[llvm-branch-commits] [llvm] [DA] Rewrite formula in the Weak Zero SIV tests (PR #183738)
Ryotaro Kasuga via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Sun Mar 1 23:42:47 PST 2026
https://github.com/kasuga-fj updated https://github.com/llvm/llvm-project/pull/183738
>From 65e8bf68b51636c834238b5001cf61832376c14a Mon Sep 17 00:00:00 2001
From: Ryotaro Kasuga <kasuga.ryotaro at fujitsu.com>
Date: Fri, 27 Feb 2026 12:53:35 +0000
Subject: [PATCH] [DA] Rewrite formula in the Weak Zero SIV tests
---
.../llvm/Analysis/DependenceAnalysis.h | 12 +-
llvm/lib/Analysis/DependenceAnalysis.cpp | 139 +++++++++---------
.../weak-crossing-siv-large-btc.ll | 4 +-
.../weak-zero-siv-large-btc.ll | 8 +-
.../weak-zero-siv-overflow.ll | 8 +-
5 files changed, 79 insertions(+), 92 deletions(-)
diff --git a/llvm/include/llvm/Analysis/DependenceAnalysis.h b/llvm/include/llvm/Analysis/DependenceAnalysis.h
index b99b2f5960049..25954a2535df3 100644
--- a/llvm/include/llvm/Analysis/DependenceAnalysis.h
+++ b/llvm/include/llvm/Analysis/DependenceAnalysis.h
@@ -570,10 +570,8 @@ class DependenceInfo {
/// Sets appropriate direction entry.
/// Set consistent to false.
/// If loop peeling will break the dependence, mark appropriately.
- bool weakZeroSrcSIVtest(const SCEV *DstCoeff, const SCEV *SrcConst,
- const SCEV *DstConst, const Loop *CurrentSrcLoop,
- const Loop *CurrentDstLoop, unsigned Level,
- FullDependence &Result) const;
+ bool weakZeroSrcSIVtest(const SCEV *SrcConst, const SCEVAddRecExpr *Dst,
+ unsigned Level, FullDependence &Result) const;
/// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair
/// (Src and Dst) for dependence.
@@ -585,10 +583,8 @@ class DependenceInfo {
/// Sets appropriate direction entry.
/// Set consistent to false.
/// If loop peeling will break the dependence, mark appropriately.
- bool weakZeroDstSIVtest(const SCEV *SrcCoeff, const SCEV *SrcConst,
- const SCEV *DstConst, const Loop *CurrentSrcLoop,
- const Loop *CurrentDstLoop, unsigned Level,
- FullDependence &Result) const;
+ bool weakZeroDstSIVtest(const SCEVAddRecExpr *Src, const SCEV *DstConst,
+ unsigned Level, FullDependence &Result) const;
/// exactRDIVtest - Tests the RDIV subscript pair for dependence.
/// Things of the form [c1 + a*i] and [c2 + b*j],
diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index b9be42e5ad792..67444933579cb 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -1789,6 +1789,19 @@ static bool isRemainderZero(const SCEVConstant *Dividend,
return ConstDividend.srem(ConstDivisor) == 0;
}
+/// An auxiliary function for the Weak-Zero SIV test. Return true if \p AR
+/// overlaps with \p Const iff at the last iteration of the loop, where \p AR is
+/// an affine AddRec expression, \p Const is a loop invariant constant, and \p
+/// UpperBound is the exact backedge-taken count of the loop.
+static bool isOverlapLastWeakZeroSIV(const SCEVAddRecExpr *AR,
+ const SCEV *Const, ScalarEvolution &SE,
+ const SCEV *UpperBound) {
+ return AR->hasNoSignedWrap() &&
+ SE.isKnownNonZero(AR->getStepRecurrence(SE)) &&
+ SE.isKnownPredicate(CmpInst::ICMP_EQ,
+ AR->evaluateAtIteration(UpperBound, SE), Const);
+}
+
// weakZeroSrcSIVtest -
// From the paper, Practical Dependence Testing, Section 4.2.2
//
@@ -1820,11 +1833,9 @@ static bool isRemainderZero(const SCEVConstant *Dividend,
// (see also weakZeroDstSIVtest)
//
// Return true if dependence disproved.
