[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

--- Comment #7 from Marc Glisse <glisse at gcc dot gnu.org> ---
While looking at some unrelated issue, I noticed the following:

  _41 = operator new (28);
...
  if (_41 != &_S_empty_rep_storage)

which happens with a simple use of std::string (with some extra inlining).
__builtin_malloc(42)==&var is not optimized either, so it isn't (only) an issue
with operator new.

If the general case is too dangerous, maybe there is at least some subset that
could safely be optimized?

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

--- Comment #8 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 14 Aug 2014, glisse at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962
> 
> --- Comment #7 from Marc Glisse <glisse at gcc dot gnu.org> ---
> While looking at some unrelated issue, I noticed the following:
> 
>   _41 = operator new (28);
> ...
>   if (_41 != &_S_empty_rep_storage)
> 
> which happens with a simple use of std::string (with some extra inlining).
> __builtin_malloc(42)==&var is not optimized either, so it isn't (only) an issue
> with operator new.
> 
> If the general case is too dangerous, maybe there is at least some subset that
> could safely be optimized?

Well, not sure if really "dangerous", but yes, doing pointer against
address-of-decl disambiguation should be easily possible.

I'll try to hack sth together later today.

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
Created attachment 33336
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33336&action=edit
patch

Like this - does it help the particular case?

Note that one issue is that points-to doesn't track NULL-ness reliably
(like may-point to zero if it may point to a weak decl), and we drop
maybe-NULL-ness because we don't use it.  Likewise we don't keep track
of pointers to CONST_DECLs or LABEL_DECLs or FUNCTION_DECLs (we simply
drop them on the floor rather than treating them as "anything").

The patch doesn't bootstrap which means it probably reveals bugs in
points-to.  This is what I meant with "dangerous" ;)

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

Marc Glisse <glisse at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |glisse at gcc dot gnu.org

--- Comment #10 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #9)
> Created attachment 33336 [details]
> patch
> 
> Like this - does it help the particular case?

_S_empty_rep_storage has DECL_WEAK, so it doesn't help here :-(

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |zhongyunde at huawei dot com

--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> ---
*** Bug 110103 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

--- Comment #16 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:f3e5f4c58591f5dacdd14a65ec47bbe310df02a0

commit r15-580-gf3e5f4c58591f5dacdd14a65ec47bbe310df02a0
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Mar 11 11:17:32 2024 +0100

    tree-optimization/13962 - handle ptr-ptr compares in ptrs_compare_unequal

    Now that we handle pt.null conservatively we can implement the missing
    tracking of constant pool entries (aka STRING_CST) and handle
    ptr-ptr compares using points-to info in ptrs_compare_unequal.

            PR tree-optimization/13962
            PR tree-optimization/96564
            * tree-ssa-alias.h (pt_solution::const_pool): New flag.
            * tree-ssa-alias.cc (ptrs_compare_unequal): Handle pointer-pointer
            compares.
            (dump_points_to_solution): Dump the const_pool flag, fix guard
            of flag dumping.
            * gimple-pretty-print.cc (pp_points_to_solution): Likewise.
            * tree-ssa-structalias.cc (find_what_var_points_to): Set
            the const_pool flag for STRING.
            (pt_solution_ior_into): Handle the const_pool flag.
            (ipa_escaped_pt): Initialize it.

            * gcc.dg/tree-ssa/alias-39.c: New testcase.
            * g++.dg/vect/pr68145.cc: Use -fno-tree-pta to avoid UB
            to manifest in transforms no longer vectorizing this testcase
            for an ICE.

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #17 from Richard Biener <rguenth at gcc dot gnu.org> ---
I'm closing this as fixed now.  The feature is there, improvements can be made
I guess but first get testcases that are not handled (combine with prange info
is one item).

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2009-02-22 20:20 -------
Easy but dangerous ;)


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2006-01-13 04:44:24         |2009-02-22 20:20:56
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[steven at gcc dot gnu dot org]

------- Comment #5 from steven at gcc dot gnu dot org  2009-02-22 19:09 -------
Richi, this may be easy to fix on the AIB...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[dann at ics dot uci dot edu]

------- Comment #4 from dann at ics dot uci dot edu  2006-12-12 06:01 -------
Subject: Re:  [tree-ssa] make "fold" use alias information to optimize pointer
comparisons

"steven at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> writes:

  > ------- Comment #3 from steven at gcc dot gnu dot org  2006-12-10 18:18
-------
  > Is this fixed?

No, it's not.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[steven at gcc dot gnu dot org]

------- Comment #3 from steven at gcc dot gnu dot org  2006-12-10 18:18 -------
Is this fixed?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[dnovillo at gcc dot gnu dot org]

-- 

dnovillo at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dnovillo at gcc dot gnu dot
                   |                            |org
         AssignedTo|dnovillo at gcc dot gnu dot |unassigned at gcc dot gnu
                   |org                         |dot org
             Status|ASSIGNED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

[Bug tree-optimization/13962] [tree-ssa] make "fold" use alias information to optimize pointer comparisons

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.5.0                       |---


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962