------- Additional Comments From vda at port dot imtp dot ilyichevsk dot odessa
dot ua 2005-04-24 13:05 -------
With 4.0.0: gcc -O2 gives the same result as gcc -O3,
which is better than gcc 3.4.3 -O2 but worse than 3.4.3 -O3.
For example:
movl %edx, -20(%ebp)
orl %ecx, %edi
movl %ebx, %esi
xorl %ecx, %esi
andl %eax, %ebx
xorl %edi, %ebx
movl %eax, %ecx
notl %ecx
xorl %ebx, %ecx
orl %edi, %eax
xorl %eax, %esi
rorl $19, %esi
rorl $29, -20(%ebp)
xorl %esi, %ebx
xorl -20(%ebp), %ecx
xorl -20(%ebp), %ebx
rorl $31, %ebx
leal 0(,%esi,8), %edx
1) Why %edx was stored in -20(%ebp), there is no %edx usage
in the following insns. %edx value could stay in register
and we can continue to work on its value in register.
2) rorl $31, %ebx == roll $1, %ebx, but 1 bit roll insn is
smaller.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21182
