Enable pure-const discovery in modref.

We newly can handle some extra cases, for example:

struct a {int a,b,c;};
__attribute__ ((noinline))
int init (struct a *a)
{
  a->a=1;
  a->b=2;
  a->c=3;
}
int const_fn ()
{
  struct a a;
  init (&a);
  return a.a + a.b + a.c;
}

Here pure/const stops on the fact that const_fn calls non-const init, while
modref knows that the memory it initializes is local to const_fn.

I ended up reordering passes so early modref is done after early pure-const
mostly to avoid need to change testsuite which greps for const functions
being detects in pure-const.  Stil some testuiste compensation is needed.

gcc/ChangeLog:

2021-11-11  Jan Hubicka  <hubicka@ucw.cz>

	* ipa-modref.c (analyze_function): Do pure/const discovery, return
	true on success.
	(pass_modref::execute): If pure/const is discovered fixup cfg.
	(ignore_edge): Do not ignore pure/const edges.
	(modref_propagate_in_scc): Do pure/const discovery, return true if
	cdtor was promoted pure/const.
	(pass_ipa_modref::execute): If needed remove unreachable functions.
	* ipa-pure-const.c (warn_function_noreturn): Fix whitespace.
	(warn_function_cold): Likewise.
	(skip_function_for_local_pure_const): Move earlier.
	(ipa_make_function_const): Break out from ...
	(ipa_make_function_pure): Break out from ...
	(propagate_pure_const): ... here.
	(pass_local_pure_const::execute): Use it.
	* ipa-utils.h (ipa_make_function_const): Declare.
	(ipa_make_function_pure): Declare.
	* passes.def: Move early modref after pure-const.

gcc/testsuite/ChangeLog:

2021-11-11  Jan Hubicka  <hubicka@ucw.cz>

	* c-c++-common/tm/inline-asm.c: Disable pure-const.
	* g++.dg/ipa/modref-1.C: Update template.
	* gcc.dg/tree-ssa/modref-11.c: Disable pure-const.
	* gcc.dg/tree-ssa/modref-14.c: New test.
	* gcc.dg/tree-ssa/modref-8.c: Do not optimize sibling calls.
	* gfortran.dg/do_subscript_3.f90: Add -O0.

1 files changed, 2 insertions, 0 deletions

diff --git a/gcc/ipa-utils.h b/gcc/ipa-utils.h
index 824780f..e2440a1 100644
--- a/gcc/ipa-utils.h
+++ b/gcc/ipa-utils.h
@@ -50,6 +50,8 @@ bool recursive_call_p (tree, tree);
 /* In ipa-pure-const.c  */
 bool finite_function_p ();
 bool builtin_safe_for_const_function_p (bool *, tree);
+bool ipa_make_function_const (cgraph_node *, bool, bool);
+bool ipa_make_function_pure (cgraph_node *, bool, bool);
 
 /* In ipa-profile.c  */
 bool ipa_propagate_frequency (struct cgraph_node *node);