[DA] Widening SCEV expressions in strong SIV test to prevent overflow

By doubling the size of the expressions in the strong SIV test, no
overflow occurs in the multiplication required to check the test.

Author: 1997alireza

llvm/lib/Analysis/DependenceAnalysis.cpp

@@ -1668,17 +1668,35 @@ bool DependenceInfo::strongSIVtest(const SCEV *Coeff, const SCEV *SrcConst,
   LLVM_DEBUG(dbgs() << "\t    Delta = " << *Delta);
   LLVM_DEBUG(dbgs() << ", " << *Delta->getType() << "\n");
 
+  TypeSize CoeffSize =
+      Coeff->getType()->getScalarType()->getPrimitiveSizeInBits();
+  TypeSize SrcSize =
+      SrcConst->getType()->getScalarType()->getPrimitiveSizeInBits();
+  TypeSize DstSize =
+      DstConst->getType()->getScalarType()->getPrimitiveSizeInBits();
+  TypeSize WideSize = std::max(CoeffSize, std::max(SrcSize, DstSize)) * 2;
+  LLVMContext &Context = CurDstLoop->getHeader()->getParent()->getContext();
+  Type *WideTy = IntegerType::get(Context, WideSize);
+  const SCEV *WideSrcC = SE->getSignExtendExpr(SrcConst, WideTy);
+  const SCEV *WideDstC = SE->getSignExtendExpr(DstConst, WideTy);
+  const SCEV *WideDelta = SE->getMinusSCEV(WideSrcC, WideDstC);
+  const SCEV *WideCoeff = SE->getSignExtendExpr(Coeff, WideTy);
+
   // check that |Delta| < iteration count
-  if (const SCEV *UpperBound =
-          collectUpperBound(CurSrcLoop, Delta->getType())) {
-    LLVM_DEBUG(dbgs() << "\t    UpperBound = " << *UpperBound);
-    LLVM_DEBUG(dbgs() << ", " << *UpperBound->getType() << "\n");
-    const SCEV *AbsDelta =
-        SE->isKnownNonNegative(Delta) ? Delta : SE->getNegativeSCEV(Delta);
-    const SCEV *AbsCoeff =
-        SE->isKnownNonNegative(Coeff) ? Coeff : SE->getNegativeSCEV(Coeff);
-    const SCEV *Product = SE->getMulExpr(UpperBound, AbsCoeff);
-    if (isKnownPredicate(CmpInst::ICMP_SGT, AbsDelta, Product)) {
+  if (const SCEV *WideUpperBound =
+          collectUpperBound(CurSrcLoop, WideDelta->getType())) {
+    LLVM_DEBUG(dbgs() << "\t    WideUpperBound = " << *WideUpperBound);
+    LLVM_DEBUG(dbgs() << ", " << *WideUpperBound->getType() << "\n");
+
+    // FIXME: Use SCEV getAbsExpr function to compute the abstract values
+    const SCEV *WideAbsDelta = SE->isKnownNonNegative(WideDelta)
+                                   ? WideDelta
+                                   : SE->getNegativeSCEV(WideDelta);
+    const SCEV *WideAbsCoeff = SE->isKnownNonNegative(WideCoeff)
+                                   ? WideCoeff
+                                   : SE->getNegativeSCEV(WideCoeff);
+    const SCEV *WideProduct = SE->getMulExpr(WideUpperBound, WideAbsCoeff);
+    if (isKnownPredicate(CmpInst::ICMP_SGT, WideAbsDelta, WideProduct)) {
       // Distance greater than trip count - no dependence
       ++StrongSIVindependence;
       ++StrongSIVsuccesses;