-bool DependenceInfo::weakZeroSrcSIVtest(const SCEV *DstCoeff,
- const SCEV *SrcConst,
- const SCEV *DstConst,
- const Loop *CurSrcLoop,
- const Loop *CurDstLoop, unsigned Level,
+bool DependenceInfo::weakZeroSrcSIVtest(const SCEV *SrcConst,
+ const SCEVAddRecExpr *Dst,
+ unsigned Level,
FullDependence &Result) const {
if (!isDependenceTestEnabled(DependenceTestType::WeakZeroSIV))
return false;
@@ -1832,6 +1843,8 @@ bool DependenceInfo::weakZeroSrcSIVtest(const SCEV *DstCoeff,
// For the WeakSIV test, it's possible the loop isn't common to
// the Src and Dst loops. If it isn't, then there's no need to
// record a direction.
+ const SCEV *DstCoeff = Dst->getStepRecurrence(*SE);
+ const SCEV *DstConst = Dst->getStart();
LLVM_DEBUG(dbgs() << "\tWeak-Zero (src) SIV test\n");
LLVM_DEBUG(dbgs() << "\t DstCoeff = " << *DstCoeff << "\n");
LLVM_DEBUG(dbgs() << "\t SrcConst = " << *SrcConst << "\n");
@@ -1840,6 +1853,27 @@ bool DependenceInfo::weakZeroSrcSIVtest(const SCEV *DstCoeff,
assert(0 < Level && Level <= MaxLevels && "Level out of range");
Level--;
Result.Consistent = false;
+
+ ConstantRange SrcRange = SE->getSignedRange(SrcConst);
+ ConstantRange DstRange = SE->getSignedRange(Dst);
+ if (SrcRange.intersectWith(DstRange).isEmptySet()) {
+ ++WeakZeroSIVindependence;
+ ++WeakZeroSIVsuccesses;
+ return true;
+ }
+ if (const SCEV *UpperBound =
+ collectUpperBound(Dst->getLoop(), Dst->getType())) {
+ bool OverlapAtLast =
+ isOverlapLastWeakZeroSIV(Dst, SrcConst, *SE, UpperBound);
+ if (OverlapAtLast) {
+ if (Level < CommonLevels) {
+ Result.DV[Level].Direction &= Dependence::DVEntry::LE;
+ ++WeakZeroSIVsuccesses;
+ }
+ return false;
+ }
+ }
+
const SCEV *Delta = SE->getMinusSCEV(SrcConst, DstConst);
LLVM_DEBUG(dbgs() << "\t Delta = " << *Delta << "\n");
if (SE->isKnownPredicate(CmpInst::ICMP_EQ, SrcConst, DstConst) &&
@@ -1850,39 +1884,14 @@ bool DependenceInfo::weakZeroSrcSIVtest(const SCEV *DstCoeff,
}
return false; // dependences caused by first iteration
}
+
const SCEVConstant *ConstCoeff = dyn_cast<SCEVConstant>(DstCoeff);
if (!ConstCoeff)
return false;
- // Since ConstCoeff is constant, !isKnownNegative means it's non-negative.
- // TODO: Bail out if it's a signed minimum value.
- const SCEV *AbsCoeff = SE->isKnownNegative(ConstCoeff)
- ? SE->getNegativeSCEV(ConstCoeff)
- : ConstCoeff;
const SCEV *NewDelta =
SE->isKnownNegative(ConstCoeff) ? SE->getNegativeSCEV(Delta) : Delta;
- // check that Delta/SrcCoeff < iteration count
- // really check NewDelta < count*AbsCoeff
- if (const SCEV *UpperBound =
- collectUpperBound(CurSrcLoop, Delta->getType())) {
- LLVM_DEBUG(dbgs() << "\t UpperBound = " << *UpperBound << "\n");
- const SCEV *Product = SE->getMulExpr(AbsCoeff, UpperBound);
- if (SE->isKnownPredicate(CmpInst::ICMP_SGT, NewDelta, Product)) {
- ++WeakZeroSIVindependence;
- ++WeakZeroSIVsuccesses;
- return true;
- }
- if (SE->isKnownPredicate(CmpInst::ICMP_EQ, NewDelta, Product)) {
- // dependences caused by last iteration
- if (Level < CommonLevels) {
- Result.DV[Level].Direction &= Dependence::DVEntry::LE;
- ++WeakZeroSIVsuccesses;
- }
- return false;
- }
- }
-
// check that Delta/SrcCoeff >= 0
// really check that NewDelta >= 0
if (SE->isKnownNegative(NewDelta)) {
@@ -1933,17 +1942,16 @@ bool DependenceInfo::weakZeroSrcSIVtest(const SCEV *DstCoeff,
// (see also weakZeroSrcSIVtest)
//
// Return true if dependence disproved.
