Reimplement the parameter attributes support, phase #1. hilights:

1. There is now a "PAListPtr" class, which is a smart pointer around
   the underlying uniqued parameter attribute list object, and manages
   its refcount.  It is now impossible to mess up the refcount.
2. PAListPtr is now the main interface to the underlying object, and
   the underlying object is now completely opaque.
3. Implementation details like SmallVector and FoldingSet are now no
   longer part of the interface.
4. You can create a PAListPtr with an arbitrary sequence of
   ParamAttrsWithIndex's, no need to make a SmallVector of a specific 
   size (you can just use an array or scalar or vector if you wish).
5. All the client code that had to check for a null pointer before
   dereferencing the pointer is simplified to just access the 
   PAListPtr directly.
6. The interfaces for adding attrs to a list and removing them is a
   bit simpler.

Phase #2 will rename some stuff (e.g. PAListPtr) and do other less 
invasive changes.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48289 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Bitcode/Reader/BitcodeReader.h

@@ -15,6 +15,7 @@
 #define BITCODE_READER_H
 
 #include "llvm/ModuleProvider.h"
+#include "llvm/ParameterAttributes.h"
 #include "llvm/Type.h"
 #include "llvm/User.h"
 #include "llvm/Bitcode/BitstreamReader.h"
@@ -24,7 +25,6 @@
 
 namespace llvm {
   class MemoryBuffer;
-  class ParamAttrsList;
   
 class BitcodeReaderValueList : public User {
   std::vector<Use> Uses;
@@ -93,7 +93,7 @@ class BitcodeReader : public ModuleProvider {
   /// ParamAttrs - The set of parameter attributes by index.  Index zero in the
   /// file is for null, and is thus not represented here.  As such all indices
   /// are off by one.
-  std::vector<const ParamAttrsList*> ParamAttrs;
+  std::vector<PAListPtr> ParamAttrs;
   
   /// FunctionBBs - While parsing a function body, this is a list of the basic
   /// blocks for the function.
@@ -156,10 +156,10 @@ private:
     if (ID >= FunctionBBs.size()) return 0; // Invalid ID
     return FunctionBBs[ID];
   }
-  const ParamAttrsList *getParamAttrs(unsigned i) const {
+  PAListPtr getParamAttrs(unsigned i) const {
     if (i-1 < ParamAttrs.size())
       return ParamAttrs[i-1];
-    return 0;
+    return PAListPtr();
   }
   
   /// getValueTypePair - Read a value/type pair out of the specified record from