Don't allocate unnecessarily in APInt::operator[+-]. NFC.

APInt::operator+(uint64_t) just forwarded to operator+(const APInt&).

Constructing the APInt for the RHS takes an allocation which isn't
required.  Also, for APInt's in the slow path, operator+ would
call add() internally which iterates over both arrays of values.  Instead
we can use add_1 and sub_1 which only iterate while there is something to do.

Using the memory for 'opt -O2 verify-uselistorder.lto.opt.bc -o opt.bc'
(see r236629 for details), this reduces the number of allocations from
23.9M to 22.7M.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270959 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/APInt.cpp

@@ -480,6 +480,15 @@ APInt APInt::operator+(const APInt& RHS) const {
   return Result;
 }
 
+APInt APInt::operator+(uint64_t RHS) const {
+  if (isSingleWord())
+    return APInt(BitWidth, VAL + RHS);
+  APInt Result(*this);
+  add_1(Result.pVal, Result.pVal, getNumWords(), RHS);
+  Result.clearUnusedBits();
+  return Result;
+}
+
 APInt APInt::operator-(const APInt& RHS) const {
   assert(BitWidth == RHS.BitWidth && "Bit widths must be the same");
   if (isSingleWord())
@@ -490,6 +499,15 @@ APInt APInt::operator-(const APInt& RHS) const {
   return Result;
 }
 
+APInt APInt::operator-(uint64_t RHS) const {
+  if (isSingleWord())
+    return APInt(BitWidth, VAL - RHS);
+  APInt Result(*this);
+  sub_1(Result.pVal, getNumWords(), RHS);
+  Result.clearUnusedBits();
+  return Result;
+}
+
 bool APInt::EqualSlowCase(const APInt& RHS) const {
   return std::equal(pVal, pVal + getNumWords(), RHS.pVal);
 }