[ConstantRange] Perform increment on APInt (NFC)

This handles the edge case where BitWidth is 1 and doing the
increment gets a value that's not valid in that width, while we
just want wrap-around.

Split out of llvm/llvm-project#80309.

Author: nikic

llvm/lib/Analysis/ValueTracking.cpp

@@ -9518,7 +9518,7 @@ static ConstantRange getRangeForIntrinsic(const IntrinsicInst &II) {
   case Intrinsic::cttz:
     // Maximum of set/clear bits is the bit width.
     return ConstantRange::getNonEmpty(APInt::getZero(Width),
-                                      APInt(Width, Width + 1));
+                                      APInt(Width, Width) + 1);
   case Intrinsic::uadd_sat:
     // uadd.sat(x, C) produces [C, UINT_MAX].
     if (match(II.getOperand(0), m_APInt(C)) ||

llvm/lib/IR/ConstantRange.cpp

@@ -1836,7 +1836,7 @@ ConstantRange ConstantRange::ctlz(bool ZeroIsPoison) const {
   // Zero is either safe or not in the range. The output range is composed by
   // the result of countLeadingZero of the two extremes.
   return getNonEmpty(APInt(getBitWidth(), getUnsignedMax().countl_zero()),
-                     APInt(getBitWidth(), getUnsignedMin().countl_zero() + 1));
+                     APInt(getBitWidth(), getUnsignedMin().countl_zero()) + 1);
 }
 
 static ConstantRange getUnsignedCountTrailingZerosRange(const APInt &Lower,
@@ -1895,7 +1895,7 @@ ConstantRange ConstantRange::cttz(bool ZeroIsPoison) const {
   }
 
   if (isFullSet())
-    return getNonEmpty(Zero, APInt(BitWidth, BitWidth + 1));
+    return getNonEmpty(Zero, APInt(BitWidth, BitWidth) + 1);
   if (!isWrappedSet())
     return getUnsignedCountTrailingZerosRange(Lower, Upper);
   // The range is wrapped. We decompose it into two ranges, [0, Upper) and
@@ -1940,7 +1940,7 @@ ConstantRange ConstantRange::ctpop() const {
   unsigned BitWidth = getBitWidth();
   APInt Zero = APInt::getZero(BitWidth);
   if (isFullSet())
-    return getNonEmpty(Zero, APInt(BitWidth, BitWidth + 1));
+    return getNonEmpty(Zero, APInt(BitWidth, BitWidth) + 1);
   if (!isWrappedSet())
     return getUnsignedPopCountRange(Lower, Upper);
   // The range is wrapped. We decompose it into two ranges, [0, Upper) and