From:	Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: -O3 doesnt remove dead code
Date:	14 Sep 2002 17:34:17 GMT
Organization:	Aachen University of Technology (RWTH)
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Rafal 'Raf256' Maj <rafal AT raf256 DOT com> wrote:
> Hello,
> Following program compield with -03 does NOT had dead-code loop removed. 
> This empty loop actualy IS executed (and program takes few seconds to 
> complete)

> int main() { for (long long int i=0; i<500000000; i++) ; return 0; } 

> IMHO compiler at -O3 should optimize code to :

> int main() { 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.

-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.

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