[Bug target/41076] [avr] pessimal code for logical OR of 8-bit fields

[Bug target/41076] [avr] pessimal code for logical OR of 8-bit fields

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41076

--- Comment #2 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-05-16 14:20:25 UTC ---
Author: gjl
Date: Mon May 16 14:20:19 2011
New Revision: 173792

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=173792
Log:
    PR target/27663
    PR target/41076
    * config/avr/predicates.md (const_8_16_24_operand): New predicate.
    * config/avr/avr.md ("*ior<mode>qi.byte0",
    "*ior<mode>qi.byte1-3"): New define_insn_and_split patterns.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/avr/avr.md
    trunk/gcc/config/avr/predicates.md

[Bug target/41076] [avr] pessimal code for logical OR of 8-bit fields

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41076

Georg-Johann Lay <gjl at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011-09-11
         AssignedTo|unassigned at gcc dot       |gjl at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #3 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-09-11 20:59:28 UTC ---
Created attachment 25242
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25242
Some test cases

[Bug target/41076] [avr] pessimal code for logical OR of 8-bit fields

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41076

Georg-Johann Lay <gjl at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|avr-elf                     |avr
           Priority|P3                          |P4
            Version|unknown                     |4.6.1
   Target Milestone|---                         |4.7.0
           Severity|normal                      |enhancement

[Bug target/41076] [avr] pessimal code for logical OR of 8-bit fields

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41076

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.7.0                       |4.7.1

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-03-22 08:26:23 UTC ---
GCC 4.7.0 is being released, adjusting target milestone.

[Bug target/41076] [avr] pessimal code for logical OR of 8-bit fields

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41076

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

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

--- Comment #5 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-07-02 13:52:40 UTC ---
Fixed I suppose.

[Bug target/41076] [avr] pessimal code for logical OR of 8-bit fields

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41076

Georg-Johann Lay <gjl at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |
   Target Milestone|4.7.1                       |---
           Severity|enhancement                 |normal

--- Comment #6 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2013-01-22 22:31:11 UTC ---
(In reply to comment #5)
> Fixed I suppose.

Unfortunately, not

extern unsigned char read8 (void);

unsigned short read16 (void)
{
    unsigned char lo, hi;

    hi = read8();
    lo = read8();
    return lo | hi << 8;
}


with 4.8.0 -S -Os the compiler needs 5 instructions (29, 37, 30, 38) for an
operation that is basically a no-op:


read16:
    push r28     ;  31    pushqi1/1    [length = 1]
/* prologue: function */
/* frame size = 0 */
/* stack size = 1 */
.L__stack_usage = 1
    call read8     ;  5    call_value_insn/2    [length = 2]
    mov r28,r24     ;  6    movqi_insn/1    [length = 1]
    call read8     ;  7    call_value_insn/2    [length = 2]
    mov r18,r28     ;  28    movqi_insn/1    [length = 1]
    ldi r19,0     ;  29    movqi_insn/1    [length = 1]
    mov r19,r18     ;  37    *ashlhi3_const/3    [length = 2]
    clr r18
    or r18,r24     ;  30    iorqi3/1    [length = 1]
    movw r24,r18     ;  38    *movhi/1    [length = 1]
/* epilogue start */
    pop r28     ;  34    popqi    [length = 1]
    ret     ;  35    return_from_epilogue    [length = 1]

[Bug target/41076] [avr] pessimal code for logical OR of 8-bit fields

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41076

Georg-Johann Lay <gjl at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |matthijs at stdin dot nl

--- Comment #7 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
*** Bug 60145 has been marked as a duplicate of this bug. ***

[Bug target/41076] [avr] pessimal code for logical OR of 8-bit fields

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2009-08-15 09:55 -------
because this is what C says you are doing:

  return (unsigned short) ((int) a | ((int) b << 8));

which is harder to transform back into what you expect.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41076