[Bug rtl-optimization/30967] Extra sign/zero extend with word comparison result

[Bug rtl-optimization/30967] Extra sign/zero extend with word comparison result

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30967

[Bug rtl-optimization/30967] New: Extra sign/zero extend with word comparison result

[pinskia at gcc dot gnu dot org]

Testcase:
int f1(int a, int b)
{
  return a == b;
}

------
We produce right now:
_f1:
        xor r4,r3,r4
        cntlzw r4,r4  <--- sign never 1
        srwi r4,r4,5  <--- upper bits defined as 0
        extsw r3,r4
        blr

The sign extend is incorrect as r4's sign will never be 1 and all the upper
bits will always be zero because of srwi.
we have the same issue if the return value is unsigned int also in that there
is an extra zero extend.

This is even with -fsee.


-- 
           Summary: Extra sign/zero extend with word comparison result
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
GCC target triplet: powerpc64-apple-darwin


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30967

[Bug rtl-optimization/30967] Extra sign/zero extend with word comparison result

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-02-26 23:20 -------
I think this is a case where combine (and other passes) don't know that eq is
always signed extended (when the true is not -1):
(insn 9 8 10 2 (set (reg:SI 123)
        (eq:SI (reg:SI 3 3 [ a ])
            (reg:SI 4 4 [ b ]))) 471 {*eqsi} (nil)
    (expr_list:REG_DEAD (reg:DI 3 3 [ a ])
        (expr_list:REG_DEAD (reg:DI 4 4 [ b ])
            (nil))))

(note 10 9 16 2 NOTE_INSN_DELETED)

(insn 16 10 22 2 (set (reg/i:DI 3 3 [ <result> ])
        (sign_extend:DI (reg:SI 123))) 27 {*rs6000.md:393}
(insn_list:REG_DEP_TRUE 9 (nil))
    (expr_list:REG_DEAD (reg:SI 123)
        (nil)))


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30967

[Bug rtl-optimization/30967] Extra sign/zero extend with word comparison result

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2010-03-02 19:14 -------
Still happens on the trunk as of today.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30967

[Bug rtl-optimization/30967] Extra sign/zero extend with word comparison result

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30967

--- Comment #6 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Author: segher
Date: Sat May 16 17:56:55 2015
New Revision: 223250

URL: https://gcc.gnu.org/viewcvs?rev=223250&root=gcc&view=rev
Log:
        Backport from mainline
        2015-05-13  Segher Boessenkool  <segher@kernel.crashing.org>

        PR rtl-optimization/30967
        * config/rs6000/rs6000.c (rs6000_rtx_costs): Don't consider
        destination mode for the cost of scc patterns.

Modified:
    branches/gcc-5-branch/gcc/ChangeLog
    branches/gcc-5-branch/gcc/config/rs6000/rs6000.c

[Bug rtl-optimization/30967] Extra sign/zero extend with word comparison result

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30967

Segher Boessenkool <segher at gcc dot gnu.org> changed:

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

--- Comment #5 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Fixed on trunk.  No backport planned.

[Bug rtl-optimization/30967] Extra sign/zero extend with word comparison result

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30967

--- Comment #4 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Author: segher
Date: Wed May 13 19:14:07 2015
New Revision: 223174

URL: https://gcc.gnu.org/viewcvs?rev=223174&root=gcc&view=rev
Log:
        PR rtl-optimization/30967
        * config/rs6000/rs6000.c (rs6000_rtx_costs): Don't consider
        destination mode for the cost of scc patterns.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/rs6000/rs6000.c

[Bug rtl-optimization/30967] Extra sign/zero extend with word comparison result

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30967

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-05-13
                 CC|                            |segher at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |segher at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #3 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Still happening.  The problem now is that eq:SI is costed as one insn
(which it is not), but eq:DI as three.