http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44382
William J. Schmidt <wschmidt at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |wschmidt at gcc dot gnu.org
--- Comment #7 from William J. Schmidt <wschmidt at gcc dot gnu.org> 2011-07-12
17:33:06 UTC ---
The test case from bug 45671 is as follows:
int myfunction (int a, int b, int c, int d, int e, int f, int g, int h) {
int ret;
ret = a + b + c + d + e + f + g + h;
return ret;
}
Compiling with -O3 results in a series of dependent add instructions to
accumulate the sum.
add 4,3,4
add 4,4,5
add 4,4,6
add 4,4,7
add 4,4,8
add 4,4,9
add 4,4,10
If we regrouped to (a+b)+(c+d)+... we can do multiple adds in parallel on
different execution units.
