Re: -fno-tree-cselim not working?

[Ian Lance Taylor <iant at google dot com>]

Samuel Tardieu <sam@rfc1149.net> writes:

> #include <pthread.h>
> 
> static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
> static int acquires_count = 0;
> 
> int
> trylock()
> {
>   int res;
> 
>   res = pthread_mutex_trylock(&mutex);
>   if (res == 0)
>     ++acquires_count;
> 
>   return res;
> }
> 
> trylock:
>         subl    $12, %esp
>         movl    $mutex, (%esp)
>         call    pthread_mutex_trylock
>         movl    acquires_count, %edx
>         cmpl    $1, %eax
>         adcl    $0, %edx
>         movl    %edx, acquires_count
>         addl    $12, %esp
>         ret

By the way, since this is getting play on LKML and no doubt other
places:

This optimization (or pessimization, depending) is not new.  gcc 4.1
does the same thing.  The code has been in there since at least gcc
3.4, though I didn't build gcc 3.4 to test what happened.

Code like needs to use volatile or explicit memory barriers.

Ian