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
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 80dda1f..c372874 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -4992,7 +4992,7 @@
   }
 
   if (const ConstantSDNode *CSDN = dyn_cast<ConstantSDNode>(this)) {
-    cerr << "<" << CSDN->getAPIntValue().toStringUnsigned() << ">";
+    cerr << "<" << CSDN->getAPIntValue() << ">";
   } else if (const ConstantFPSDNode *CSDN = dyn_cast<ConstantFPSDNode>(this)) {
     if (&CSDN->getValueAPF().getSemantics()==&APFloat::IEEEsingle)
       cerr << "<" << CSDN->getValueAPF().convertToFloat() << ">";