[Bug c++/59845] New: loop optimization problem when profiling
arshamidi at gmail dot com
gcc-bugzilla@gcc.gnu.org
Thu Jan 16 18:12:00 GMT 2014
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59845
Bug ID: 59845
Summary: loop optimization problem when profiling
Product: gcc
Version: 4.8.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: arshamidi at gmail dot com
I'm using g++ with GCC 4.8.1; when I use fprofile-generate too optimize my
code, it actually slows down the process time: (constant folding problem within
loop?)
int main(){
int n;
int i;
//int n2;
printf("Enter a number: ");
scanf("%d", &n);
//n2 = n/2;
printf("divisors are:\n\n");
for (i=1; i <= /*n2*/ n/2; i++)
if (n%i == 0)
printf("\n%d", i);
printf("\n\n end.\n");
return 0;
}
Here I must use the constant 'n2' (commented out) too actually get the desired
speed -in combination with -fprofile-generate.
I'm using the following switches:
-Ofast;-fomit-frame-pointer;-march=core2; -mfpmath=sse; -fprofile-generate;
-Wall
no problem without -fprofile-generate and -fprofile-use
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