[Bug target/27593] bad code generation

[philipp at marek dot priv dot at]

--- Comment #8 from philipp at marek dot priv dot at  2006-05-16 08:20 
---
If I remove the -funroll-loops, will it cause better code generation? I.e.
only save two registers at function start, and use just these two registers?
Can I achieve such an optimization without doing assembly myself?

Thank you for your help!


Regards,

Phil


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27593

[Bug target/27593] bad code generation

[philipp at marek dot priv dot at]

--- Comment #6 from philipp at marek dot priv dot at  2006-05-15 05:17 
---
CFLAGS:=-g -mmcu=$(MCU) -Wall -Wstrict-prototypes -O2 -mcall-prologues
-I/usr/avr/include -I/home/flip/cprogs/AVR/include -funroll-loops -save-temps
%.s: %.c
$(CC) $(CFLAGS) -Os -S $

The .i results from the -save-temps (which I added for reporting this bug)


Regards,

Phil


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27593

[Bug c/27593] New: bad code generation

[philipp at marek dot priv dot at]

Hello,

I hope that I'm at the right place here.

I'm using debian gcc-avr:
Package: gcc-avr
Version: 1:4.1.0-1
-- System Information:
Debian Release: testing/unstable
  APT prefers testing
  APT policy: (850, 'testing'), (600, 'unstable'), (1, 'experimental')
Architecture: i386 (i686)
Shell:  /bin/sh linked to /bin/dash
Kernel: Linux 2.6.15-1-k7
Locale: LANG=de_AT, LC_CTYPE=de_AT (charmap=ISO-8859-1)

Versions of packages gcc-avr depends on:
ii  binutils-avr  2.16.1-1   Binary utilities that support Atme
ii  libc6 2.3.6-7GNU C Library: Shared libraries

gcc-avr recommends no packages.

-- no debconf information


This piece of code gets compiled incorrectly.
SIGNAL(SIG_INTERRUPT0)
{
   if (PIND  _BV(PD2))
   {
  low_period=TCNT1;
   }
   else
   {
  high_period=TCNT1;
   }
}


The result is:
SIGNAL(SIG_INTERRUPT0)
{
 294:   1f 92   pushr1
 296:   0f 92   pushr0
 298:   0f b6   in  r0, 0x3f; 63
 29a:   0f 92   pushr0
 29c:   11 24   eor r1, r1
 29e:   2f 93   pushr18
 2a0:   8f 93   pushr24
 2a2:   9f 93   pushr25
if (PIND  _BV(PD2))
 2a4:   4a 9b   sbis0x09, 2 ; 9
 2a6:   09 c0   rjmp.+18; 0x2ba __vector_1+0x26
{
// now H
high_period=TCNT1;
 2a8:   80 91 84 00 lds r24, 0x0084
 2ac:   90 91 85 00 lds r25, 0x0085
 2b0:   90 93 0c 01 sts 0x010C, r25
 2b4:   80 93 0b 01 sts 0x010B, r24
 2b8:   08 c0   rjmp.+16; 0x2ca __vector_1+0x36
}
else
{
low_period=TCNT1;
 2ba:   20 91 84 00 lds r18, 0x0084
 2be:   30 91 85 00 lds r19, 0x0085
 2c2:   30 93 0e 01 sts 0x010E, r19
 2c6:   20 93 0d 01 sts 0x010D, r18
 2ca:   9f 91   pop r25
 2cc:   8f 91   pop r24
 2ce:   2f 91   pop r18
 2d0:   0f 90   pop r0
 2d2:   0f be   out 0x3f, r0; 63
 2d4:   0f 90   pop r0
 2d6:   1f 90   pop r1
 2d8:   18 95   reti


- r0, r1 are pushed/popped, r1 is zeroed.
  If 0x3f really needs to be saved, it could be done by 
  another register, which has to be used anyway.
  (or instead of (r18, r19, r24, r25) (r0,r1) should be used.)
- r19 is modified, but not saved
- this whole construct could be optimized very much better.
- -Os, as already used, is much better than without. -O7 or -O2 
  give the same result as -Os.


Please see the attached files for details.

Thank you.


-- 
   Summary: bad code generation
   Product: gcc
   Version: 4.1.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: philipp at marek dot priv dot at
 GCC build triplet: i486-linux-gnu
  GCC host triplet: i486-linux-gnu
GCC target triplet: avr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27593

[Bug c/27593] bad code generation

[philipp at marek dot priv dot at]

--- Comment #1 from philipp at marek dot priv dot at  2006-05-13 20:09 
---
Created an attachment (id=11452)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11452action=view)
The C file


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27593

[Bug c/27593] bad code generation

[philipp at marek dot priv dot at]

--- Comment #2 from philipp at marek dot priv dot at  2006-05-13 20:09 
---
Created an attachment (id=11453)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11453action=view)
The Makefile


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27593

[Bug c/27593] bad code generation

[philipp at marek dot priv dot at]

--- Comment #3 from philipp at marek dot priv dot at  2006-05-13 20:10 
---
Created an attachment (id=11454)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11454action=view)
The preprocessor output


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27593

[Bug c/27593] bad code generation

[philipp at marek dot priv dot at]

--- Comment #4 from philipp at marek dot priv dot at  2006-05-13 20:11 
---
Created an attachment (id=11455)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11455action=view)
The output (dump) file


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27593