Drop isKnownNonNegative() call

Author: leo-ard

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -5554,20 +5554,16 @@ Instruction *InstCombinerImpl::foldICmpWithZextOrSext(ICmpInst &ICmp) {
         return new ICmpInst(ICmp.getPredicate(), Builder.CreateOr(X, Y),
                             Constant::getNullValue(X->getType()));
 
-      // Treat "zext nneg" as "sext"
+      // If we have mismatched casts and zext has the nneg flag, we can 
+      //  treat the "zext nneg" as "sext". Otherwise, we cannot fold and quit. 
+
       auto *NonNegInst0 = dyn_cast<PossiblyNonNegInst>(ICmp.getOperand(0));
       auto *NonNegInst1 = dyn_cast<PossiblyNonNegInst>(ICmp.getOperand(1));
 
       bool IsNonNeg0 = NonNegInst0 && NonNegInst0->hasNonNeg();
       bool IsNonNeg1 = NonNegInst1 && NonNegInst1->hasNonNeg();
 
-      // If we have mismatched casts, treat the zext of a non-negative source as
-      // a sext to simulate matching casts. Otherwise, we are done.
-      // TODO: Can we handle some predicates (equality) without non-negative?
-      if ((IsZext0 &&
-           (IsNonNeg0 || isKnownNonNegative(X, DL, 0, &AC, &ICmp, &DT))) ||
-          (IsZext1 &&
-           (IsNonNeg1 || isKnownNonNegative(Y, DL, 0, &AC, &ICmp, &DT))))
+      if ((IsZext0 && IsNonNeg0) || (IsZext1 && IsNonNeg1))
         IsSignedExt = true;
       else
         return nullptr;