Re: [avr-gcc-list] Problem with delay loop

[Graham Davies]

Eric Weddington wrote:
> ... We were discussing the possibility of the
> compiler being smarter about 'volatile' and
> local automatic variables. I would definitely
> say that if the local variable's address is taken,
> then all bets are off.

Second point first.  If the address of a variable is taken then the compiler 
cannot put it in a register.  If it is declared automatic, it goes on the 
stack, if there is one, or somewhere else in memory if there isn't.  We put 
the address of variables on the stack into globals at our peril, but get 
away with it if we know what we're doing.  Nobody disagreed with any of 
this, but I thought it worth saying.

First point second.  I think I agree with you about the possibility of the 
compiler being really smart and figuring out that no way could a variable be 
seen outside of the local scope so to hell with it.  But, the standard 
doesn't take that approach so such a compiler would be non-standard.  I 
disagree with the people saying that the standard isn't very clear about 
what volatile means.  I think it's very clear.  A conforming compiler will 
never optimize away any access to a volatile variable.  Nor will it perform 
additional accesses, for example by using it to store intermediate values in 
a calculation.  I think the idea that the standard isn't clear comes from 
non-conforming compilers.

Graham.