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[VPlan] Disable partial reductions again with EVL tail folding #167863

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Nov 14, 2025
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[VPlan] Disable partial reductions again with EVL tail folding #167863

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7869fe8
[VPlan] Disable partial reductions again with EVL tail folding
lukel97 Nov 13, 2025
3978a51
Merge branch 'main' into loop-vectorize/disable-partial-reductions-wi…
lukel97 Nov 14, 2025
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4 changes: 3 additions & 1 deletion llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8395,7 +8395,9 @@ VPlanPtr LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(
// ---------------------------------------------------------------------------
VPRecipeBuilder RecipeBuilder(*Plan, OrigLoop, TLI, &TTI, Legal, CM, PSE,
Builder, BlockMaskCache, LVer);
RecipeBuilder.collectScaledReductions(Range);
// TODO: Handle partial reductions with EVL tail folding.
if (!CM.foldTailWithEVL())
RecipeBuilder.collectScaledReductions(Range);

// Scan the body of the loop in a topological order to visit each basic block
// after having visited its predecessor basic blocks.
Expand Down
125 changes: 125 additions & 0 deletions llvm/test/Transforms/LoopVectorize/RISCV/partial-reduce-dot-product.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
; RUN: opt -passes=loop-vectorize -mattr=+v,+experimental-zvqdotq -prefer-predicate-over-epilogue=scalar-epilogue -S < %s | FileCheck %s --check-prefixes=CHECK,ZVQDOTQ
; RUN: opt -passes=loop-vectorize -mattr=+v -scalable-vectorization=off -prefer-predicate-over-epilogue=scalar-epilogue -S < %s | FileCheck %s --check-prefixes=FIXED,FIXED-V
; RUN: opt -passes=loop-vectorize -mattr=+v,+experimental-zvqdotq -scalable-vectorization=off -prefer-predicate-over-epilogue=scalar-epilogue -S < %s | FileCheck %s --check-prefixes=FIXED,FIXED-ZVQDOTQ
; RUN: opt -passes=loop-vectorize -mattr=+v,+experimental-zvqdotq -S < %s | FileCheck %s --check-prefixes=CHECK,TAILFOLD

; TODO: Remove -prefer-predicate-over-epilogue=scalar-epilogue when partial reductions with EVL tail folding is supported.

Expand Down Expand Up @@ -147,6 +148,37 @@ define i32 @vqdot(ptr %a, ptr %b) #0 {
; FIXED-ZVQDOTQ: for.exit:
; FIXED-ZVQDOTQ-NEXT: ret i32 [[TMP13]]
;
; TAILFOLD-LABEL: define i32 @vqdot(
; TAILFOLD-SAME: ptr [[A:%.*]], ptr [[B:%.*]]) #[[ATTR0:[0-9]+]] {
; TAILFOLD-NEXT: entry:
; TAILFOLD-NEXT: br label [[VECTOR_PH:%.*]]
; TAILFOLD: vector.ph:
; TAILFOLD-NEXT: br label [[VECTOR_BODY:%.*]]
; TAILFOLD: vector.body:
; TAILFOLD-NEXT: [[EVL_BASED_IV:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_EVL_NEXT:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[VEC_PHI:%.*]] = phi <vscale x 4 x i32> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP7:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[AVL:%.*]] = phi i64 [ 1024, [[VECTOR_PH]] ], [ [[AVL_NEXT:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[TMP0:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 [[AVL]], i32 4, i1 true)
; TAILFOLD-NEXT: [[TMP1:%.*]] = getelementptr i8, ptr [[A]], i64 [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[VP_OP_LOAD:%.*]] = call <vscale x 4 x i8> @llvm.vp.load.nxv4i8.p0(ptr align 1 [[TMP1]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP2:%.*]] = sext <vscale x 4 x i8> [[VP_OP_LOAD]] to <vscale x 4 x i32>
; TAILFOLD-NEXT: [[TMP3:%.*]] = getelementptr i8, ptr [[B]], i64 [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[VP_OP_LOAD1:%.*]] = call <vscale x 4 x i8> @llvm.vp.load.nxv4i8.p0(ptr align 1 [[TMP3]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP4:%.*]] = sext <vscale x 4 x i8> [[VP_OP_LOAD1]] to <vscale x 4 x i32>
; TAILFOLD-NEXT: [[TMP5:%.*]] = mul <vscale x 4 x i32> [[TMP4]], [[TMP2]]
; TAILFOLD-NEXT: [[TMP6:%.*]] = add <vscale x 4 x i32> [[TMP5]], [[VEC_PHI]]
; TAILFOLD-NEXT: [[TMP7]] = call <vscale x 4 x i32> @llvm.vp.merge.nxv4i32(<vscale x 4 x i1> splat (i1 true), <vscale x 4 x i32> [[TMP6]], <vscale x 4 x i32> [[VEC_PHI]], i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP8:%.*]] = zext i32 [[TMP0]] to i64
; TAILFOLD-NEXT: [[INDEX_EVL_NEXT]] = add nuw i64 [[TMP8]], [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[AVL_NEXT]] = sub nuw i64 [[AVL]], [[TMP8]]
; TAILFOLD-NEXT: [[TMP9:%.*]] = icmp eq i64 [[AVL_NEXT]], 0
; TAILFOLD-NEXT: br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
; TAILFOLD: middle.block:
; TAILFOLD-NEXT: [[TMP10:%.*]] = call i32 @llvm.vector.reduce.add.nxv4i32(<vscale x 4 x i32> [[TMP7]])
; TAILFOLD-NEXT: br label [[FOR_EXIT:%.*]]
; TAILFOLD: for.exit:
; TAILFOLD-NEXT: ret i32 [[TMP10]]
;
entry:
br label %for.body

