SCEV: thread samesign in isBasicBlockEntryGuardedByCond (NFC) (#125840)

isBasicBlockEntryGuardedByCond inadvertedenly drops samesign information
when calling ICmpInst::getNonStrictPredicate. Fix this.

Author: artagnon

llvm/include/llvm/IR/Instructions.h

@@ -1231,6 +1231,18 @@ class ICmpInst: public CmpInst {
     return getSwappedCmpPredicate(getCmpPredicate());
   }
 
+  /// @returns the non-strict predicate along with samesign information: static
+  /// variant.
+  static CmpPredicate getNonStrictCmpPredicate(CmpPredicate Pred) {
+    return {getNonStrictPredicate(Pred), Pred.hasSameSign()};
+  }
+
+  /// For example, SGT -> SGE, SLT -> SLE, ULT -> ULE, UGT -> UGE.
+  /// @returns the non-strict predicate along with samesign information.
+  Predicate getNonStrictCmpPredicate() const {
+    return getNonStrictCmpPredicate(getCmpPredicate());
+  }
+
   /// For example, EQ->EQ, SLE->SLE, UGT->SGT, etc.
   /// @returns the predicate that would be the result if the operand were
   /// regarded as signed.

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -11632,8 +11632,9 @@ bool ScalarEvolution::isBasicBlockEntryGuardedByCond(const BasicBlock *BB,
   // non-strict comparison is known from ranges and non-equality is known from
   // dominating predicates. If we are proving strict comparison, we always try
   // to prove non-equality and non-strict comparison separately.
-  auto NonStrictPredicate = ICmpInst::getNonStrictPredicate(Pred);
-  const bool ProvingStrictComparison = (Pred != NonStrictPredicate);
+  CmpPredicate NonStrictPredicate = ICmpInst::getNonStrictCmpPredicate(Pred);
+  const bool ProvingStrictComparison =
+      (Pred != static_cast<CmpInst::Predicate>(NonStrictPredicate));
   bool ProvedNonStrictComparison = false;
   bool ProvedNonEquality = false;