Rework the routines that convert AP[S]Int into a string. Now, instead of

returning an std::string by value, it fills in a SmallString/SmallVector
passed in.  This significantly reduces string thrashing in some cases.

More specifically, this:
 - Adds an operator<< and a print method for APInt that allows you to 
   directly send them to an ostream.
 - Reimplements APInt::toString to be much simpler and more efficient
   algorithmically in addition to not thrashing strings quite as much.

This speeds up llvm-dis on kc++ by 7%, and may also slightly speed up the
asmprinter.  This also fixes a bug I introduced into the asmwriter in a
previous patch w.r.t. alias printing.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@54873 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/CppBackend/CPPBackend.cpp

@@ -733,8 +733,8 @@ namespace {
     }
     if (const ConstantInt *CI = dyn_cast<ConstantInt>(CV)) {
       Out << "ConstantInt* " << constName << " = ConstantInt::get(APInt("
-          << cast<IntegerType>(CI->getType())->getBitWidth() << ", "
-          << " \"" << CI->getValue().toStringSigned(10)  << "\", 10));";
+          << cast<IntegerType>(CI->getType())->getBitWidth() << ",  \""
+          << CI->getValue() << "\", 10));";
     } else if (isa<ConstantAggregateZero>(CV)) {
       Out << "ConstantAggregateZero* " << constName
           << " = ConstantAggregateZero::get(" << typeName << ");";