A simple function that just sums over a vector is much slower if inlined than
out of line. The o-o-l version keeps the sum in a xmm register, the inline
version keeps reading and storing the stack variable on each iteration (guessed
looking at the assembler).
Timings on a 2.4 P4 Xeon:
out-of line:
T0: 3117.44 ms
T1: 653.93 ms
inline:
T0: 3097.05 ms
T1: 3104.18 ms
--
Summary: Inline code performance much worse than out-of-line
Product: gcc
Version: 4.1.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jamagallon at ono dot com
GCC target triplet: i586-mandriva-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31396
