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[VPlan] Permit derived IV in isHeaderMask #187360

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Merged
john-brawn-arm merged 2 commits into from
Mar 19, 2026
+6 −5
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[VPlan] Permit derived IV in isHeaderMask #187360

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8b126d4
[VPlan] Permit derived IV in isHeaderMask
john-brawn-arm Mar 18, 2026
7892bfe
Add -vplan-verify-each to mve-reg-pressure-spills.ll
john-brawn-arm Mar 19, 2026
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7 changes: 4 additions & 3 deletions llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
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Expand Up @@ -62,9 +62,10 @@ bool vputils::isHeaderMask(const VPValue *V, const VPlan &Plan) {

VPValue *A, *B;

auto m_CanonicalScalarIVSteps =
m_ScalarIVSteps(m_Specific(Plan.getVectorLoopRegion()->getCanonicalIV()),
m_One(), m_Specific(&Plan.getVF()));
auto m_CanonicalScalarIVSteps = m_ScalarIVSteps(
m_CombineOr(m_CanonicalIV(),
m_DerivedIV(m_ZeroInt(), m_CanonicalIV(), m_One())),
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@fhahn fhahn Mar 18, 2026

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this looks like a missing fold, unless here's a different type?

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@john-brawn-arm john-brawn-arm Mar 19, 2026

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Uses of the DerivedIV do get replaced by the CanonicalIV in the simplifyRecipes vplan pass, and the DerivedIV is then removed in removeDeadRecipes, but the vplan verify failure is happening between it being added (by legalizeAndOptimizeInductions) and removed.

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@fhahn fhahn Mar 19, 2026

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thanks for checking

m_One(), m_Specific(&Plan.getVF()));

if (match(V, m_ActiveLaneMask(m_VPValue(A), m_VPValue(B), m_One())))
return B == Plan.getTripCount() &&
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4 changes: 2 additions & 2 deletions llvm/test/Transforms/LoopVectorize/ARM/mve-reg-pressure-spills.ll
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@@ -1,6 +1,6 @@
; REQUIRES: asserts
; RUN: opt -mcpu=cortex-m55 -passes=loop-vectorize -disable-output -debug-only=loop-vectorize,vplan -vectorizer-consider-reg-pressure=false %s 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-NOPRESSURE
; RUN: opt -mcpu=cortex-m55 -passes=loop-vectorize -disable-output -debug-only=loop-vectorize,vplan -vectorizer-consider-reg-pressure=true %s 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-PRESSURE
; RUN: opt -mcpu=cortex-m55 -passes=loop-vectorize -disable-output -debug-only=loop-vectorize,vplan -vplan-verify-each -vectorizer-consider-reg-pressure=false %s 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-NOPRESSURE
; RUN: opt -mcpu=cortex-m55 -passes=loop-vectorize -disable-output -debug-only=loop-vectorize,vplan -vplan-verify-each -vectorizer-consider-reg-pressure=true %s 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-PRESSURE

target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
target triple = "thumbv8.1m.main-unknown-none-eabihf"
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