[Bug rtl-optimization/22563] [3.4/4.0/4.1 Regression] performance regression for gcc newer than 2.95

[dann at godzilla dot ics dot uci dot edu]

------- Additional Comments From dann at godzilla dot ics dot uci dot edu  2005-08-25 02:49 -------
This message:
http://gcc.gnu.org/ml/gcc/2005-08/msg00208.html

was asking for the reason for the slowdown for S000005e

AFAICT the inner loop for the benchmark (in s000005e_test) gets compiled to: 

.L153:
        fstl    (%edx)
        leal    8(%edx), %eax
        fstl    (%eax)
        fstl    8(%eax)
        fstl    16(%eax)
        fstl    24(%eax)
        fstl    32(%eax)
        fstl    40(%eax)
        fstl    48(%eax)
        leal    56(%eax), %edx
        cmpl    %edx, %ecx
        jne     .L153

and to:

.L9:
        movl    $0, (%edx)
        movl    $1074266112, 4(%edx)
        movl    $0, 8(%edx)
        movl    $1074266112, 12(%edx)
        movl    $0, 16(%edx)
        movl    $1074266112, 20(%edx)
        movl    $0, 24(%edx)
        movl    $1074266112, 28(%edx)
        movl    $0, 32(%edx)
        movl    $1074266112, 36(%edx)
        movl    $0, 40(%edx)
        movl    $1074266112, 44(%edx)
        movl    $0, 48(%edx)
        movl    $1074266112, 52(%edx)
        movl    $0, 56(%edx)
        movl    $1074266112, 60(%edx)
        addl    $64, %edx
        cmpl    %edx, %ebx
        jne     .L9

by 4.1

The 4.1 code looks much worse...

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22563