From: "Rafal 'Raf256' Maj" <rafal AT raf256 DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: -O3 doesnt remove dead code
Date: 14 Sep 2002 17:55:42 GMT
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Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de> wrote in 
news:alvrup$25r$1 AT nets3 DOT rz DOT RWTH-Aachen DOT DE

>> int main() { for (long long int i=0; i<500000000; i++) ; return 0; } 
>> why this dead-loop is not removed ?

> Because the GCC people explicitly decided to not do that, IIRC.  The
> distinction being that a loop explicitly coded with an empty body is
> probably a timing-critical delay loop, and as such should be left
> alone.  If you put something into the loop, and try again, you just
> might see what you expected.

int a;
for (long long int i=0; i<500000000; i++) a=0;

gives same result :-/

IMHO time-critical loops should be marked as :

for (volatile long long int i=0; i<500000000; i++) ;
     ^^^^^^^^
this will never be optimized. And all dead codes should be deleted (this 
loop is not due to volatile counter)

Meybe I should report somwhere that 'bug' ? I use gcc 2.95 


-- 
Rafał 'Raf256' Maj
http://www.raf256.com