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[VPlan] Handle live-in extend operands in partial reduction ::computeCost #163175

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[VPlan] Handle live-in extend operands in partial reduction ::computeCost #163175

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[VPlan] Handle live-in extend operands in partial reduction ::compute…
fhahn Oct 13, 2025
26fa3af
!fixup add assertions, use dyn_cast_if_present
fhahn Oct 19, 2025
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16 changes: 11 additions & 5 deletions llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -329,7 +329,12 @@ VPPartialReductionRecipe::computeCost(ElementCount VF,
// recipe.
auto HandleWiden = [&](VPWidenRecipe *Widen) {
if (match(Widen, m_Sub(m_ZeroInt(), m_VPValue(Op)))) {
Widen = dyn_cast<VPWidenRecipe>(Op->getDefiningRecipe());
Widen = dyn_cast<VPWidenRecipe>(Op);
if (!Widen) {
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I left a comment yesterday on @SamTebbs33' patch that took these changes: #147302 (comment)

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Just to clarify what I meant, I don't think there's ever a case where this wouldn't be a WidenRecipe. For the case where Op would be a constant, then -Op would also have been a constant.

It probably makes sense to keep the assert though.

assert(Op->isLiveIn() &&
"Operand must either be a VPWidenRecipe or a live-in");
return;
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What if Op is not a live-in - does it matter? If should never be any other type of recipe, then perhaps worth asserting it's a live-in?

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Currently it must always be a live-in I think. I added an assert for now, thanks

}
}
Opcode = Widen->getOpcode();
VPRecipeBase *ExtAR = Widen->getOperand(0)->getDefiningRecipe();
Expand All @@ -355,14 +360,15 @@ VPPartialReductionRecipe::computeCost(ElementCount VF,
ExtAType = GetExtendKind(OpR);
} else if (isa<VPReductionPHIRecipe>(OpR)) {
auto RedPhiOp1R = getOperand(1)->getDefiningRecipe();
if (isa<VPWidenCastRecipe>(RedPhiOp1R)) {
if (isa_and_nonnull<VPWidenCastRecipe>(RedPhiOp1R)) {
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I left a comment yesterday on @SamTebbs33' patch that took these changes: #147302 (comment)

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I realise I should probably have been a bit clearer here; I don't believe that OpR (which is the chain operand) can ever be nullptr. In contrast, getVecOp() (==getOperand(1)) can be so that should be special cased here, but it may be clearer to write that as:

// The partial.reduce.add's vector operand might not be a live-in.
if (auto *RedPhiOp1R = getVecOp()->getDefiningRecipe()) {
  if (isa<VPWidenCastRecipe>(RedPhiOp1R) {
     ... 
  } else if (auto Widen = dyn_cast<VPWidenRecipe>(RedPhiOp1R))
     ...
}

InputTypeA = Ctx.Types.inferScalarType(RedPhiOp1R->getOperand(0));
ExtAType = GetExtendKind(RedPhiOp1R);
} else if (auto Widen = dyn_cast<VPWidenRecipe>(RedPhiOp1R))
} else if (auto Widen = dyn_cast_if_present<VPWidenRecipe>(RedPhiOp1R))
HandleWiden(Widen);
} else if (auto Widen = dyn_cast<VPWidenRecipe>(OpR)) {
} else if (auto Widen = dyn_cast_if_present<VPWidenRecipe>(OpR)) {
HandleWiden(Widen);
} else if (auto Reduction = dyn_cast<VPPartialReductionRecipe>(OpR)) {
} else if (auto Reduction =
dyn_cast_if_present<VPPartialReductionRecipe>(OpR)) {
return Reduction->computeCost(VF, Ctx);
}
auto *PhiType = Ctx.Types.inferScalarType(getOperand(1));
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58 changes: 58 additions & 0 deletions llvm/test/Transforms/LoopVectorize/AArch64/partial-reduce-constant-ops.ll
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Expand Up @@ -467,3 +467,61 @@ loop:
exit:
ret i32 %red.next
}

; Test case for https://github.com/llvm/llvm-project/issues/162902.
define void @partial_reduction_zext_const(i64 %arg, ptr %ptr) {
; CHECK-LABEL: define void @partial_reduction_zext_const(
; CHECK-SAME: i64 [[ARG:%.*]], ptr [[PTR:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: [[TMP0:%.*]] = sub i64 100, [[ARG]]
; CHECK-NEXT: [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[TMP0]], 4
; CHECK-NEXT: br i1 [[MIN_ITERS_CHECK]], label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: [[N_MOD_VF:%.*]] = urem i64 [[TMP0]], 4
; CHECK-NEXT: [[N_VEC:%.*]] = sub i64 [[TMP0]], [[N_MOD_VF]]
; CHECK-NEXT: [[TMP1:%.*]] = add i64 [[ARG]], [[N_VEC]]
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <4 x i8> [ zeroinitializer, %[[VECTOR_PH]] ], [ [[TMP2:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[TMP2]] = add <4 x i8> [[VEC_PHI]], splat (i8 2)
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
; CHECK-NEXT: [[TMP3:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
; CHECK-NEXT: br i1 [[TMP3]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP16:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[TMP4:%.*]] = call i8 @llvm.vector.reduce.add.v4i8(<4 x i8> [[TMP2]])
; CHECK-NEXT: store i8 [[TMP4]], ptr [[PTR]], align 1
; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[TMP0]], [[N_VEC]]
; CHECK-NEXT: br i1 [[CMP_N]], label %[[EXIT:.*]], label %[[SCALAR_PH]]
; CHECK: [[SCALAR_PH]]:
; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i64 [ [[TMP1]], %[[MIDDLE_BLOCK]] ], [ [[ARG]], %[[ENTRY]] ]
; CHECK-NEXT: [[BC_MERGE_RDX:%.*]] = phi i8 [ [[TMP4]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
; CHECK-NEXT: [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[PARTIAL:%.*]] = phi i8 [ [[BC_MERGE_RDX]], %[[SCALAR_PH]] ], [ [[PARTIAL_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[ZERO_EXT:%.*]] = zext i2 -2 to i8
; CHECK-NEXT: [[PARTIAL_NEXT]] = add i8 [[PARTIAL]], [[ZERO_EXT]]
; CHECK-NEXT: store i8 [[PARTIAL_NEXT]], ptr [[PTR]], align 1
; CHECK-NEXT: [[IV_NEXT]] = add i64 [[IV]], 1
; CHECK-NEXT: [[EC:%.*]] = icmp eq i64 [[IV_NEXT]], 100
; CHECK-NEXT: br i1 [[EC]], label %[[EXIT]], label %[[LOOP]], !llvm.loop [[LOOP17:![0-9]+]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: ret void
;
entry:
br label %loop

loop:
%iv = phi i64 [ %arg, %entry ], [ %iv.next, %loop ]
%partial = phi i8 [ 0, %entry ], [ %partial.next, %loop ]
%zero.ext = zext i2 2 to i8
%partial.next = add i8 %partial, %zero.ext
store i8 %partial.next, ptr %ptr, align 1
%iv.next = add i64 %iv, 1
%ec = icmp eq i64 %iv.next, 100
br i1 %ec, label %exit, label %loop

exit:
ret void
}