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* [Bug c/38629]  New: gcc version 4.2.x, 4.3.x and 4.4.0 are doing (too much) automatic inlining with -O1, -O2 and -Os
@ 2008-12-26 14:58 cbm at d81 dot de
  2008-12-26 15:41 ` [Bug target/38629] target-specific parameters for inline heuristics not defined for AVR steven at gcc dot gnu dot org
                   ` (3 more replies)
  0 siblings, 4 replies; 8+ messages in thread
From: cbm at d81 dot de @ 2008-12-26 14:58 UTC (permalink / raw)
  To: gcc-bugs

Hello GCC bug hunters,

I'm using GCC C compiler, compiled as a cross compiler for AVR (ATmel
microcontrollers) on Cygwin (Windows). With earlier GCC version 4.1.2 always
smaller code was generated for one of the projects I'm working on than with
more recent versions of GCC. I tested with GCC 4.2.x a while ago and more
recently with GCC 4.3.3 (snapshot) and GCC 4.4 (snapshot also).

Since I'm mostly adding patches to GCC from the WinAVR project, I prepared a
freshly compiled GCC 4.3.3 (20081219) without these patches for this bug report
over here. The following is the version output of the compiler for my tests:

#> avr-gcc43 -v
Using built-in specs.
Target: avr
Configured with: ../gcc-4.3-20081218/configure --prefix=/usr/local --target=avr
--program-prefix=avr- --program-suffix=43 --enable-languages=c --disable-libssp
Thread model: single
gcc version 4.3.3 20081218 (prerelease) (GCC) 


Failure description:
GCC 4.3.3 does automatically inline (many) functions, when optimization setting
"-O2" is used. It even inlines static functions that are called several times
from all over the code within the same module. This heavily increases code
size.
Even worse, this code blowing automatic inline is also done with optimzation
setting "-Os" and therefore contradicts this optimization setting. With
GCC-4.1.2 this code increase because of (too much) automatic function inlining
could not be observed, although even GCC-4.1.2 does some automatic inlining.

Here's a stripped down code sample to demonstrate the bug:

/*
 * License: GPL
 * Copyright: (c) 2007 by Till Harbaum <till@harbaum.org>
 * Copyright: (c) 2008 Wolfgang Moser, http://d81.de
 */

/* #include <avr/wdt.h> */
/* some declarations from the include above for ATMega8 */
#define _SFR_IO8(io_addr) (*(volatile unsigned char *)((io_addr) + 0x20))
#define TOV0    0
#define TCNT0   _SFR_IO8(0x32)
#define TIFR    _SFR_IO8(0x38)
#define DDRC    _SFR_IO8(0x14)
#define DDRD    _SFR_IO8(0x11)
#define PORTC   _SFR_IO8(0x15)
#define PORTD   _SFR_IO8(0x12)

static void delay_wait_us( unsigned char timeout ) {
        __asm__ __volatile__ ("wdr");

        TCNT0 = timeout;
        TIFR |= (1 << (TOV0));

        /* wait until counter overflows */
        while(!(TIFR & (1 << (TOV0))));
}

static void delay_wait_us_ms( unsigned char timeout ) {
        delay_wait_us( timeout * 1000 );
}


void makeUseOfTimerWait( unsigned char val ) {
        delay_wait_us( 10 );
        DDRC |= 0x10;
        delay_wait_us( 10 );
        DDRD |= 0x20;

        delay_wait_us( 20 );
        PORTC &= ~0x10;
        delay_wait_us( 10 );
        PORTD &= ~0x20;

        delay_wait_us_ms( 5 );

        PORTC |= val & 0x10;
        delay_wait_us( 10 );
        PORTD |= val & 0x20;

        delay_wait_us( 10 );
}

Compiling this sample with: #> avr-gcc43 -save-temps -c -Wall -Os -mmcu=atmega8
autoinline.c
leads to the following module components: #> avr-nm -S --size-sort autoinline.o
00000000 0000009c T makeUseOfTimerWait

Both static functions, delay_wait_us() as well as delay_wait_ms() were inlined,
although the GCC manual clearly states that automatic function inlining would
only be enabled for optimization "-O3" of greater.

Normally, when optimizing for size with "-Os" (but also, when using "-O1" or
"-O2"), at least I would expect that at most functions are inlined that do not
increase code size. For the example above and setting "-Os", function
delay_wait_ms() may be inlined, because it is used only once. But function
delay_wait_us() must not be inlined. This behavior could be provoked by setting
special GCC internal configuration parameters like e.g.:

#> avr-gcc43 -save-temps --param max-inline-insns-auto=4 -c -Wall -Os
-mmcu=atmega8 autoinline.c

#> avr-nm -S --size-sort autoinline.o                                          
             00000000 00000012 t delay_wait_us
00000012 0000003e T makeUseOfTimerWait

That way code size reduce to 0x12+0x3e=0x50 instead of 0x9c (only taking
function symbols into account).


With kind regards, Wolfgang Moser


-- 
           Summary: gcc version 4.2.x, 4.3.x and 4.4.0 are doing (too much)
                    automatic inlining with -O1, -O2 and -Os
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: cbm at d81 dot de
 GCC build triplet: i386/cygwin
  GCC host triplet: i386/cygwin
GCC target triplet: avr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38629


^ permalink raw reply	[flat|nested] 8+ messages in thread
end of thread, other threads:[~2015-04-09 15:47 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
     [not found] <bug-38629-4@http.gcc.gnu.org/bugzilla/>
2010-11-10 20:19 ` [Bug target/38629] target-specific parameters for inline heuristics not defined for AVR hubicka at gcc dot gnu.org
2010-11-10 20:52 ` hubicka at gcc dot gnu.org
2015-04-09 15:43 ` federico at fsfe dot org
2015-04-09 15:47 ` federico at fsfe dot org
2008-12-26 14:58 [Bug c/38629] New: gcc version 4.2.x, 4.3.x and 4.4.0 are doing (too much) automatic inlining with -O1, -O2 and -Os cbm at d81 dot de
2008-12-26 15:41 ` [Bug target/38629] target-specific parameters for inline heuristics not defined for AVR steven at gcc dot gnu dot org
2008-12-26 21:30 ` forwards dot from dot bugzilla at d81 dot de
2008-12-26 21:36 ` pinskia at gcc dot gnu dot org
2008-12-29 20:14 ` rguenth at gcc dot gnu dot org

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