[Bug target/36467] New: [avr] Missed optimization with pointer arithmetic and mul*

[Bug target/36467] New: [avr] Missed optimization with pointer arithmetic and mul*

[eric dot weddington at atmel dot com]

>From AVR Freaks forum:
http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&p=453770#453770

Adding an offset to a pointer to a structure. If the structure size is 16, the
generated code is a loop with shifts. If the structure size is 17, the
generated code uses MUL* instructions and generates shorter code than when the
size is 16.

Command lines:
avr-gcc -save-temps -Os -mmcu=atmega32 -c test.c -o test.o
avr-gcc -save-temps -Os -mmcu=atmega32 -c test2.c -o test2.o

See the code generation of funct().

Test cases to follow...


-- 
           Summary: [avr] Missed optimization with pointer arithmetic and
                    mul*
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: eric dot weddington at atmel dot com
GCC target triplet: avr-*-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36467

[Bug target/36467] [avr] Missed optimization with pointer arithmetic and mul*

[eric dot weddington at atmel dot com]

------- Comment #1 from eric dot weddington at atmel dot com  2008-06-08 17:57 -------
Created an attachment (id=15734)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15734&action=view)
Test case with structure size == 16.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36467

[Bug target/36467] [avr] Missed optimization with pointer arithmetic and mul*

[eric dot weddington at atmel dot com]

------- Comment #2 from eric dot weddington at atmel dot com  2008-06-08 17:58 -------
Created an attachment (id=15735)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15735&action=view)
Test case with structure size == 17.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36467

[Bug target/36467] [avr] Missed optimization with pointer arithmetic and mul*

[eric dot weddington at atmel dot com]

------- Comment #3 from eric dot weddington at atmel dot com  2008-06-08 18:08 -------
Generated code when structure size is 16 (test.i):

funct:
/* prologue: function */
/* frame size = 0 */
        lds r24,head
        mov r30,r24
        clr r31
        sbrc r30,7
        com r31
        ldi r24,4
1:      lsl r30
        rol r31
        dec r24
        brne 1b
        subi r30,lo8(-(qq))
        sbci r31,hi8(-(qq))
        ld r24,Z
        sbrc r24,1
        std Z+1,__zero_reg__
.L3:
        ret


Generated code when structure size is 17 (test2.i):

funct:
/* prologue: function */
/* frame size = 0 */
        lds r24,head
        ldi r25,lo8(17)
        muls r24,r25
        movw r30,r0
        clr r1
        subi r30,lo8(-(qq))
        sbci r31,hi8(-(qq))
        ld r24,Z
        sbrc r24,1
        std Z+1,__zero_reg__
.L3:
        ret


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36467

[Bug target/36467] [avr] Missed optimization with pointer arithmetic and mul*

[hutchinsonandy at gcc dot gnu dot org]

------- Comment #4 from hutchinsonandy at gcc dot gnu dot org  2008-06-08 18:20 -------
It makes sense in one respect
We don't have fast shift by 4 bits and code defaults to loop for Os. Seems we
should be selective as MUL is indeed shorter.

Though I think gcc may be confused by our poor cost data and perhaps was alsp
mislead into using shift instead of MUL.


-- 

hutchinsonandy at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-06-08 18:20:52
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36467

[Bug target/36467] [avr] Missed optimization with pointer arithmetic and mul*

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36467

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

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

--- Comment #7 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-20 17:26:03 UTC ---
Closed as FIXED: Reworked (widening) 16-bit multiply.

[Bug target/36467] [avr] Missed optimization with pointer arithmetic and mul*

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36467

--- Comment #6 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/36467] [avr] Missed optimization with pointer arithmetic and mul*

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36467

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2008-06-08 18:20:52         |2011-07-09 18:20:52
                 CC|                            |gjl at gcc dot gnu.org
   Target Milestone|---                         |4.7.0
      Known to fail|                            |4.6.1

[Bug target/36467] [avr] Missed optimization with pointer arithmetic and mul*

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36467

--- Comment #5 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-09 09:10:56 UTC ---
Created attachment 24723
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24723
Extendedn test case with size = 15, 16, 17, 18