Re: [PATCH] Trust TREE_ADDRESSABLE

[Jan Hubicka <hubicka at ucw dot cz>]

> > On Fri, 13 Jun 2014, Jan Hubicka wrote:
> > 
> > > > 
> > > > When you extract the address and use it.  For example when you
> > > > do auto-parallelization and outline a part of your function it
> > > > passes arrays as addresses.
> > > > 
> > > > Or if you start to introduce address induction variables like
> > > > the vectorizer or IVOPTs does.
> > > 
> > > I see, nothing really done by current early/IPA optimizers and in those cases
> > > we also want to set TREE_ADDRESSABLE bit, too I suppose.
> > > Do you think I should make patch for setting the NOVOPS bits in ipa code?
> > 
> > No, please don't introduce new users of NOVOPS (it's a quite broken
> > hack - it's sth like a 'const' function with side-effects so we should
> > have instead used 'const' and some kind of volatile flag).  We're
> > not using NOVOPS much and that's good (I think handling of such
> > function calls are somewhat broken).
> 
> I meant DECL_NONALIASED.  I will test the patch and lets see.

Hi,
this patch adds the discussed code to set DECL_NOALIASED so we get better AA
with partitioning.  We probably also can sed DECL_NOALIASED for variables
whose address is passed only to external calls that do not capture the
parameters (i.e. memset).

I suppose I can teach ipa-ref code about this, but will need a bit of
extra infrastructure for that, since currently REF_ADDR does not associate
any information about these.

Martin, this is related to your controlled uses.  What do you think about adding
stable UIDs into ipa_ref datastructure and then adding a vector into cgraph edges
that describe what REFs are directly used as parameters of a given callsite?
It will take some work to maintain these, but we will be able to remove them when
call site or parameter was eliminated in a more general way.

I suppose we could also use these to associate REFs with given use in the
satement or constructor (i.e. have pointer to statement as well as pointer to
specific use within the statement). With this we will be able to redirect
references same way as we redirect callgraph edges now.  This is something I
need to for the ipa-visibility optimizations.

Honza

Bootstrapped/regtested and lto-bootstrapped x86_64-linux, will commit it shortly.

	* ipa.c (clear_addressable_bit): Set also DECL_NONALIASED.
	(ipa_discover_readonly_nonaddressable_var): Compute also NONALIASED.
Index: ipa.c
===================================================================
--- ipa.c	(revision 211881)
+++ ipa.c	(working copy)
@@ -669,6 +669,10 @@ clear_addressable_bit (varpool_node *vno
 {
   vnode->address_taken = false;
   TREE_ADDRESSABLE (vnode->decl) = 0;
+  /* Set also non-aliased bit.  In LTO, when program is partitioned, we no longer
+     trust TREE_ADDRESSABLE for TREE_PUBLIC variables and then DECL_NONALIASED is
+     useful to improve code.  */
+  DECL_NONALIASED (vnode->decl) = 1;
   return false;
 }
 
@@ -690,6 +694,7 @@ ipa_discover_readonly_nonaddressable_var
   FOR_EACH_VARIABLE (vnode)
     if (!vnode->alias
 	&& (TREE_ADDRESSABLE (vnode->decl)
+	    || !DECL_NONALIASED (vnode->decl)
 	    || !vnode->writeonly
 	    || !TREE_READONLY (vnode->decl)))
       {
@@ -703,8 +708,8 @@ ipa_discover_readonly_nonaddressable_var
 	  continue;
 	if (!address_taken)
 	  {
-	    if (TREE_ADDRESSABLE (vnode->decl) && dump_file)
-	      fprintf (dump_file, " %s (non-addressable)", vnode->name ());
+	    if ((TREE_ADDRESSABLE (vnode->decl) || !DECL_NONALIASED (vnode->decl)) && dump_file)
+	      fprintf (dump_file, " %s (non-addressable non-aliased)", vnode->name ());
 	    varpool_for_node_and_aliases (vnode, clear_addressable_bit, NULL, true);
 	  }
 	if (!address_taken && !written