[committed] jit: document function pointers

[committed] jit: document function pointers

[David Malcolm]

This patch adds a new function-pointers.rst topic page to the libgccjit
docs.

Committed to trunk as r253257.

gcc/jit/ChangeLog:
	* docs/topics/expressions.rst (Function calls): Add link to
	gcc_jit_context_new_function_ptr_type.
	(Function pointers): Convert to cross-references to
	function-pointers.rst, moving material there.
	* docs/topics/function-pointers.rst: New page.
	* docs/topics/index.rst: Add function-pointers.rst.
	* docs/topics/types.rst (Function pointer types): New section.
	* docs/_build/texinfo/libgccjit.texi: Regenerate.
---
 gcc/jit/docs/topics/expressions.rst       | 21 ++++----
 gcc/jit/docs/topics/function-pointers.rst | 80 +++++++++++++++++++++++++++++++
 gcc/jit/docs/topics/index.rst             |  1 +
 gcc/jit/docs/topics/types.rst             |  6 +++
 4 files changed, 96 insertions(+), 12 deletions(-)
 create mode 100644 gcc/jit/docs/topics/function-pointers.rst

diff --git a/gcc/jit/docs/topics/expressions.rst b/gcc/jit/docs/topics/expressions.rst
index f5c2d0f..76aa4eb 100644
--- a/gcc/jit/docs/topics/expressions.rst
+++ b/gcc/jit/docs/topics/expressions.rst
@@ -416,7 +416,8 @@ Function calls
                                                     int numargs, \
                                                     gcc_jit_rvalue **args)
 
-   Given an rvalue of function pointer type, and the given table of
+   Given an rvalue of function pointer type (e.g. from
+   :c:func:`gcc_jit_context_new_function_ptr_type`), and the given table of
    argument rvalues, construct a call to the function pointer, with the
    result as an rvalue.
 
@@ -452,19 +453,15 @@ Function calls
 Function pointers
 *****************
 
-.. function:: gcc_jit_rvalue *\
-	      gcc_jit_function_get_address (gcc_jit_function *fn,\
-                                            gcc_jit_location *loc)
-
-   Get the address of a function as an rvalue, of function pointer
-   type.
+Function pointers can be obtained:
 
-   This entrypoint was added in :ref:`LIBGCCJIT_ABI_9`; you can test
-   for its presence using
-
-   .. code-block:: c
+  * from a :c:type:`gcc_jit_function` using
+    :c:func:`gcc_jit_function_get_address`, or
 
-      #ifdef LIBGCCJIT_HAVE_gcc_jit_function_get_address
+  * from an existing function using
+    :c:func:`gcc_jit_context_new_rvalue_from_ptr`,
+    using a function pointer type obtained using
+    :c:func:`gcc_jit_context_new_function_ptr_type`.
 
 Type-coercion
 *************
diff --git a/gcc/jit/docs/topics/function-pointers.rst b/gcc/jit/docs/topics/function-pointers.rst
new file mode 100644
index 0000000..b5b9d1b
--- /dev/null
+++ b/gcc/jit/docs/topics/function-pointers.rst
@@ -0,0 +1,80 @@
+.. Copyright (C) 2017 Free Software Foundation, Inc.
+   Originally contributed by David Malcolm <dmalcolm@redhat.com>
+
+   This is free software: you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see
+   <http://www.gnu.org/licenses/>.
+
+.. default-domain:: c
+
+Function pointers
+=================
+
+You can generate calls that use a function pointer via
+:c:func:`gcc_jit_context_new_call_through_ptr`.
+
+To do requires a :c:type:`gcc_jit_rvalue` of the correct function pointer type.
+
+Function pointers for a :c:type:`gcc_jit_function` can be obtained
+via :c:func:`gcc_jit_function_get_address`.
+
+.. function:: gcc_jit_rvalue *\
+	      gcc_jit_function_get_address (gcc_jit_function *fn,\
+                                            gcc_jit_location *loc)
+
+   Get the address of a function as an rvalue, of function pointer
+   type.
+
+   This entrypoint was added in :ref:`LIBGCCJIT_ABI_9`; you can test
+   for its presence using
+
+   .. code-block:: c
+
+      #ifdef LIBGCCJIT_HAVE_gcc_jit_function_get_address
+
+Alternatively, given an existing function, you can obtain a pointer
+to it in :c:type:`gcc_jit_rvalue` form using
+:c:func:`gcc_jit_context_new_rvalue_from_ptr`, using a function pointer
+type obtained using :c:func:`gcc_jit_context_new_function_ptr_type`.
+
+Here's an example of creating a function pointer type corresponding to C's
+:c:type:`void (*) (int, int, int)`:
+
+.. code-block:: c
+
+  gcc_jit_type *void_type =
+    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_VOID);
+  gcc_jit_type *int_type =
+    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_INT);
+
+  /* Build the function ptr type.  */
+  gcc_jit_type *param_types[3];
+  param_types[0] = int_type;
+  param_types[1] = int_type;
+  param_types[2] = int_type;
+
+  gcc_jit_type *fn_ptr_type =
+    gcc_jit_context_new_function_ptr_type (ctxt, NULL,
+					   void_type,
+					   3, param_types, 0);
+
+.. function:: gcc_jit_type *\
+	      gcc_jit_context_new_function_ptr_type (gcc_jit_context *ctxt,\
+				       gcc_jit_location *loc,\
+				       gcc_jit_type *return_type,\
+				       int num_params,\
+				       gcc_jit_type **param_types,\
+				       int is_variadic)
+
+   Generate a :c:type:`gcc_jit_type` for a function pointer with the
+   given return type and parameters.
diff --git a/gcc/jit/docs/topics/index.rst b/gcc/jit/docs/topics/index.rst
index 890f21c..a912a6d 100644
--- a/gcc/jit/docs/topics/index.rst
+++ b/gcc/jit/docs/topics/index.rst
@@ -26,6 +26,7 @@ Topic Reference
    types.rst
    expressions.rst
    functions.rst
+   function-pointers.rst
    locations.rst
    compilation.rst
    compatibility.rst
diff --git a/gcc/jit/docs/topics/types.rst b/gcc/jit/docs/topics/types.rst
index c279222..35a8231 100644
--- a/gcc/jit/docs/topics/types.rst
+++ b/gcc/jit/docs/topics/types.rst
@@ -309,3 +309,9 @@ You can model C `struct` types by creating :c:type:`gcc_jit_struct *` and
        :start-after: /* Quote from here in docs/topics/types.rst.  */
        :end-before: /* Quote up to here in docs/topics/types.rst.  */
        :language: c
+
+Function pointer types
+----------------------
+
+Function pointer types can be created using
+:c:func:`gcc_jit_context_new_function_ptr_type`.
-- 
1.8.5.3