Expand Down Expand Up @@ -309,6 +341,37 @@ define i32 @vqdotu(ptr %a, ptr %b) #0 {
; FIXED-ZVQDOTQ: for.exit:
; FIXED-ZVQDOTQ-NEXT: ret i32 [[TMP13]]
;
; TAILFOLD-LABEL: define i32 @vqdotu(
; TAILFOLD-SAME: ptr [[A:%.*]], ptr [[B:%.*]]) #[[ATTR0]] {
; TAILFOLD-NEXT: entry:
; TAILFOLD-NEXT: br label [[VECTOR_PH:%.*]]
; TAILFOLD: vector.ph:
; TAILFOLD-NEXT: br label [[VECTOR_BODY:%.*]]
; TAILFOLD: vector.body:
; TAILFOLD-NEXT: [[EVL_BASED_IV:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_EVL_NEXT:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[VEC_PHI:%.*]] = phi <vscale x 4 x i32> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP7:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[AVL:%.*]] = phi i64 [ 1024, [[VECTOR_PH]] ], [ [[AVL_NEXT:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[TMP0:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 [[AVL]], i32 4, i1 true)
; TAILFOLD-NEXT: [[TMP1:%.*]] = getelementptr i8, ptr [[A]], i64 [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[VP_OP_LOAD:%.*]] = call <vscale x 4 x i8> @llvm.vp.load.nxv4i8.p0(ptr align 1 [[TMP1]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP2:%.*]] = zext <vscale x 4 x i8> [[VP_OP_LOAD]] to <vscale x 4 x i32>
; TAILFOLD-NEXT: [[TMP3:%.*]] = getelementptr i8, ptr [[B]], i64 [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[VP_OP_LOAD1:%.*]] = call <vscale x 4 x i8> @llvm.vp.load.nxv4i8.p0(ptr align 1 [[TMP3]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP4:%.*]] = zext <vscale x 4 x i8> [[VP_OP_LOAD1]] to <vscale x 4 x i32>
; TAILFOLD-NEXT: [[TMP5:%.*]] = mul <vscale x 4 x i32> [[TMP4]], [[TMP2]]
; TAILFOLD-NEXT: [[TMP6:%.*]] = add <vscale x 4 x i32> [[TMP5]], [[VEC_PHI]]
; TAILFOLD-NEXT: [[TMP7]] = call <vscale x 4 x i32> @llvm.vp.merge.nxv4i32(<vscale x 4 x i1> splat (i1 true), <vscale x 4 x i32> [[TMP6]], <vscale x 4 x i32> [[VEC_PHI]], i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP8:%.*]] = zext i32 [[TMP0]] to i64
; TAILFOLD-NEXT: [[INDEX_EVL_NEXT]] = add nuw i64 [[TMP8]], [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[AVL_NEXT]] = sub nuw i64 [[AVL]], [[TMP8]]
; TAILFOLD-NEXT: [[TMP9:%.*]] = icmp eq i64 [[AVL_NEXT]], 0
; TAILFOLD-NEXT: br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP3:![0-9]+]]
; TAILFOLD: middle.block:
; TAILFOLD-NEXT: [[TMP10:%.*]] = call i32 @llvm.vector.reduce.add.nxv4i32(<vscale x 4 x i32> [[TMP7]])
; TAILFOLD-NEXT: br label [[FOR_EXIT:%.*]]
; TAILFOLD: for.exit:
; TAILFOLD-NEXT: ret i32 [[TMP10]]
;
entry:
br label %for.body

