[IR] Add helper CmpPredicate::dropSameSign (#134071)

Address review comment
#133711 (comment)

Author: dtcxzyw

llvm/include/llvm/IR/CmpPredicate.h

@@ -41,6 +41,10 @@ class CmpPredicate {
   /// Query samesign information, for optimizations.
   bool hasSameSign() const { return HasSameSign; }
 
+  /// Drops samesign information. This is used when the samesign information
+  /// should be dropped explicitly.
+  CmpInst::Predicate dropSameSign() const { return Pred; }
+
   /// Compares two CmpPredicates taking samesign into account and returns the
   /// canonicalized CmpPredicate if they match. An alternative to operator==.
   ///

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -11622,7 +11622,7 @@ bool ScalarEvolution::isBasicBlockEntryGuardedByCond(const BasicBlock *BB,
   // to prove non-equality and non-strict comparison separately.
   CmpPredicate NonStrictPredicate = ICmpInst::getNonStrictCmpPredicate(Pred);
   const bool ProvingStrictComparison =
-      (Pred != static_cast<CmpInst::Predicate>(NonStrictPredicate));
+      Pred != NonStrictPredicate.dropSameSign();
   bool ProvedNonStrictComparison = false;
   bool ProvedNonEquality = false;
 
@@ -11792,9 +11792,8 @@ bool ScalarEvolution::isImpliedCond(CmpPredicate Pred, const SCEV *LHS,
         const SCEV *TruncFoundLHS = getTruncateExpr(FoundLHS, NarrowType);
         const SCEV *TruncFoundRHS = getTruncateExpr(FoundRHS, NarrowType);
         // We cannot preserve samesign after truncation.
-        if (isImpliedCondBalancedTypes(
-                Pred, LHS, RHS, static_cast<ICmpInst::Predicate>(FoundPred),
-                TruncFoundLHS, TruncFoundRHS, CtxI))
+        if (isImpliedCondBalancedTypes(Pred, LHS, RHS, FoundPred.dropSameSign(),
+                                       TruncFoundLHS, TruncFoundRHS, CtxI))
           return true;
       }
     }

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -5641,7 +5641,7 @@ Instruction *InstCombinerImpl::foldICmpWithMinMax(Instruction &I,
   // execute comparisons. For example, `icmp samesign ult umax(X, -46), -32`
   // cannot be decomposed into `(icmp samesign ult X, -46) or (icmp samesign ult
   // -46, -32)`. `X` is allowed to be non-negative here.
-  Pred = static_cast<CmpInst::Predicate>(Pred);
+  Pred = Pred.dropSameSign();
   auto CmpXZ = IsCondKnownTrue(simplifyICmpInst(Pred, X, Z, Q));
   auto CmpYZ = IsCondKnownTrue(simplifyICmpInst(Pred, Y, Z, Q));
   if (!CmpXZ.has_value() && !CmpYZ.has_value())