[Bug tree-optimization/67975] Failure to optimise equality between two call sequences

[Bug tree-optimization/67975] Failure to optimise equality between two call sequences

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67975

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-10-15
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  The issue is that to do the optimization we rely on jump-threading
to duplicate out the tails.  We can't see the equivalence of the functions
without
that trick.  Basically the following kind of pattern

  <bb 3>:
  if (x_6(D) < 2.0e+1)
    goto <bb 10>;
  else
    goto <bb 4>;

  <bb 10>:
  goto <bb 5>;

  <bb 4>:

  <bb 5>:
  # iftmp.1_2 = PHI <x_6(D)(10), y_5(D)(4)>
  iftmp.0_7 = __builtin_tan (iftmp.1_2);
  z1_15 = __builtin_cos (iftmp.0_7);
  if (x_6(D) < 2.0e+1)
    goto <bb 11>;
  else
    goto <bb 6>;

  <bb 11>:
  goto <bb 7>;

  <bb 6>:

  <bb 7>:
  # iftmp.3_4 = PHI <x_6(D)(11), y_5(D)(6)>
  iftmp.2_9 = __builtin_tan (iftmp.3_4);
  _23 = __builtin_cos (iftmp.2_9);

requires jump-threading to remove the duplicate check and prove the
PHIs equal.  VRP misses a secondary jump-threading opportunity here
for example.

I will think about this a bit to see whether it's (easily) possible to
value-number the PHIs the same without performing the jump-threading.

[Bug tree-optimization/67975] Failure to optimise equality between two call sequences

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67975

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
int foo (int x, int y)
{
  int a = x > 5 ? x : y;
  int b = x > 5 ? x : y;
  return a == b;
}

this should be handled in FRE1 already (well, if hopefully easily possible).
Currently two PHIs are only ever considered to have the same value if they
appear in the same basic-block.

[Bug tree-optimization/67975] Failure to optimise equality between two call sequences

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67975

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
I have a prototype that handles (extended) diamonds.  With this FRE1 is able to
optimize the check to 1 (with -O -ffast-math).

[Bug tree-optimization/67975] Failure to optimise equality between two call sequences

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67975

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
https://gcc.gnu.org/ml/gcc-patches/2015-10/msg01580.html

Hope that fixes all cases you ran into.

[Bug tree-optimization/67975] Failure to optimise equality between two call sequences

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67975

--- Comment #5 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #4)
> https://gcc.gnu.org/ml/gcc-patches/2015-10/msg01580.html
> 
> Hope that fixes all cases you ran into.

Yeah, thanks.  That fixes the builtins-20.c failures that I was seeing
after moving fold_strip_sign_ops to gimple.

[Bug tree-optimization/67975] Failure to optimise equality between two call sequences

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67975

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

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

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.

[Bug tree-optimization/67975] Failure to optimise equality between two call sequences

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67975

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Mon Oct 19 14:00:28 2015
New Revision: 228971

URL: https://gcc.gnu.org/viewcvs?rev=228971&root=gcc&view=rev
Log:
2015-10-19  Richard Biener  <rguenther@suse.de>

        PR tree-optimization/67975
        * tree-cfg.h (extract_true_false_controlled_edges): Declare.
        * tree-cfg.c (extract_true_false_controlled_edges): Split out
        core worker from ...
        * tree-ssa-loop-im.c (extract_true_false_args_from_phi): ... here.
        * tree-ssa-sccvn.c (vn_phi_compute_hash): Hash number of args
        instead of block number for PHIs with two or one args.
        (vn_phi_eq): Compare edge predicates of PHIs that are in different
        blocks.

        * gcc.dg/tree-ssa/ssa-fre-50.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-50.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-cfg.c
    trunk/gcc/tree-cfg.h
    trunk/gcc/tree-ssa-loop-im.c
    trunk/gcc/tree-ssa-sccvn.c