Expand Down Expand Up @@ -471,6 +534,37 @@ define i32 @vqdotsu(ptr %a, ptr %b) #0 {
; FIXED-ZVQDOTQ: for.exit:
; FIXED-ZVQDOTQ-NEXT: ret i32 [[TMP13]]
;
; TAILFOLD-LABEL: define i32 @vqdotsu(
; TAILFOLD-SAME: ptr [[A:%.*]], ptr [[B:%.*]]) #[[ATTR0]] {
; TAILFOLD-NEXT: entry:
; TAILFOLD-NEXT: br label [[VECTOR_PH:%.*]]
; TAILFOLD: vector.ph:
; TAILFOLD-NEXT: br label [[VECTOR_BODY:%.*]]
; TAILFOLD: vector.body:
; TAILFOLD-NEXT: [[EVL_BASED_IV:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_EVL_NEXT:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[VEC_PHI:%.*]] = phi <vscale x 4 x i32> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP7:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[AVL:%.*]] = phi i64 [ 1024, [[VECTOR_PH]] ], [ [[AVL_NEXT:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[TMP0:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 [[AVL]], i32 4, i1 true)
; TAILFOLD-NEXT: [[TMP1:%.*]] = getelementptr i8, ptr [[A]], i64 [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[VP_OP_LOAD:%.*]] = call <vscale x 4 x i8> @llvm.vp.load.nxv4i8.p0(ptr align 1 [[TMP1]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP2:%.*]] = zext <vscale x 4 x i8> [[VP_OP_LOAD]] to <vscale x 4 x i32>
; TAILFOLD-NEXT: [[TMP3:%.*]] = getelementptr i8, ptr [[B]], i64 [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[VP_OP_LOAD1:%.*]] = call <vscale x 4 x i8> @llvm.vp.load.nxv4i8.p0(ptr align 1 [[TMP3]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP4:%.*]] = sext <vscale x 4 x i8> [[VP_OP_LOAD1]] to <vscale x 4 x i32>
; TAILFOLD-NEXT: [[TMP5:%.*]] = mul <vscale x 4 x i32> [[TMP4]], [[TMP2]]
; TAILFOLD-NEXT: [[TMP6:%.*]] = add <vscale x 4 x i32> [[TMP5]], [[VEC_PHI]]
; TAILFOLD-NEXT: [[TMP7]] = call <vscale x 4 x i32> @llvm.vp.merge.nxv4i32(<vscale x 4 x i1> splat (i1 true), <vscale x 4 x i32> [[TMP6]], <vscale x 4 x i32> [[VEC_PHI]], i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP8:%.*]] = zext i32 [[TMP0]] to i64
; TAILFOLD-NEXT: [[INDEX_EVL_NEXT]] = add nuw i64 [[TMP8]], [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[AVL_NEXT]] = sub nuw i64 [[AVL]], [[TMP8]]
; TAILFOLD-NEXT: [[TMP9:%.*]] = icmp eq i64 [[AVL_NEXT]], 0
; TAILFOLD-NEXT: br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
; TAILFOLD: middle.block:
; TAILFOLD-NEXT: [[TMP10:%.*]] = call i32 @llvm.vector.reduce.add.nxv4i32(<vscale x 4 x i32> [[TMP7]])
; TAILFOLD-NEXT: br label [[FOR_EXIT:%.*]]
; TAILFOLD: for.exit:
; TAILFOLD-NEXT: ret i32 [[TMP10]]
;
entry:
br label %for.body

