[Bug target/49687] New: AVR: Missed optimization for widening MUL

[Bug target/49687] New: AVR: Missed optimization for widening MUL

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

           Summary: AVR: Missed optimization for widening MUL
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: gjl@gcc.gnu.org
            Target: avr


With avr-gcc 4.6.1 and 
-Os -mmcu=atmega88 -S -dp

int mul8_55 (char x)
{
    return x * 55;
}

gets compiled to 

mul8_55:
    ldi r25,lo8(55)     ;  7    *movqi/2    [length = 1]
    muls r24,r25     ;  8    mulqihi3    [length = 3]
    movw r24,r0
    clr r1
    ret     ;  26    return    [length = 1]

which is fine.  If the constant is 126, however, the result is bloated and
might be related to PR36467, i.e. MUL* is better than shift.

mul8_126:
    clr r25     ;  7    extendqihi2/1    [length = 3]
    sbrc r24,7
    com r25
    movw r18,r24     ;  28    *movhi/1    [length = 1]
    lsl r18     ;  33    *ashlhi3_const/2    [length = 2]
    rol r19
    lsr r25     ;  34    *ashlhi3_const/5    [length = 5]
    mov r25,r24
    clr r24
    ror r25
    ror r24
    sub r24,r18     ;  12    subhi3/1    [length = 2]
    sbc r25,r19
    ret     ;  31    return    [length = 1]

If the constant is 155, a MUL is invented, but a widening MUL would be smarter:

mul8_155:
    mov r20,r24     ;  6    extendqihi2/2    [length = 4]
    clr r21
    sbrc r20,7
    com r21
    ldi r18,lo8(155)     ;  7    *movhi/4    [length = 2]
    ldi r19,hi8(155)
    mul r20,r18     ;  8    *mulhi3_enh    [length = 7]
    movw r24,r0
    mul r20,r19
    add r25,r0
    mul r21,r18
    add r25,r0
    clr r1
    ret     ;  26    return    [length = 1]

[Bug target/49687] AVR: Missed optimization for widening MUL

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

--- Comment #1 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-09 09:37:40 UTC ---
Created attachment 24724
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24724
C Test case

[Bug target/49687] AVR: Missed optimization for widening MUL

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |eric.weddington at atmel
                   |                            |dot com
   Target Milestone|---                         |4.7.0
      Known to fail|                            |4.6.1

[Bug target/49687] AVR: Missed optimization for widening MUL

[eric.weddington at atmel dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

--- Comment #2 from Eric Weddington <eric.weddington at atmel dot com> 2011-07-14 18:41:56 UTC ---
Created attachment 24758
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24758
Test case results using GCC 4.3.3 (WinAVR 20100110)

[Bug target/49687] [4.6 Regression][avr] Missed optimization for widening MUL

[eric.weddington at atmel dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

Eric Weddington <eric.weddington at atmel dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.07.14 18:45:17
            Summary|AVR: Missed optimization    |[4.6 Regression][avr]
                   |for widening MUL            |Missed optimization for
                   |                            |widening MUL
     Ever Confirmed|0                           |1

--- Comment #3 from Eric Weddington <eric.weddington at atmel dot com> 2011-07-14 18:45:17 UTC ---
The test case results using GCC 4.3.3 (WinAVR 20100110) shows that the mul8_126
case is smaller:

.global    mul8_126
    .type    mul8_126, @function
mul8_126:
/* prologue: function */
/* frame size = 0 */
    mov r18,r24     ;  2    *movqi/1    [length = 1]
    ldi r24,lo8(126)     ;  6    *movqi/2    [length = 1]
    muls r18,r24     ;  7    mulqihi3    [length = 3]
    movw r18,r0
    clr r1
    movw r24,r18     ;  32    *movhi/1    [length = 1]
/* epilogue start */
    ret     ;  30    return    [length = 1]
    .size    mul8_126, .-mul8_126

So this is a regression wrt to gcc 4.6.1.

The case of mul8_155 shows the identical problem as for gcc 4.6.1.

[Bug target/49687] [4.6 Regression][avr] Missed optimization for widening MUL

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

--- Comment #4 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-20 17:23:31 UTC ---
Author: gjl
Date: Wed Jul 20 17:23:28 2011
New Revision: 176527

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=176527
Log:

    PR target/36467
    PR target/49687
    * config/avr/avr.md (mulhi3): Use register_or_s9_operand for
    operand2 and expand appropriately if there is a CONST_INT in
    operand2.
    (usmulqihi3): New insn.
    (*sumulqihi3): New insn.
    (*osmulqihi3): New insn.
    (*oumulqihi3): New insn.
    (*muluqihi3.uconst): New insn_and_split.
    (*muluqihi3.sconst): New insn_and_split.
    (*mulsqihi3.sconst): New insn_and_split.
    (*mulsqihi3.uconst): New insn_and_split.
    (*mulsqihi3.oconst): New insn_and_split.
    (*ashifthi3.signx.const): New insn_and_split.
    (*ashifthi3.signx.const7): New insn_and_split.
    (*ashifthi3.zerox.const): New insn_and_split.
    (mulsqihi3): New insn.
    (muluqihi3): New insn.
    (muloqihi3): New insn.
    * config/avr/predicates.md (const_2_to_7_operand): New.
    (const_2_to_6_operand): New.
    (u8_operand): New.
    (s8_operand): New.
    (o8_operand): New.
    (s9_operand): New.
    (register_or_s9_operand): New.


