[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[pinskia at gcc dot gnu dot org]

------- Comment #6 from pinskia at gcc dot gnu dot org  2005-11-30 16:51 -------
Note fixing this will also fix PR 23666 after my patch for moving "- ~a = a+1"
to negate_expr.
But this needs to depend on the fix for PR 25125 since otherwise we expose a
latent bug in convert.c which shows up in the testsuite.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |25125


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2006-04-12 18:10 -------
Didn't we have the canonicalization to put the constant in operand2 if
possible?  A lot of transformations rely on that.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[pinskia at gcc dot gnu dot org]

------- Comment #8 from pinskia at gcc dot gnu dot org  2006-04-13 01:01 -------
(In reply to comment #7)
> Didn't we have the canonicalization to put the constant in operand2 if
> possible?  A lot of transformations rely on that.

Why should they in this case, they only rely on that for operations that are
comunitive and minus is not.  "(-5) - a" is simplier than -a - 5 in reality.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2006-10-22 14:45 -------
Mine.


-- 

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|2006-02-18 17:40:06         |2006-10-22 14:45:16
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2006-10-23 07:19 -------
Subject: Bug 23295

Author: rguenth
Date: Mon Oct 23 07:19:34 2006
New Revision: 117969

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=117969
Log:
2006-10-24  Richard Guenther  <rguenther@suse.de>

        PR middle-end/27132
        PR middle-end/23295
        * builtins.c (fold_binary): Remove checks for flag_wrapv
        and flag_trapv where negate_expr_p covers these cases.

        * gcc.dg/pr27132.c: New testcase.
        * gcc.dg/pr23295.c: Likewise.
        * gcc.dg/tree-ssa/pr23294.c: Adjust patterns.
        * g++.dg/tree-ssa/pr19807.C: Likewise.

2006-10-23  Richard Guenther  <rguenther@suse.de>

        PR middle-end/29548
        * fold-const.c (fold_plusminus_mult_expr): Check exact power
        of two on the absolute value.
        (fold_binary): Fold x * -C to -x * C if x is easily negatable
        and negating -C does not overflow.

Added:
    trunk/gcc/testsuite/gcc.dg/pr23295.c
    trunk/gcc/testsuite/gcc.dg/pr27132.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/fold-const.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/g++.dg/tree-ssa/pr19807.C
    trunk/gcc/testsuite/gcc.dg/tree-ssa/pr23294.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[rguenth at gcc dot gnu dot org]

------- Comment #11 from rguenth at gcc dot gnu dot org  2006-10-23 07:20 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-09 04:44 -------
I am going to move this to minor as this could be considered a regression in a way.
It was introduced by:
        (fold): Optimize "-A - B" as "-B - A" if overflow wraps around.
But in a way since wrapv is false, that means overflow is undefined and can be either wraps or anything 
else.

Maybe Roger can comment on this?

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sayle at gcc dot gnu dot org
           Severity|enhancement                 |minor


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[phython at gcc dot gnu dot org]

------- Additional Comments From phython at gcc dot gnu dot org  2005-08-09 04:26 -------
 This transformation is done with -fwrapv.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-08-09 04:26:46
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-09 03:31 -------
Oh, and we remove one gimplfier tempary variable too.

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-09 03:31 -------
And then we can get optimial rtl generation right away for PPC:
(insn 20 17 26 0 (set (reg/i:SI 3 r3 [ <result> ])
        (minus:SI (const_int -5 [0xfffffffffffffffb])
            (reg:SI 3 r3 [ a ]))) 78 {*rs6000.md:1236} (nil)
    (nil))

If we expand it correctly instead of depending on combine :).

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295

[Bug middle-end/23295] fold does not simplify -a - (5) to (-5) - a

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-09 03:12 -------
This is done in simplify-rtx.c for the rtl level.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |19986
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23295