Add an no_reorder attribute for LTO

Some projects need to prevent reordering of specific top level
declarations with LTO, in particular declarations defining init calls.

The only way to do that with LTO was to use -fno-toplevel-reorder,
which stops reordering for all declarations and makes LTO partitioning
less efficient.

This patch adds a new no_reorder attribute that stops reordering only
for the marked declaration. The program can then only mark e.g. the
initcalls and leave all the other declarations alone.

The patch does:

- Adds the new no_reorder attribute for the C family.
- Initializes a new no_reorder flag in the symtab_nodes in the
function visibility flag.
- Maintains the no_reorder flag when creating new nodes.
- Changes the partition code to always keep a separate
sorted queue of ordered nodes and flush them in order with the other
nodes. This is used by all nodes with -fno-toplevel-reorder,
and only the marked ones without it.
Parts of the old -fno-toplevel-reorder code paths are reused.
- Adds various checks throughout the tree to make no_reorder
marked functions behave the same as with -fno-toplevel-reorder
- Changes the LTO streamer to serialize the no_reorder attribute.

gcc/c-family/:

2014-09-23  Andi Kleen  <ak@linux.intel.com>

	* c-common.c (handle_no_reorder_attribute): New function.
	(c_common_attribute_table): Add no_reorder attribute.

gcc/:

2014-09-23  Andi Kleen  <ak@linux.intel.com>

	* cgraph.h (symtab_node): Add no_reorder attribute.
	(symbol_table::output_asm_statements): Remove.
	* cgraphclones.c (cgraph_node::create_clone): Copy no_reorder.
	(cgraph_node::create_version_clone): Dito.
	(symbol_table::output_asm_statements): Remove.
	* trans-mem.c (ipa_tm_create_version_alias): Dito.
	* cgraphunit.c (varpool_node::finalize_decl): Check no_reorder.
	(output_in_order): Add no_reorder flag. Only handle no_reorder
	nodes when set.
	(symbol_table::compile): Add separate pass for no_reorder nodes.
	(process_common_attributes): Set no_reorder flag in symtab node.
	Add node argument.
	(process_function_and_variable_attributes): Pass symtab nodes to
	process_common_attributes.
	* doc/extend.texi (no_reorder): Document no_reorder attribute.
	* lto-cgraph.c (lto_output_node): Serialize no_reorder.
	(lto_output_varpool_node): Dito.
	(input_overwrite_node): Dito.
	(input_varpool_node): Dito.
	* varpool.c (varpool_node::add): Set no_reorder attribute.
	(symbol_table::remove_unreferenced_decls): Handle no_reorder.
	(symbol_table::output_variables): Dito.
	* symtab.c (symtab_node::dump_base): Print no_reorder.

gcc/lto/:

2014-09-23  Andi Kleen  <ak@linux.intel.com>

	* lto-partition.c (node_cmp): Update comment.
	(varpool_node_cmp): Use symtab_node for comparison.
	(add_sorted_nodes): New function.
	(lto_balanced_map): Change to keep ordered queue
	of ordered node. Handle no_reorder attribute.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@215537 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 11 insertions, 1 deletions

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 4eef9001820..c78ffb2dabc 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -2180,7 +2180,7 @@ attributes are currently defined for functions on all targets:
 @code{returns_nonnull}, @code{gnu_inline},
 @code{externally_visible}, @code{hot}, @code{cold}, @code{artificial},
 @code{no_sanitize_address}, @code{no_address_safety_analysis},
-@code{no_sanitize_undefined},
+@code{no_sanitize_undefined}, @code{no_reorder},
 @code{error} and @code{warning}.
 Several other attributes are defined for functions on particular
 target systems.  Other attributes, including @code{section} are
@@ -3472,6 +3472,16 @@ my_memcpy (void *dest, const void *src, size_t len)
         __attribute__((nonnull));
 @end smallexample
 
+@item no_reorder
+@cindex @code{no_reorder} function or variable attribute
+Do not reorder functions or variables marked @code{no_reorder}
+against each other or top level assembler statements the executable.
+The actual order in the program will depend on the linker command
+line. Static variables marked like this are also not removed.
+This has a similar effect
+as the @option{-fno-toplevel-reorder} option, but only applies to the
+marked symbols.
+
 @item returns_nonnull
 @cindex @code{returns_nonnull} function attribute
 The @code{returns_nonnull} attribute specifies that the function