[llvm] [DA] Rewrite BanerjeeMIV test with safe APInt interval arithmetic (PR #207662)

[Ryotaro Kasuga via llvm-commits]

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@@ -1922,36 +1922,167 @@ bool DependenceInfo::gcdMIVtest(const SCEV *Src, const SCEV *Dst,
 }
 
 //===----------------------------------------------------------------------===//
+
+namespace {
+struct BanerjeeInterval {
+  std::optional<APInt> Lower;
+  std::optional<APInt> Upper;
+
+  BanerjeeInterval(std::optional<APInt> Lower, std::optional<APInt> Upper)
+      : Lower(std::move(Lower)), Upper(std::move(Upper)) {}
+};
+} // namespace
+
+static APInt signedMin(const APInt &A, const APInt &B) {
+  return A.slt(B) ? A : B;
+}
+
+static APInt signedMax(const APInt &A, const APInt &B) {
+  return A.sgt(B) ? A : B;
+}
+
+static BanerjeeInterval addIntervals(const BanerjeeInterval &A,
+                                     const BanerjeeInterval &B) {
+  std::optional<APInt> Lower;
+  std::optional<APInt> Upper;
+  if (A.Lower && B.Lower)
+    Lower = *A.Lower + *B.Lower;
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kasuga-fj wrote:

What happens if this addition overflows? Same applies to all other APInt arithmetics.

https://github.com/llvm/llvm-project/pull/207662