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[VPlan] Only compute reg pressure if considered. NFCI #156923

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Merged
merged 2 commits into from
Sep 5, 2025
Merged

[VPlan] Only compute reg pressure if considered. NFCI #156923

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[VPlan] Only compute reg pressure if considered. NFCI
lukel97 Sep 4, 2025
68cd22a
Merge branch 'main' into loop-vectorize/computeRegPressure-only-maxba…
lukel97 Sep 4, 2025
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20 changes: 11 additions & 9 deletions llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -928,8 +928,8 @@ class LoopVectorizationCostModel {
/// user options, for the given register kind.
bool useMaxBandwidth(TargetTransformInfo::RegisterKind RegKind);

/// \return True if register pressure should be calculated for the given VF.
bool shouldCalculateRegPressureForVF(ElementCount VF);
/// \return True if register pressure should be considered for the given VF.
bool shouldConsiderRegPressureForVF(ElementCount VF);

/// \return The size (in bits) of the smallest and widest types in the code
/// that needs to be vectorized. We ignore values that remain scalar such as
Expand Down Expand Up @@ -3700,7 +3700,7 @@ LoopVectorizationCostModel::computeMaxVF(ElementCount UserVF, unsigned UserIC) {
return FixedScalableVFPair::getNone();
}

bool LoopVectorizationCostModel::shouldCalculateRegPressureForVF(
bool LoopVectorizationCostModel::shouldConsiderRegPressureForVF(
ElementCount VF) {
if (!useMaxBandwidth(VF.isScalable()
? TargetTransformInfo::RGK_ScalableVector
Expand Down Expand Up @@ -4147,8 +4147,9 @@ VectorizationFactor LoopVectorizationPlanner::selectVectorizationFactor() {
P->vectorFactors().end());

SmallVector<VPRegisterUsage, 8> RUs;
if (CM.useMaxBandwidth(TargetTransformInfo::RGK_ScalableVector) ||
CM.useMaxBandwidth(TargetTransformInfo::RGK_FixedWidthVector))
if (any_of(VFs, [this](ElementCount VF) {
return CM.shouldConsiderRegPressureForVF(VF);
}))
RUs = calculateRegisterUsageForPlan(*P, VFs, TTI, CM.ValuesToIgnore);

for (unsigned I = 0; I < VFs.size(); I++) {
Expand All @@ -4160,7 +4161,7 @@ VectorizationFactor LoopVectorizationPlanner::selectVectorizationFactor() {
/// If the register pressure needs to be considered for VF,
/// don't consider the VF as valid if it exceeds the number
/// of registers for the target.
if (CM.shouldCalculateRegPressureForVF(VF) &&
if (CM.shouldConsiderRegPressureForVF(VF) &&
RUs[I].exceedsMaxNumRegs(TTI, ForceTargetNumVectorRegs))
continue;

Expand Down Expand Up @@ -6996,8 +6997,9 @@ VectorizationFactor LoopVectorizationPlanner::computeBestVF() {
P->vectorFactors().end());

SmallVector<VPRegisterUsage, 8> RUs;
if (CM.useMaxBandwidth(TargetTransformInfo::RGK_ScalableVector) ||
CM.useMaxBandwidth(TargetTransformInfo::RGK_FixedWidthVector))
if (any_of(VFs, [this](ElementCount VF) {
return CM.shouldConsiderRegPressureForVF(VF);
}))
RUs = calculateRegisterUsageForPlan(*P, VFs, TTI, CM.ValuesToIgnore);

for (unsigned I = 0; I < VFs.size(); I++) {
Expand All @@ -7023,7 +7025,7 @@ VectorizationFactor LoopVectorizationPlanner::computeBestVF() {
InstructionCost Cost = cost(*P, VF);
VectorizationFactor CurrentFactor(VF, Cost, ScalarCost);

if (CM.shouldCalculateRegPressureForVF(VF) &&
if (CM.shouldConsiderRegPressureForVF(VF) &&
RUs[I].exceedsMaxNumRegs(TTI, ForceTargetNumVectorRegs)) {
LLVM_DEBUG(dbgs() << "LV(REG): Not considering vector loop of width "
<< VF << " because it uses too many registers\n");
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/LoopVectorize/AArch64/reg-usage.ll
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Expand Up @@ -14,7 +14,7 @@

define void @get_invariant_reg_usage(ptr %z) {
; CHECK-LABEL: LV: Checking a loop in 'get_invariant_reg_usage'
; CHECK: LV(REG): VF = vscale x 16
; CHECK: LV(REG): VF = 16
; CHECK-NEXT: LV(REG): Found max usage: 2 item
; CHECK-NEXT: LV(REG): RegisterClass: Generic::ScalarRC, 2 registers
; CHECK-NEXT: LV(REG): RegisterClass: Generic::VectorRC, 1 registers
Expand Down