[DA] Check for overflow in strong SIV test

Author: 1997alireza

llvm/lib/Analysis/DependenceAnalysis.cpp

@@ -1587,6 +1587,15 @@ static const SCEV *minusSCEVNoSignedOverflow(const SCEV *A, const SCEV *B,
   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 *mulSCEVNoSignedOverflow(const SCEV *A, const SCEV *B,
+                                           ScalarEvolution &SE) {
+  if (SE.willNotOverflow(Instruction::Mul, /*Signed=*/true, A, B))
+    return SE.getMulExpr(A, B);
+  return nullptr;
+}
+
 /// Returns the absolute value of \p A. In the context of dependence analysis,
 /// we need an absolute value in a mathematical sense. If \p A is the signed
 /// minimum value, we cannot represent it unless extending the original type.
@@ -1686,7 +1695,11 @@ bool DependenceInfo::strongSIVtest(const SCEV *Coeff, const SCEV *SrcConst,
   assert(0 < Level && Level <= CommonLevels && "level out of range");
   Level--;
 
-  const SCEV *Delta = SE->getMinusSCEV(SrcConst, DstConst);
+  const SCEV *Delta = minusSCEVNoSignedOverflow(SrcConst, DstConst, *SE);
+  if (!Delta) {
+    Result.Consistent = false;
+    return false;
+  }
   LLVM_DEBUG(dbgs() << "\t    Delta = " << *Delta);
   LLVM_DEBUG(dbgs() << ", " << *Delta->getType() << "\n");
 
@@ -1702,7 +1715,9 @@ bool DependenceInfo::strongSIVtest(const SCEV *Coeff, const SCEV *SrcConst,
     const SCEV *AbsCoeff = absSCEVNoSignedOverflow(Coeff, *SE);
     if (!AbsDelta || !AbsCoeff)
       return false;
-    const SCEV *Product = SE->getMulExpr(UpperBound, AbsCoeff);
+    const SCEV *Product = mulSCEVNoSignedOverflow(UpperBound, AbsCoeff, *SE);
+    if (!Product)
+      return false;
     return isKnownPredicate(CmpInst::ICMP_SGT, AbsDelta, Product);
   }();
   if (IsDeltaLarge) {

llvm/test/Analysis/DependenceAnalysis/SimpleSIVNoValidityCheck.ll

@@ -210,7 +210,7 @@ define void @t3(i64 %n, i64 %m, i64 %lb, ptr %a) {
 ; CHECK-NEXT:  Src: %2 = load i32, ptr %arrayidx6, align 4 --> Dst: %2 = load i32, ptr %arrayidx6, align 4
 ; CHECK-NEXT:    da analyze - none!
 ; CHECK-NEXT:  Src: %2 = load i32, ptr %arrayidx6, align 4 --> Dst: store i32 %2, ptr %arrayidx8, align 4
-; CHECK-NEXT:    da analyze - consistent anti [1 -2]!
+; CHECK-NEXT:    da analyze - anti [1 *]!
 ; CHECK-NEXT:  Src: store i32 %2, ptr %arrayidx8, align 4 --> Dst: store i32 %2, ptr %arrayidx8, align 4
 ; CHECK-NEXT:    da analyze - none!
 ;

llvm/test/Analysis/DependenceAnalysis/StrongSIV.ll

@@ -535,12 +535,16 @@ for.end:                                          ; preds = %for.body
 ;;      if (i < 3000000000)
 ;;        A[i] = 0;
 ;
-; FIXME: DependenceAnalysis currently detects no dependency between A[i] and
-; itself, but it does exist.
+; FIXME: DependenceAnalysis fails to detect the dependency between A[i] and
+; itself, while Strong SIV has been able to prove it.
 define void @strong11(ptr %A) nounwind uwtable ssp {
-; CHECK-LABEL: 'strong11'
-; CHECK-NEXT:  Src: store i32 0, ptr %arrayidx, align 4 --> Dst: store i32 0, ptr %arrayidx, align 4
-; CHECK-NEXT:    da analyze - none!
+; CHECK-ALL-LABEL: 'strong11'
+; CHECK-ALL-NEXT:  Src: store i32 0, ptr %arrayidx, align 4 --> Dst: store i32 0, ptr %arrayidx, align 4
+; CHECK-ALL-NEXT:    da analyze - none!
+;
+; CHECK-STRONG-SIV-LABEL: 'strong11'
+; CHECK-STRONG-SIV-NEXT:  Src: store i32 0, ptr %arrayidx, align 4 --> Dst: store i32 0, ptr %arrayidx, align 4
+; CHECK-STRONG-SIV-NEXT:    da analyze - consistent output [0 S]!
 ;
 entry:
   br label %for.cond1.preheader