Expand Down Expand Up @@ -632,6 +726,37 @@ define i32 @vqdotsu2(ptr %a, ptr %b) #0 {
; FIXED-ZVQDOTQ: for.exit:
; FIXED-ZVQDOTQ-NEXT: ret i32 [[TMP13]]
;
; TAILFOLD-LABEL: define i32 @vqdotsu2(
; TAILFOLD-SAME: ptr [[A:%.*]], ptr [[B:%.*]]) #[[ATTR0]] {
; TAILFOLD-NEXT: entry:
; TAILFOLD-NEXT: br label [[VECTOR_PH:%.*]]
; TAILFOLD: vector.ph:
; TAILFOLD-NEXT: br label [[VECTOR_BODY:%.*]]
; TAILFOLD: vector.body:
; TAILFOLD-NEXT: [[EVL_BASED_IV:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_EVL_NEXT:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[VEC_PHI:%.*]] = phi <vscale x 4 x i32> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP7:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[AVL:%.*]] = phi i64 [ 1024, [[VECTOR_PH]] ], [ [[AVL_NEXT:%.*]], [[VECTOR_BODY]] ]
; TAILFOLD-NEXT: [[TMP0:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 [[AVL]], i32 4, i1 true)
; TAILFOLD-NEXT: [[TMP1:%.*]] = getelementptr i8, ptr [[A]], i64 [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[VP_OP_LOAD:%.*]] = call <vscale x 4 x i8> @llvm.vp.load.nxv4i8.p0(ptr align 1 [[TMP1]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP2:%.*]] = sext <vscale x 4 x i8> [[VP_OP_LOAD]] to <vscale x 4 x i32>
; TAILFOLD-NEXT: [[TMP3:%.*]] = getelementptr i8, ptr [[B]], i64 [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[VP_OP_LOAD1:%.*]] = call <vscale x 4 x i8> @llvm.vp.load.nxv4i8.p0(ptr align 1 [[TMP3]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP4:%.*]] = zext <vscale x 4 x i8> [[VP_OP_LOAD1]] to <vscale x 4 x i32>
; TAILFOLD-NEXT: [[TMP5:%.*]] = mul <vscale x 4 x i32> [[TMP4]], [[TMP2]]
; TAILFOLD-NEXT: [[TMP6:%.*]] = add <vscale x 4 x i32> [[TMP5]], [[VEC_PHI]]
; TAILFOLD-NEXT: [[TMP7]] = call <vscale x 4 x i32> @llvm.vp.merge.nxv4i32(<vscale x 4 x i1> splat (i1 true), <vscale x 4 x i32> [[TMP6]], <vscale x 4 x i32> [[VEC_PHI]], i32 [[TMP0]])
; TAILFOLD-NEXT: [[TMP8:%.*]] = zext i32 [[TMP0]] to i64
; TAILFOLD-NEXT: [[INDEX_EVL_NEXT]] = add nuw i64 [[TMP8]], [[EVL_BASED_IV]]
; TAILFOLD-NEXT: [[AVL_NEXT]] = sub nuw i64 [[AVL]], [[TMP8]]
; TAILFOLD-NEXT: [[TMP9:%.*]] = icmp eq i64 [[AVL_NEXT]], 0
; TAILFOLD-NEXT: br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP5:![0-9]+]]
; TAILFOLD: middle.block:
; TAILFOLD-NEXT: [[TMP10:%.*]] = call i32 @llvm.vector.reduce.add.nxv4i32(<vscale x 4 x i32> [[TMP7]])
; TAILFOLD-NEXT: br label [[FOR_EXIT:%.*]]
; TAILFOLD: for.exit:
; TAILFOLD-NEXT: ret i32 [[TMP10]]
;
entry:
br label %for.body

Expand Down
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