[IR] CmpInst: Add getFlippedSignednessPredicate()

And refactor a few places to use it

llvm/include/llvm/IR/InstrTypes.h

@@ -942,6 +942,18 @@ public:
     return getUnsignedPredicate(getPredicate());
   }
 
+  /// For example, SLT->ULT, ULT->SLT, SLE->ULE, ULE->SLE, EQ->Failed assert
+  /// @returns the unsigned version of the signed predicate pred or
+  ///          the signed version of the signed predicate pred.
+  static Predicate getFlippedSignednessPredicate(Predicate pred);
+
+  /// For example, SLT->ULT, ULT->SLT, SLE->ULE, ULE->SLE, EQ->Failed assert
+  /// @returns the unsigned version of the signed predicate pred or
+  ///          the signed version of the signed predicate pred.
+  Predicate getFlippedSignednessPredicate() {
+    return getFlippedSignednessPredicate(getPredicate());
+  }
+
   /// This is just a convenience.
   /// Determine if this is true when both operands are the same.
   bool isTrueWhenEqual() const {

llvm/lib/IR/Instructions.cpp

@@ -3898,6 +3898,18 @@ bool CmpInst::isSigned(Predicate predicate) {
   }
 }
 
+CmpInst::Predicate CmpInst::getFlippedSignednessPredicate(Predicate pred) {
+  assert(CmpInst::isRelational(pred) &&
+         "Call only with non-equality predicates!");
+
+  if (isSigned(pred))
+    return getUnsignedPredicate(pred);
+  if (isUnsigned(pred))
+    return getSignedPredicate(pred);
+
+  llvm_unreachable("Unknown predicate!");
+}
+
 bool CmpInst::isOrdered(Predicate predicate) {
   switch (predicate) {
     default: return false;

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -1614,15 +1614,13 @@ Instruction *InstCombinerImpl::foldICmpXorConstant(ICmpInst &Cmp,
   if (Xor->hasOneUse()) {
     // (icmp u/s (xor X SignMask), C) -> (icmp s/u X, (xor C SignMask))
     if (!Cmp.isEquality() && XorC->isSignMask()) {
-      Pred = Cmp.isSigned() ? Cmp.getUnsignedPredicate()
+      Pred = Cmp.getFlippedSignednessPredicate();
-                            : Cmp.getSignedPredicate();
       return new ICmpInst(Pred, X, ConstantInt::get(X->getType(), C ^ *XorC));
     }
 
     // (icmp u/s (xor X ~SignMask), C) -> (icmp s/u X, (xor C ~SignMask))
     if (!Cmp.isEquality() && XorC->isMaxSignedValue()) {
-      Pred = Cmp.isSigned() ? Cmp.getUnsignedPredicate()
+      Pred = Cmp.getFlippedSignednessPredicate();
-                            : Cmp.getSignedPredicate();
       Pred = Cmp.getSwappedPredicate(Pred);
       return new ICmpInst(Pred, X, ConstantInt::get(X->getType(), C ^ *XorC));
     }
@@ -4053,15 +4051,13 @@ Instruction *InstCombinerImpl::foldICmpBinOp(ICmpInst &I,
       if (match(BO0->getOperand(1), m_APInt(C))) {
         // icmp u/s (a ^ signmask), (b ^ signmask) --> icmp s/u a, b
         if (C->isSignMask()) {
-          ICmpInst::Predicate NewPred =
+          ICmpInst::Predicate NewPred = I.getFlippedSignednessPredicate();
-              I.isSigned() ? I.getUnsignedPredicate() : I.getSignedPredicate();
           return new ICmpInst(NewPred, BO0->getOperand(0), BO1->getOperand(0));
         }
 
         // icmp u/s (a ^ maxsignval), (b ^ maxsignval) --> icmp s/u' a, b
         if (BO0->getOpcode() == Instruction::Xor && C->isMaxSignedValue()) {
-          ICmpInst::Predicate NewPred =
+          ICmpInst::Predicate NewPred = I.getFlippedSignednessPredicate();
-              I.isSigned() ? I.getUnsignedPredicate() : I.getSignedPredicate();
           NewPred = I.getSwappedPredicate(NewPred);
           return new ICmpInst(NewPred, BO0->getOperand(0), BO1->getOperand(0));
         }