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Re: volatile [was: GCC warnings for unused global variables]
Fergus Henderson <fjh@cs.mu.oz.au> writes:
| On 04-May-2003, Gabriel Dos Reis <gdr@integrable-solutions.net> wrote:
| > Fergus Henderson <fjh@cs.mu.oz.au> writes:
| > | I do not agree that the text which you quoted permitted such optimization.
| >
| > Still, it says so in black on white.
|
| The C standard text which you quoted doesn't say that the optimization
| is permitted unconditionally.
^^^^^^^^^^^^^^^
Which is not my claim.
| It only says that the optimization is
| permitted only "if [the implementation] can deduce that [the expression's]
| value is not used and that no needed side effects are produced".
In what is that different from
# Why? the last part of the paragraph quoted above does specifically
# permit that optimization where applicable.
quoted from http://gcc.gnu.org/ml/gcc/2003-05/msg00145.html ?
| In the
| case of volatile variables, this condition is always false,
No, because the standard does specifically add
INCLUDING ANY CAUSED BY CALLING A FUNCTION OR ACCESSING A VOLATILE
OBJECT
| because the
| definition of volatile means that the implementation can never know if
| a side effect is "needed".
The definition of "volatile" does not say that the implementation can
never know if a side effect is needed. what you've discovered is just
another facet of the ill-defined notion of "volatile".
-- Gaby