------- Comment #2 from mlitwack at employees dot org 2007-03-31 15:45 -------
Subject: Re: avr-gcc wrongly optimizes bit sets/resets
for IO register 0x20
Hi Eric,
Indeed, the test program works for me too under GCC 4.1.2. However, I
am developing on the ATtiny24 and 44, which isn't supported in GCC 4.1.x
(-mmcu=attiny24 and friends). That's why I was using the 4.2
pre-release.
The test program still generates bad code under a more recent
pre-release (gcc-core-4.2.0-20070316) (I do check periodically).
Although not a critical bug since there are plenty of ways to work
around it, I was hoping to head it off now before 4.2.0 made it to
release.
It might be worth noting that the more generic -mmcu=avr2 also causes
the pre-release to generate bad code for I/O register 0x20.
Below is more detail on what's happening.
Thanks,
-mark
On Fri, 2007-03-30 at 19:58 +0000, eweddington at cso dot atmel dot com
wrote:
>
> ------- Comment #1 from eweddington at cso dot atmel dot com 2007-03-30
> 20:58 -------
> The test program works for me for AVR GCC 4.1.1. (WinAVR distro 20070122)
>
>
----------------------------------------------
File gcc-sbi-bug.c:
typedef unsigned char uint8_t;
#define _MMIO_BYTE(mem_addr) (*(volatile uint8_t *)(mem_addr))
#define _SFR_IO8(io_addr) _MMIO_BYTE((io_addr) + 0x20)
#define PCMSK1 _SFR_IO8(0x20)
main()
{
PCMSK1 |= 0x01;
}
----------------------------------------------
Code generated by gcc-core-4.2.0-20070316
(avr-gcc -Os -S gcc-sbi-bug.c -mmcu=attiny44):
.file "gcc-sbi-bug.c"
__SREG__ = 0x3f
__SP_H__ = 0x3e
__SP_L__ = 0x3d
__tmp_reg__ = 0
__zero_reg__ = 1
.global __do_copy_data
.global __do_clear_bss
.text
.global main
.type main, @function
main:
/* prologue: frame size=0 */
ldi r28,lo8(__stack - 0)
ldi r29,hi8(__stack - 0)
out __SP_H__,r29
out __SP_L__,r28
/* prologue end (size=4) */
sbi 64-0x20,0 <----- WRONG!
/* epilogue: frame size=0 */
rjmp exit
/* epilogue end (size=1) */
/* function main size 6 (1) */
.size main, .-main
/* File "gcc-sbi-bug.c": code 6 = 0x0006 ( 1), prologues 4,
epilogues 1 */
----------------------------------------------
Code generated by gcc-4.1.2:
(avr-gcc -Os -S gcc-sbi-bug.c):
.file "gcc-sbi-bug.c"
.arch avr2
__SREG__ = 0x3f
__SP_H__ = 0x3e
__SP_L__ = 0x3d
__tmp_reg__ = 0
__zero_reg__ = 1
.global __do_copy_data
.global __do_clear_bss
.text
.global main
.type main, @function
main:
/* prologue: frame size=0 */
ldi r28,lo8(__stack - 0)
ldi r29,hi8(__stack - 0)
out __SP_H__,r29
out __SP_L__,r28
/* prologue end (size=4) */
in r24,64-0x20 <----- OK
ori r24,lo8(1) <-----
out 64-0x20,r24 <-----
/* epilogue: frame size=0 */
rjmp exit
/* epilogue end (size=1) */
/* function main size 8 (3) */
.size main, .-main
/* File "gcc-sbi-bug.c": code 8 = 0x0008 ( 3), prologues 4,
epilogues 1 */
----------------------------------------------
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29932