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

[Bug target/49687] [4.6 Regression][avr] Missed optimization for widening MUL

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

--- Comment #5 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-28 08:03:12 UTC ---
Author: gjl
Date: Thu Jul 28 08:03:07 2011
New Revision: 176862

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=176862
Log:

    PR target/49687
    * config/avr/t-avr (LIB1ASMFUNCS): Remove _xmulhisi3_exit.
    Add _muluhisi3, _mulshisi3, _usmulhisi3.
    * config/avr/libgcc.S (__mulsi3): Rewrite.
    (__mulhisi3): Rewrite.
    (__umulhisi3): Rewrite.
    (__usmulhisi3): New.
    (__muluhisi3): New.
    (__mulshisi3): New.
    (__mulohisi3): New.
    (__mulqi3, __mulqihi3, __umulqihi3, __mulhi3): Use DEFUN/ENDF to
    declare.
    * config/avr/predicates.md (pseudo_register_operand): Rewrite.
    (pseudo_register_or_const_int_operand): New.
    (combine_pseudo_register_operand): New.
    (u16_operand): New.
    (s16_operand): New.
    (o16_operand): New.
    * config/avr/avr.c (avr_rtx_costs): Handle costs for mult:SI.
    * config/avr/avr.md (QIHI, QIHI2): New mode iterators.
    (any_extend, any_extend2): New code iterators.
    (extend_prefix): New code attribute.
    (mulsi3): Rewrite. Turn insn to expander.
    (mulhisi3): Ditto.
    (umulhisi3): Ditto.
    (usmulhisi3): New expander.
    (*mulsi3): New insn-and-split.
    (mulu<mode>si3): New insn-and-split.
    (muls<mode>si3): New insn-and-split.
    (mulohisi3): New insn-and-split.
    (*uumulqihisi3, *uumulhiqisi3, *uumulhihisi3, *uumulqiqisi3,
    *usmulqihisi3, *usmulhiqisi3, *usmulhihisi3, *usmulqiqisi3,
    *sumulqihisi3, *sumulhiqisi3, *sumulhihisi3, *sumulqiqisi3,
    *ssmulqihisi3, *ssmulhiqisi3, *ssmulhihisi3, *ssmulqiqisi3): New
    insn-and-split.
    (*mulsi3_call): Rewrite.
    (*mulhisi3_call): Rewrite.
    (*umulhisi3_call): Rewrite.
    (*usmulhisi3_call): New insn.
    (*muluhisi3_call): New insn.
    (*mulshisi3_call): New insn.
    (*mulohisi3_call): New insn.
    (extendqihi2): Use combine_pseudo_register_operand as predicate
    for operand 1.
    (extendqisi2): Ditto.
    (zero_extendqihi2): Ditto.
    (zero_extendqisi2): Ditto.
    (zero_extendhisi2): Ditto.
    (extendhisi2): Ditto. Don't early-clobber operand 0.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/avr/avr.c
    trunk/gcc/config/avr/avr.md
    trunk/gcc/config/avr/libgcc.S
    trunk/gcc/config/avr/predicates.md
    trunk/gcc/config/avr/t-avr

[Bug target/49687] [4.6 Regression][avr] Missed optimization for widening MUL

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

--- Comment #6 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-29 11:27:45 UTC ---
Author: gjl
Date: Fri Jul 29 11:27:39 2011
New Revision: 176923

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=176923
Log:

    PR target/49687
    * config/avr/avr.md (mulsi3, *mulsi3, mulu<mode>si3,
    muls<mode>si3, mulohisi3, mulhisi3, umulhisi3, usmulhisi3,
   
*<any_extend:extend_prefix><any_extend2:extend_prefix>mul<QIHI:mode><QIHI2:mode>si3):
    Add X to register footprint: Clobber r26/r27.


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

[Bug target/49687] [4.6 Regression][avr] Missed optimization for widening MUL

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

--- Comment #7 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-29 11:49:30 UTC ---
With this milestone the work for better support for widening multiplication is
finished -- fir the case when MUL instruction is available.

Similar work for the case when no hardware multiplier is available needs still
to be done.

The preferred approach in that case is to do the extension explicitely in
libgcc prior to the multiplication.  Respective code was already included in
libgcc but dead because no one calls it up to now.

[Bug target/49687] [4.6 Regression][avr] Missed optimization for widening MUL

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

--- Comment #8 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-08-11 07:50:42 UTC ---
Author: gjl
Date: Thu Aug 11 07:50:37 2011
New Revision: 177648

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=177648
Log:

    PR target/49687
    * config/avr/avr.md (smulqi3_highpart): New insn.
    (umulqi3_highpart): New insn.
    (*subqi3.ashiftrt7): New insn.
    (smulhi3_highpart): New expander.
    (umulhi3_highpart): Nex expander.
    (*smulhi3_highpart_call): New insn.
    (*umulhi3_highpart_call): New insn.
    (extend_u): New code attribute.
    (extend_prefix): Rename code attribute to extend_su.
    * config/avr/avr.c (avr_rtx_costs): Report costs of highpart of
    widening QI/HI multiply.


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

[Bug target/49687] [4.6 Regression][avr] Missed optimization for widening MUL

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hennebry at web dot
                   |                            |cs.ndsu.nodak.edu

--- Comment #9 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-08-11 21:43:47 UTC ---
*** Bug 39250 has been marked as a duplicate of this bug. ***

[Bug target/49687] [4.6 Regression][avr] Missed optimization for widening MUL

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687

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

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

--- Comment #10 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-09-09 17:57:34 UTC ---
Closed for the 4.7.0 Milestone.