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As far as I understand it the compiler's break down the code into
abstract syntax graphs then use a number of graph optimizations to
reduce it into an optimized state. The examples will almost certainly
produce equivalent binary output.
Rather than being concerned about how best to help the compiler
optimize I usually worry about the most understandable way to write
the function. Compilers are really, really good at their job, and the
completely unoptimized version is the one your going to see when you
are debugging -O0 builds.
- -Jesse
On 6/3/2012 02:38, Krzysztof wrote:
> Let's have a below code:
>
> struct st { int iv; /*...*/ };
>
> void afun(struct st *stp) { stp->iv++; printf("%d\n",stp->iv); }
>
> Is it helpful for a compiler to do better optimization if I write
> the function as this?
>
> void afun(struct st *stp) { int liv=stp->iv++;
>
> printf("%d\n",liv); }
>
> In other words, is it better from optimization point of view to do
> assignments structure members values to local variables then do
> what you need to and then assign them back to member variables?
>
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