask.nxv16i1.i64(i64 0, i64 [[TMP0]])
; PRED-NEXT: [[TMP16:%.*]] = trunc <vscale x 16 x i32> [[BROADCAST_SPLAT]] to <vscale x 16 x i16>
; PRED-NEXT: br label %[[VECTOR_BODY:.*]]
; PRED: [[VECTOR_BODY]]:
; PRED-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; PRED-NEXT: [[ACTIVE_LANE_MASK:%.*]] = phi <vscale x 8 x i1> [ [[ACTIVE_LANE_MASK_ENTRY]], %[[VECTOR_PH]] ], [ [[ACTIVE_LANE_MASK_NEXT:%.*]], %[[VECTOR_BODY]] ]
; PRED-NEXT: [[ACTIVE_LANE_MASK:%.*]] = phi <vscale x 16 x i1> [ [[ACTIVE_LANE_MASK_ENTRY]], %[[VECTOR_PH]] ], [ [[ACTIVE_LANE_MASK_NEXT:%.*]], %[[VECTOR_BODY]] ]
; PRED-NEXT: [[TMP17:%.*]] = add i64 [[INDEX]], 0
; PRED-NEXT: [[TMP18:%.*]] = getelementptr i8, ptr [[SRC]], i64 [[TMP17]]
; PRED-NEXT: [[TMP19:%.*]] = getelementptr i8, ptr [[TMP18]], i32 0
; PRED-NEXT: [[WIDE_MASKED_LOAD:%.*]] = call <vscale x 8 x i8> @llvm.masked.load.nxv8i8.p0(ptr [[TMP19]], i32 1, <vscale x 8 x i1> [[ACTIVE_LANE_MASK]], <vscale x 8 x i8> poison)
; PRED-NEXT: [[TMP20:%.*]] = zext <vscale x 8 x i8> [[WIDE_MASKED_LOAD]] to <vscale x 8 x i16>
; PRED-NEXT: [[TMP21:%.*]] = mul <vscale x 8 x i16> [[TMP20]], [[TMP16]]
; PRED-NEXT: [[TMP22:%.*]] = zext <vscale x 8 x i8> [[WIDE_MASKED_LOAD]] to <vscale x 8 x i16>
; PRED-NEXT: [[TMP23:%.*]] = or <vscale x 8 x i16> [[TMP21]], [[TMP22]]
; PRED-NEXT: [[TMP24:%.*]] = lshr <vscale x 8 x i16> [[TMP23]], trunc (<vscale x 8 x i32> splat (i32 1) to <vscale x 8 x i16>)
; PRED-NEXT: [[TMP25:%.*]] = trunc <vscale x 8 x i16> [[TMP24]] to <vscale x 8 x i8>
; PRED-NEXT: [[WIDE_MASKED_LOAD:%.*]] = call <vscale x 16 x i8> @llvm.masked.load.nxv16i8.p0(ptr [[TMP19]], i32 1, <vscale x 16 x i1> [[ACTIVE_LANE_MASK]], <vscale x 16 x i8> poison)
; PRED-NEXT: [[TMP24:%.*]] = zext <vscale x 16 x i8> [[WIDE_MASKED_LOAD]] to <vscale x 16 x i16>
; PRED-NEXT: [[TMP25:%.*]] = mul <vscale x 16 x i16> [[TMP24]], [[TMP16]]
; PRED-NEXT: [[TMP20:%.*]] = zext <vscale x 16 x i8> [[WIDE_MASKED_LOAD]] to <vscale x 16 x i16>
; PRED-NEXT: [[TMP21:%.*]] = or <vscale x 16 x i16> [[TMP25]], [[TMP20]]
; PRED-NEXT: [[TMP22:%.*]] = lshr <vscale x 16 x i16> [[TMP21]], trunc (<vscale x 16 x i32> splat (i32 1) to <vscale x 16 x i16>)
; PRED-NEXT: [[TMP23:%.*]] = trunc <vscale x 16 x i16> [[TMP22]] to <vscale x 16 x i8>
; PRED-NEXT: [[TMP26:%.*]] = getelementptr i8, ptr [[DST]], i64 [[TMP17]]
; PRED-NEXT: [[TMP27:%.*]] = getelementptr i8, ptr [[TMP26]], i32 0
; PRED-NEXT: call void @llvm.masked.store.nxv8i8.p0(<vscale x 8 x i8> [[TMP25]], ptr [[TMP27]], i32 1, <vscale x 8 x i1> [[ACTIVE_LANE_MASK]])
; PRED-NEXT: call void @llvm.masked.store.nxv16i8.p0(<vscale x 16 x i8> [[TMP23]], ptr [[TMP27]], i32 1, <vscale x 16 x i1> [[ACTIVE_LANE_MASK]])
; PRED-NEXT: [[INDEX_NEXT]] = add i64 [[INDEX]], [[TMP10]]
; PRED-NEXT: [[ACTIVE_LANE_MASK_NEXT]] = call <vscale x 8 x i1> @llvm.get.active.lane.mask.nxv8i1.i64(i64 [[INDEX]], i64 [[TMP15]])
; PRED-NEXT: [[TMP28:%.*]] = xor <vscale x 8 x i1> [[ACTIVE_LANE_MASK_NEXT]], splat (i1 true)
; PRED-NEXT: [[TMP29:%.*]] = extractelement <vscale x 8 x i1> [[TMP28]], i32 0
; PRED-NEXT: [[ACTIVE_LANE_MASK_NEXT]] = call <vscale x 16 x i1> @llvm.get.active.lane.mask.nxv16i1.i64(i64 [[INDEX]], i64 [[TMP15]])
; PRED-NEXT: [[TMP28:%.*]] = xor <vscale x 16 x i1> [[ACTIVE_LANE_MASK_NEXT]], splat (i1 true)
; PRED-NEXT: [[TMP29:%.*]] = extractelement <vscale x 16 x i1> [[TMP28]], i32 0
; PRED-NEXT: br i1 [[TMP29]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
; PRED: [[MIDDLE_BLOCK]]:
; PRED-NEXT: br i1 true, label %[[EXIT:.*]], label %[[SCALAR_PH]]
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