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gcc -O3 & gprof
From: |
Alex Vinokur |
Subject: |
gcc -O3 & gprof |
Date: |
Mon, 17 Mar 2003 14:00:29 +0200 |
=====================
Windows 2000
DJGPP 2.03
GNU gcc version 3.2.1
GNU gprof 2.13
=====================
Here is a simple program that has been profiled with using gprof.
We can see that if the program is compiled with option -O3
then gprof's output doesn't contained called functions foo1() and foo2().
Any explanation ?
========= C code : BEGIN =========
/* File main.c */
int foo1 (int argc) { return argc; }
int foo2 (int argc) { return argc; }
int main(int argc)
{
return (foo1(argc) + foo2(argc));
}
========= C code : END ===========
========= Compiling & Running : BEGIN =========
% gcc -o a0.exe main.c -g -pg
% a0.exe
% gprof -b a0.exe
Flat profile:
Each sample counts as 0.0555556 seconds.
no time accumulated
% cumulative self self total
time seconds seconds calls Ts/call Ts/call name
0.00 0.00 0.00 1 0.00 0.00 foo1
0.00 0.00 0.00 1 0.00 0.00 foo2
0.00 0.00 0.00 1 0.00 0.00 main
[---omitted---]
-----------------------------------------------
% gcc -O1 -o a1.exe main.c -g -pg
% a1.exe
% gprof -b a1.exe
Flat profile:
Each sample counts as 0.0555556 seconds.
no time accumulated
% cumulative self self total
time seconds seconds calls Ts/call Ts/call name
0.00 0.00 0.00 1 0.00 0.00 foo1
0.00 0.00 0.00 1 0.00 0.00 foo2
0.00 0.00 0.00 1 0.00 0.00 main
[---omitted---]
-----------------------------------------------
% gcc -O2 -o a2.exe main.c -g -pg
% a2.exe
% gprof -b a2.exe
Flat profile:
Each sample counts as 0.0555556 seconds.
no time accumulated
% cumulative self self total
time seconds seconds calls Ts/call Ts/call name
0.00 0.00 0.00 1 0.00 0.00 foo1
0.00 0.00 0.00 1 0.00 0.00 foo2
0.00 0.00 0.00 1 0.00 0.00 main
[---omitted---]
-----------------------------------------------
% gcc -O3 -o a3.exe main.c -g -pg
% a3.exe
% gprof -b a3.exe
Flat profile:
Each sample counts as 0.0555556 seconds.
no time accumulated
% cumulative self self total
time seconds seconds calls Ts/call Ts/call name
0.00 0.00 0.00 1 0.00 0.00 main
[---omitted---]
========= Compiling & Running : END ===========
=================================
Alex Vinokur
mailto:alexvn@connect.to
http://www.simtel.net/pub/oth/19088.html
=================================
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