------- Comment #3 from jacob at math dot jussieu dot fr 2008-02-27 15:49
-------
Thank you for the quick reply. I'm glad to hear that it's fixed and much
improved in 4.3.
I tried what you said about __attribute__((flatten)) (I copied and pasted your
code) and that didn't change the performance at all (with 4.2.3). I compiled
with
g++ -O3 -DDEPTH18 test.cpp -S -o test.s
and the generated assembly file starts as follows:
.file "test.cpp"
.section .ctors,"aw",@progbits
.align 4
.long _GLOBAL__I__Z8evaluatev
.text
.align 2
.p2align 4,,15
.globl _Z8evaluatev
.type _Z8evaluatev, @function
_Z8evaluatev:
.LFB1436:
pushl %ebp
.LCFI0:
movl %esp, %ebp
.LCFI1:
pushl %edi
.LCFI2:
pushl %esi
.LCFI3:
xorl %esi, %esi
pushl %ebx
.LCFI4:
xorl %ebx, %ebx
subl $172, %esp
.LCFI5:
leal -84(%ebp), %edi
.p2align 4,,7
.L2:
leal -160(%ebp), %eax
movl %ebx, -16(%ebp)
movl %ebx, -20(%ebp)
movl %ebx, -24(%ebp)
movl %ebx, -28(%ebp)
movl %ebx, -32(%ebp)
movl %ebx, -36(%ebp)
movl %ebx, -40(%ebp)
movl %ebx, -44(%ebp)
movl %ebx, -48(%ebp)
movl %ebx, -52(%ebp)
movl %ebx, -56(%ebp)
movl %ebx, -60(%ebp)
movl %ebx, -64(%ebp)
movl %ebx, -68(%ebp)
movl %ebx, -72(%ebp)
movl %ebx, -76(%ebp)
movl %ebx, -80(%ebp)
movl %ebx, -84(%ebp)
movl $72, 8(%esp)
movl %edi, 4(%esp)
movl %eax, (%esp)
call memcpy
movl -92(%ebp), %eax
addl -96(%ebp), %eax
addl -100(%ebp), %eax
addl -104(%ebp), %eax
addl -108(%ebp), %eax
addl -112(%ebp), %eax
addl -116(%ebp), %eax
addl -120(%ebp), %eax
addl -124(%ebp), %eax
addl -128(%ebp), %eax
addl -132(%ebp), %eax
addl -136(%ebp), %eax
addl -140(%ebp), %eax
addl -144(%ebp), %eax
addl -148(%ebp), %eax
addl -152(%ebp), %eax
addl -156(%ebp), %eax
addl -160(%ebp), %eax
addl %esi, %eax
leal (%eax,%ebx), %esi
addl $1, %ebx
cmpl $1000000000, %ebx
jne .L2
addl $172, %esp
movl %esi, %eax
popl %ebx
popl %esi
popl %edi
popl %ebp
ret
.LFE1436:
.size _Z8evaluatev, .-_Z8evaluatev
As you can see, there is a call to memcpy() which isn't present in your
version. What can I do (if anything) to improve speed with g++ 4.2.3?
Also, isn't it a bit surprising to have a call in a function that has
__attribute__((flatten)) ? The compilation doesn't produce any warning.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35393
