This patch implements generic type query and conversion functions,

This patch implements generic type query and conversion functions,
and applies them to the use of cgraph_node, varpool_node, and symtab_node.

The functions are:

bool is_a <TYPE> (pointer)
  Tests whether the pointer actually points to a more derived TYPE.

TYPE *as_a <TYPE> (pointer)
  Converts pointer to a TYPE*.

TYPE *dyn_cast <TYPE> (pointer)
  Converts pointer to TYPE* if and only if "is_a <TYPE> pointer".
  Otherwise, returns NULL.
  This function is essentially a checked down cast.

These functions reduce compile time and increase type safety when treating a
generic item as a more specific item.  In essence, the code change is from

  if (symtab_function_p (node))
    {
      struct cgraph_node *cnode = cgraph (node);
      ....
    }

to

  if (cgraph_node *cnode = dyn_cast <cgraph_node> (node))
    {
      ....
    }

The necessary conditional test defines a variable that holds a known good
pointer to the specific item and avoids subsequent conversion calls and
the assertion checks that may come with them.

When, the property test is embedded within a larger condition, the variable
declaration gets pulled out of the condition.  (This leaves some room for
using the variable inappropriately.)

  if (symtab_variable_p (node)
      && varpool (node)->finalized)
    varpool_analyze_node (varpool (node));

becomes

  varpool_node *vnode = dyn_cast <varpool_node> (node);
  if (vnode && vnode->finalized)
    varpool_analyze_node (vnode);

Note that we have converted two sets of assertions in the calls to varpool
into safe and efficient use of a variable.

There are remaining calls to symtab_function_p and symtab_variable_p that
do not involve a pointer to a more specific type.  These have been converted
to calls to a functions is_a <cgraph_node> and is_a <varpool_node>.  The
original predicate functions have been removed.

The cgraph.h header defined both a struct and a function with the name
varpool_node.  This name overloading can cause some unintuitive error messages
when, as is common in C++, one omits the struct keyword when using the type.
I have renamed the function to varpool_node_for_decl.

Tested on x86_64.

Index: gcc/ChangeLog

2012-10-31  Lawrence Crowl  <crowl@google.com>

	* is-a.h: New.
	(is_a <T> (U*)): New.  Test for is-a relationship.
	(as_a <T> (U*)): New.  Treat as a derived type.
	(dyn_cast <T> (U*)): New.  Conditionally cast based on is_a.
	* cgraph.h (varpool_node): Rename to varpool_node_for_decl.
	Adjust callers to match.
	(is_a_helper <cgraph_node>::test (symtab_node_def *)): New.
	(is_a_helper <varpool_node>::test (symtab_node_def *)): New.
	(symtab_node_def::try_function): New.  Change most calls to
	symtab_function_p with calls to dyn_cast <cgraph_node> (p).
	(symtab_node_def::try_variable): New.  Change most calls to
	symtab_variable_p with calls to dyn_cast <varpool_node> (p).
	(symtab_function_p): Remove.  Change callers to use
        is_a <cgraph_node> (p) instead.
	(symtab_variable_p): Remove.  Change callers to use
        is_a <varpool_node> (p) instead.
	* cgraph.c (cgraph_node_for_asm): Remove redundant call to
	symtab_node_for_asm.
	* cgraphunit.c (symbol_finalized_and_needed): New.
	(symbol_finalized): New.
	(cgraph_analyze_functions): Split complicated conditionals out into
	above new functions.
	* Makefile.in (CGRAPH_H): Add is-a.h as used by cgraph.h.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@193051 138bc75d-0d04-0410-961f-82ee72b054a4