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Re: volatile and R/M/W operations
Richard Kenner wrote:
OK, sounds reasonable, but then I don't understand the logic behind
avoiding this instruction sequence for the volatile case, this is
two accesses at the bus level so what's the difference?
There's no difference from that perspective. The logic behind what's
generated is that instead of trying to do a case-by-case analysis of
what instruction combinations might actually be valid for volatile
memory (which could potentially be target-specific), GCC takes the
conservative approach of simply disabling all but trivial combinations
for volatile access.
Right, but it would seem this is a good canididate for combination. This
is especially true since often Volatile is used with the sense of Atomic
in Ada, and it is not a bad idea to combine these in practice, giving an
atomic update (right, nothing in the language requires it, but it is
definitely useful!)