Re: spin_lock forgets to clobber memory and other smp fixes [was

[Andrea Arcangeli]

On Thu, 7 Sep 2000, Jamie Lokier wrote:

>Common Subexpression Elimination.
>
>If the compiler sees an expression equivalent to one it evaluated
>earlier, there is no need to evaluate it a second time.
>
>So "a = x+x; b = x+x" will evaluate "x+x" just once and store it twice.

I didn't know the name of that particular optimization, thanks.

>In more complicated cases, where the result of the first read is
>actually used before the "asm", the "memory" clobber causes the second
>read to occur as well as the first.

Indeed.

Andrea

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