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.
* 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.