-bool DependenceInfo::weakZeroDstSIVtest(const SCEV *SrcCoeff,
- const SCEV *SrcConst,
- const SCEV *DstConst,
- const Loop *CurSrcLoop,
- const Loop *CurDstLoop, unsigned Level,
+bool DependenceInfo::weakZeroDstSIVtest(const SCEVAddRecExpr *Src,
+ const SCEV *DstConst, unsigned Level,
FullDependence &Result) const {
if (!isDependenceTestEnabled(DependenceTestType::WeakZeroSIV))
return false;
// For the WeakSIV test, it's possible the loop isn't common to the
// Src and Dst loops. If it isn't, then there's no need to record a direction.
+ const SCEV *SrcCoeff = Src->getStepRecurrence(*SE);
+ const SCEV *SrcConst = Src->getStart();
LLVM_DEBUG(dbgs() << "\tWeak-Zero (dst) SIV test\n");
LLVM_DEBUG(dbgs() << "\t SrcCoeff = " << *SrcCoeff << "\n");
LLVM_DEBUG(dbgs() << "\t SrcConst = " << *SrcConst << "\n");
@@ -1952,6 +1960,27 @@ bool DependenceInfo::weakZeroDstSIVtest(const SCEV *SrcCoeff,
assert(0 < Level && Level <= SrcLevels && "Level out of range");
Level--;
Result.Consistent = false;
+
+ ConstantRange SrcRange = SE->getSignedRange(Src);
+ ConstantRange DstRange = SE->getSignedRange(DstConst);
+ if (SrcRange.intersectWith(DstRange).isEmptySet()) {
+ ++WeakZeroSIVindependence;
+ ++WeakZeroSIVsuccesses;
+ return true;
+ }
+ if (const SCEV *UpperBound =
+ collectUpperBound(Src->getLoop(), Src->getType())) {
+ bool OverlapAtLast =
+ isOverlapLastWeakZeroSIV(Src, DstConst, *SE, UpperBound);
+ if (OverlapAtLast) {
+ if (Level < CommonLevels) {
+ Result.DV[Level].Direction &= Dependence::DVEntry::GE;
+ ++WeakZeroSIVsuccesses;
+ }
+ return false;
+ }
+ }
+
const SCEV *Delta = SE->getMinusSCEV(DstConst, SrcConst);
LLVM_DEBUG(dbgs() << "\t Delta = " << *Delta << "\n");
if (SE->isKnownPredicate(CmpInst::ICMP_EQ, DstConst, SrcConst) &&
@@ -1966,35 +1995,9 @@ bool DependenceInfo::weakZeroDstSIVtest(const SCEV *SrcCoeff,
if (!ConstCoeff)
return false;
- // Since ConstCoeff is constant, !isKnownNegative means it's non-negative.
- // TODO: Bail out if it's a signed minimum value.
- const SCEV *AbsCoeff = SE->isKnownNegative(ConstCoeff)
- ? SE->getNegativeSCEV(ConstCoeff)
- : ConstCoeff;
const SCEV *NewDelta =
SE->isKnownNegative(ConstCoeff) ? SE->getNegativeSCEV(Delta) : Delta;
- // check that Delta/SrcCoeff < iteration count
- // really check NewDelta < count*AbsCoeff
- if (const SCEV *UpperBound =
- collectUpperBound(CurSrcLoop, Delta->getType())) {
- LLVM_DEBUG(dbgs() << "\t UpperBound = " << *UpperBound << "\n");
- const SCEV *Product = SE->getMulExpr(AbsCoeff, UpperBound);
- if (SE->isKnownPredicate(CmpInst::ICMP_SGT, NewDelta, Product)) {
- ++WeakZeroSIVindependence;
- ++WeakZeroSIVsuccesses;
- return true;
- }
- if (SE->isKnownPredicate(CmpInst::ICMP_EQ, NewDelta, Product)) {
- // dependences caused by last iteration
- if (Level < CommonLevels) {
- Result.DV[Level].Direction &= Dependence::DVEntry::GE;
- ++WeakZeroSIVsuccesses;
- }
- return false;
- }
- }
-
// check that Delta/SrcCoeff >= 0
// really check that NewDelta >= 0
if (SE->isKnownNegative(NewDelta)) {
@@ -2315,23 +2318,15 @@ bool DependenceInfo::testSIV(const SCEV *Src, const SCEV *Dst, unsigned &Level,
