[Bug c/31396] New: Inline code performance much worse than out-of-line

jamagallon at ono dot com gcc-bugzilla@gcc.gnu.org
Thu Mar 29 22:15:00 GMT 2007


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



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