[llvm-branch-commits] [llvm] [DA] Add overflow check in ExactSIV (PR #157086)

[Ryotaro Kasuga via llvm-branch-commits]

https://github.com/kasuga-fj updated 
https://github.com/llvm/llvm-project/pull/157086

>From 7678c02d942a548219bbe66cb425a1482b7d9924 Mon Sep 17 00:00:00 2001
From: Ryotaro Kasuga <kasuga.ryot...@fujitsu.com>
Date: Fri, 5 Sep 2025 11:41:29 +0000
Subject: [PATCH] [DA] Add overflow check in ExactSIV

---
 llvm/lib/Analysis/DependenceAnalysis.cpp          | 14 +++++++++++++-
 llvm/test/Analysis/DependenceAnalysis/ExactSIV.ll |  2 +-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp 
b/llvm/lib/Analysis/DependenceAnalysis.cpp
index 0f77a1410e83b..6e576e866b310 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -1170,6 +1170,15 @@ const SCEVConstant 
*DependenceInfo::collectConstantUpperBound(const Loop *L,
   return nullptr;
 }
 
+/// Returns \p A - \p B if it guaranteed not to signed wrap. Otherwise returns
+/// nullptr. \p A and \p B must have the same integer type.
+static const SCEV *minusSCEVNoSignedOverflow(const SCEV *A, const SCEV *B,
+                                             ScalarEvolution &SE) {
+  if (SE.willNotOverflow(Instruction::Sub, /*Signed=*/true, A, B))
+    return SE.getMinusSCEV(A, B);
+  return nullptr;
+}
+
 // testZIV -
 // When we have a pair of subscripts of the form [c1] and [c2],
 // where c1 and c2 are both loop invariant, we attack it using
@@ -1626,7 +1635,9 @@ bool DependenceInfo::exactSIVtest(const SCEV *SrcCoeff, 
const SCEV *DstCoeff,
   assert(0 < Level && Level <= CommonLevels && "Level out of range");
   Level--;
   Result.Consistent = false;
-  const SCEV *Delta = SE->getMinusSCEV(DstConst, SrcConst);
+  const SCEV *Delta = minusSCEVNoSignedOverflow(DstConst, SrcConst, *SE);
+  if (!Delta)
+    return false;
   LLVM_DEBUG(dbgs() << "\t    Delta = " << *Delta << "\n");
   NewConstraint.setLine(SrcCoeff, SE->getNegativeSCEV(DstCoeff), Delta,
                         CurLoop);
@@ -1716,6 +1727,7 @@ bool DependenceInfo::exactSIVtest(const SCEV *SrcCoeff, 
const SCEV *DstCoeff,
   // explore directions
   unsigned NewDirection = Dependence::DVEntry::NONE;
   APInt LowerDistance, UpperDistance;
+  // TODO: Overflow check may be needed.
   if (TA.sgt(TB)) {
     LowerDistance = (TY - TX) + (TA - TB) * TL;
     UpperDistance = (TY - TX) + (TA - TB) * TU;
diff --git a/llvm/test/Analysis/DependenceAnalysis/ExactSIV.ll 
b/llvm/test/Analysis/DependenceAnalysis/ExactSIV.ll
index 2ee234f270e6d..54166bf5e8a17 100644
--- a/llvm/test/Analysis/DependenceAnalysis/ExactSIV.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/ExactSIV.ll
@@ -834,7 +834,7 @@ define void @exact14(ptr %A) {
 ; CHECK-SIV-ONLY-NEXT:  Src: store i8 0, ptr %idx.0, align 1 --> Dst: store i8 
0, ptr %idx.0, align 1
 ; CHECK-SIV-ONLY-NEXT:    da analyze - none!
 ; CHECK-SIV-ONLY-NEXT:  Src: store i8 0, ptr %idx.0, align 1 --> Dst: store i8 
1, ptr %idx.1, align 1
-; CHECK-SIV-ONLY-NEXT:    da analyze - none!
+; CHECK-SIV-ONLY-NEXT:    da analyze - output [*|<]!
 ; CHECK-SIV-ONLY-NEXT:  Src: store i8 1, ptr %idx.1, align 1 --> Dst: store i8 
1, ptr %idx.1, align 1
 ; CHECK-SIV-ONLY-NEXT:    da analyze - none!
 ;

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