CurDstLoop);
}
if (SrcAddRec) {
- const SCEV *SrcConst = SrcAddRec->getStart();
- const SCEV *SrcCoeff = SrcAddRec->getStepRecurrence(*SE);
- const SCEV *DstConst = Dst;
const Loop *CurSrcLoop = SrcAddRec->getLoop();
Level = mapSrcLoop(CurSrcLoop);
- return weakZeroDstSIVtest(SrcCoeff, SrcConst, DstConst, CurSrcLoop,
- CurSrcLoop, Level, Result) ||
+ return weakZeroDstSIVtest(SrcAddRec, Dst, Level, Result) ||
gcdMIVtest(Src, Dst, Result);
}
if (DstAddRec) {
- const SCEV *DstConst = DstAddRec->getStart();
- const SCEV *DstCoeff = DstAddRec->getStepRecurrence(*SE);
- const SCEV *SrcConst = Src;
const Loop *CurDstLoop = DstAddRec->getLoop();
Level = mapDstLoop(CurDstLoop);
- return weakZeroSrcSIVtest(DstCoeff, SrcConst, DstConst, CurDstLoop,
- CurDstLoop, Level, Result) ||
+ return weakZeroSrcSIVtest(Src, DstAddRec, Level, Result) ||
gcdMIVtest(Src, Dst, Result);
}
llvm_unreachable("SIV test expected at least one AddRec");
diff --git a/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-large-btc.ll b/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-large-btc.ll
index b097c06e31202..d85ce2d9eea63 100644
--- a/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-large-btc.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-large-btc.ll
@@ -13,8 +13,8 @@
; A[i1] = 0;
; }
;
-; FIXME: Both `A[i0] = 0` and `A[i1] = 0` must be executed, so there is a
-; dependency between them.
+; Both `A[i0] = 0` and `A[i1] = 0` must be executed, so there is a dependency
+; between them.
;
define void @weak_crossing_siv_large_btc(ptr %A) {
; CHECK-ALL-LABEL: 'weak_crossing_siv_large_btc'
diff --git a/llvm/test/Analysis/DependenceAnalysis/weak-zero-siv-large-btc.ll b/llvm/test/Analysis/DependenceAnalysis/weak-zero-siv-large-btc.ll
index c06032798c792..eb1000b053255 100644
--- a/llvm/test/Analysis/DependenceAnalysis/weak-zero-siv-large-btc.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/weak-zero-siv-large-btc.ll
@@ -18,7 +18,7 @@ define void @weak_zero_src_siv_large_btc(ptr %A) {
; CHECK-ALL-NEXT: Src: store i8 0, ptr %gep, align 1 --> Dst: store i8 0, ptr %gep, align 1
; CHECK-ALL-NEXT: da analyze - none!
; CHECK-ALL-NEXT: Src: store i8 0, ptr %gep, align 1 --> Dst: store i8 1, ptr %A, align 1
-; CHECK-ALL-NEXT: da analyze - none!
+; CHECK-ALL-NEXT: da analyze - output [*|<]!
; CHECK-ALL-NEXT: Src: store i8 1, ptr %A, align 1 --> Dst: store i8 1, ptr %A, align 1
; CHECK-ALL-NEXT: da analyze - consistent output [S]!
;
@@ -26,7 +26,7 @@ define void @weak_zero_src_siv_large_btc(ptr %A) {
; CHECK-WEAK-ZERO-SRC-SIV-NEXT: Src: store i8 0, ptr %gep, align 1 --> Dst: store i8 0, ptr %gep, align 1
; CHECK-WEAK-ZERO-SRC-SIV-NEXT: da analyze - consistent output [*]!
; CHECK-WEAK-ZERO-SRC-SIV-NEXT: Src: store i8 0, ptr %gep, align 1 --> Dst: store i8 1, ptr %A, align 1
-; CHECK-WEAK-ZERO-SRC-SIV-NEXT: da analyze - none!
+; CHECK-WEAK-ZERO-SRC-SIV-NEXT: da analyze - output [*|<]!
; CHECK-WEAK-ZERO-SRC-SIV-NEXT: Src: store i8 1, ptr %A, align 1 --> Dst: store i8 1, ptr %A, align 1
; CHECK-WEAK-ZERO-SRC-SIV-NEXT: da analyze - consistent output [S]!
