> Is there some kind of preprocessor line or something to instruct the
> optimizer to not optimize a certain section of code, but still be able
> to optimize the rest?
It isn't clear here what you mean by not optimizing. But assuming that the
order of the instructions is what bothers you, and also assuming a GNU
compiler collection (since you're posting on this mailing list), then you
can use a memory barrier or optimization barrier. Optimization barrier can
be done as follows:
volatile asm("":::"memory");
This tells the compiler to insert the assembly instruction (i.e. an empty
instruction). The "memory" part tells the compiler that this artificial
assembly instruction can alter the memory in some indirect way and the
volatile keyword is necessary so that the optimization doesn't remove the
empty instruction. The result will be that the compiler will make sure not
to mix the code before the asm directive with those that comes after it.
Notice that this doesn't prevent the processor from doing it's own
optimization, i.e. reordering instrcutions, but this seldom become a problem
for the program since the processor retirement unit will make sure to
produce the expected results. Usually instruction reordering on the
microprocessor scale is of interest to kernel developers only, and this is
where memory barriers becomes handy. If the previous assumption didn't match
what you had in mind, then feel free to reply with details of the
architecture and meaning of "not to optimize"
Cheers,
---------------------------
John V. Shahid
<[EMAIL PROTECTED]>
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