Date: Sun, 25 Apr 2010 21:02:43 +0300 From: Leonidas Tsampros <ltsampros@upnet.gr> To: yuri@rawbw.com Cc: freebsd-questions@freebsd.org Subject: Re: Why system gcc that is 4.2.1 produces different code than gcc-4.2.1 compiled from sources? Message-ID: <87k4rvh0l8.fsf@upnet.gr> In-Reply-To: <4BD3E923.9030606@rawbw.com> (yuri@rawbw.com's message of "Sun, 25 Apr 2010 00:02:59 -0700") References: <4BD3E923.9030606@rawbw.com>
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Yuri <yuri@rawbw.com> writes:
> I ran this simple example:
>
> #include <stdlib.h>
> #include <stdio.h>
>
> int fib(int AnArg) {
> if (AnArg <= 2) return (1);
> return (fib(AnArg-1)+fib(AnArg-2));
> }
>
> int main(int argc, char* argv[]) {
> int n = atoi(argv[1]);
> printf("fib(%i)=%i\n", n, fib(n));
> }
>
> through system gcc and gcc built from sources. Both are 4.2.1. Options: -O3.
>
> Average runtime with the argument 45 is quite different: system gcc is
> 3.650s and gcc-4.2.1 from sources is 3.740.
> CPU: Intel(R) Core(TM) i7 CPU @ 9200 @ 2.67GHz
>
Hi,
I'm pretty sure that a small difference in execution time does not mean
that the produced code is different. In order to check the code gcc
produced, you need to do something like this:
objdump -d executable
or even use gdb's disassemble command.
Regards,
Leonidas
> Yuri
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