;
@@ -68,7 +68,7 @@ define void @weak_zero_dst_siv_large_btc(ptr %A) {
; CHECK-ALL-NEXT: Src: store i8 1, ptr %A, align 1 --> Dst: store i8 1, ptr %A, align 1
; CHECK-ALL-NEXT: da analyze - consistent output [S]!
; CHECK-ALL-NEXT: Src: store i8 1, ptr %A, align 1 --> Dst: store i8 0, ptr %gep, align 1
-; CHECK-ALL-NEXT: da analyze - none!
+; CHECK-ALL-NEXT: da analyze - output [*|<]!
; CHECK-ALL-NEXT: Src: store i8 0, ptr %gep, align 1 --> Dst: store i8 0, ptr %gep, align 1
; CHECK-ALL-NEXT: da analyze - none!
;
@@ -76,7 +76,7 @@ define void @weak_zero_dst_siv_large_btc(ptr %A) {
; CHECK-WEAK-ZERO-SRC-SIV-NEXT: Src: store i8 1, ptr %A, align 1 --> Dst: store i8 1, ptr %A, align 1
; CHECK-WEAK-ZERO-SRC-SIV-NEXT: da analyze - consistent output [S]!
; CHECK-WEAK-ZERO-SRC-SIV-NEXT: Src: store i8 1, ptr %A, align 1 --> Dst: store i8 0, ptr %gep, align 1
-; CHECK-WEAK-ZERO-SRC-SIV-NEXT: da analyze - none!
+; CHECK-WEAK-ZERO-SRC-SIV-NEXT: da analyze - output [*|<]!
; CHECK-WEAK-ZERO-SRC-SIV-NEXT: Src: store i8 0, ptr %gep, align 1 --> Dst: store i8 0, ptr %gep, align 1
; CHECK-WEAK-ZERO-SRC-SIV-NEXT: da analyze - consistent output [*]!
;
diff --git a/llvm/test/Analysis/DependenceAnalysis/weak-zero-siv-overflow.ll b/llvm/test/Analysis/DependenceAnalysis/weak-zero-siv-overflow.ll
index 6317c387858d3..7ce0ef32100cf 100644
--- a/llvm/test/Analysis/DependenceAnalysis/weak-zero-siv-overflow.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/weak-zero-siv-overflow.ll
@@ -10,16 +10,12 @@
; A[2] = 2;
; }
;
-; FIXME: DependenceAnalysis currently detects no dependency between the two
-; stores, but it does exist. The root cause is that the product of the BTC and
-; the coefficient ((1LL << 62) - 1 and 2) overflows in a signed sense.
-;
define void @weakzero_dst_siv_prod_ovfl(ptr %A) {
; CHECK-ALL-LABEL: 'weakzero_dst_siv_prod_ovfl'
; CHECK-ALL-NEXT: Src: store i8 1, ptr %gep.0, align 1 --> Dst: store i8 1, ptr %gep.0, align 1
; CHECK-ALL-NEXT: da analyze - none!
; CHECK-ALL-NEXT: Src: store i8 1, ptr %gep.0, align 1 --> Dst: store i8 2, ptr %gep.1, align 1
-; CHECK-ALL-NEXT: da analyze - none!
+; CHECK-ALL-NEXT: da analyze - output [*|<]!
; CHECK-ALL-NEXT: Src: store i8 2, ptr %gep.1, align 1 --> Dst: store i8 2, ptr %gep.1, align 1
; CHECK-ALL-NEXT: da analyze - consistent output [S]!
;
@@ -27,7 +23,7 @@ define void @weakzero_dst_siv_prod_ovfl(ptr %A) {
; CHECK-WEAK-ZERO-SIV-NEXT: Src: store i8 1, ptr %gep.0, align 1 --> Dst: store i8 1, ptr %gep.0, align 1
; CHECK-WEAK-ZERO-SIV-NEXT: da analyze - consistent output [*]!
; CHECK-WEAK-ZERO-SIV-NEXT: Src: store i8 1, ptr %gep.0, align 1 --> Dst: store i8 2, ptr %gep.1, align 1
-; CHECK-WEAK-ZERO-SIV-NEXT: da analyze - none!
+; CHECK-WEAK-ZERO-SIV-NEXT: da analyze - output [*|<]!
; CHECK-WEAK-ZERO-SIV-NEXT: Src: store i8 2, ptr %gep.1, align 1 --> Dst: store i8 2, ptr %gep.1, align 1
; CHECK-WEAK-ZERO-SIV-NEXT: da analyze - consistent output [S]!
;
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