extend.texi: (attribute leaf): Document.

	* doc/extend.texi: (attribute leaf): Document.
	* tree.c (local_define_builtin): Handle ECF_LEAF.
	(build_common_builtin_nodes): Set ECF_LEAF where needed.
	* tree.h (ECF_LEAF): New.
	* ipa-reference.c (propagate_bits): For leaf calls propagate ever overwrittable
	and unavailable functions.
	(ipa_init): Put all_module_statics into optimization_summary_obstack.
	(copy_global_bitmap): Do not copy all_module_statics.
	(read_write_all_from_decl): Use cgraph_node argument; handle ECF_LEAF.
	(propagate): Handle overwritable and unavailable leaf functions;
	initialize global info for overwritable and unavailable leaf functions;
	do not free all module statics.
	(ipa_reference_get_not_read_global, ipa_reference_get_not_written_global):
	leaf calls don't clobber local statics.
	* calls.c (flags_from_decl_or_type): Handle leaf.
	* tree-cfg.c (stmt_can_make_abnormal_goto): Leaf functions can't do
	abnormal gotos.

	* c-common.c (handle_leaf_attribute): New function.
	(struct attribute_spec c_common_att): Add leaf.

	* gcc.dg/tree-ssa/leaf.c: New testcase.

From-SVN: r164606

1 files changed, 25 insertions, 0 deletions

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index d737617a..7073c90 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -2671,6 +2671,31 @@ SRAM. The function will be put into a specific section named
 @code{.l1.text}. With @option{-mfdpic}, callers of such functions will use
 an inlined PLT.
 
+@item leaf
+@cindex @code{leaf} function attribute
+Calls to external functions with this attribute must return to the current
+compilation unit only by return or by exception handling. In particular, leaf
+functions are not allowed to call callback function passed to it from current
+compilation unit or directly call functions exported by the unit or longjmp
+into the unit.  Still leaf function might call functions from other complation
+units and thus they are not neccesarily leaf in the sense that they contains no
+function calls at all.
+
+The attribute is intended for library functions to improve dataflow analysis.
+Compiler takes the hint that any data not escaping current compilation unit can
+not be used or modified by the leaf function.  For example, function @code{sin}
+is leaf, function @code{qsort} is not.
+
+Note that the leaf functions might invoke signals and signal handlers might be
+defined in the current compilation unit and use static variables. Only
+compliant way to write such a signal handler is to declare such variables
+@code{volatile}.
+
+The attribute has no effect on functions defined within current compilation
+unit.  This is to allow easy merging of multiple compilation units into one,
+for example, by using the link time optimization.  For this reason the
+attribute is not allowed on types to annotate indirect calls.
+
 @item long_call/short_call
 @cindex indirect calls on ARM
 This attribute specifies how a particular function is called on