Re: GCC 3.3 code generation error

[Andrew Pinski <pinskia at physics dot uc dot edu>]

Please file a bug report but I still see it on the mainline ().
Also Here is a workaround:
void flash_wait_ready(volatile unsigned *vaddr)
{
        while(1)
        {
                unsigned temp = *vaddr;
                if (temp != *vaddr)
                        break;
        }
}

Thanks,
Andrew Pinski


On Monday, Jun 30, 2003, at 11:50 US/Eastern, Tobias Ringstrom wrote:

> Example code:
>
> void
> flash_wait_ready(volatile unsigned *vaddr)
> {
> 	while (*vaddr != *vaddr)
> 		;
> }
>
> Using gcc 3.3 (tested with arm-elf and i686-pc-linux-gnu), the loop in 
> the example above is incorrectly removed by the optimizer when using 
> -O. Correct code is generated using -O2, -O3 and -Os. Here is the -O 
> case:
>
> > gcc -S -o - -O tmp.c
> 	.file	"tmp.c"
> 	.text
> .globl flash_wait_ready
> 	.type	flash_wait_ready, @function
> flash_wait_ready:
> 	pushl	%ebp
> 	movl	%esp, %ebp
> 	popl	%ebp
> 	ret
> 	.size	flash_wait_ready, .-flash_wait_ready
> 	.ident	"GCC: (GNU) 3.3"
> >
>
> It's a regression from GCC 3.2.3 which generates correct code with -O.
>
> [I know the code looks funny, but as the function name indicates I'm 
> waiting for a flash memory to finish. When the flash is busy, two 
> consecutive read accesses will not read the same value.]
>
> /Tobias