[Bug target/28481] [4.2/4.3/4.4 Regression] regression from 3.x: 4.1.1 uses memory where it can use registers

[vda dot linux at googlemail dot com]

------- Comment #9 from vda dot linux at googlemail dot com  2008-07-04 20:48 -------
The above comment meant to say "4.3.1 have number of memory references down
from 115 _to 48_.

I also attached the best result so far - gcc-3.4.6 with -O3 genarates assembly
with smallest number of memory references. Here is more correct method of
counting them (counting not only moves, but any memory references (XOR insns),
but not counting LEA instructions which aren't memory references):

# grep '(' serpent-346-O3.s | grep -v lea | wc -l
144
# grep '(' serpent-431-O3.s | grep -v lea | wc -l
186

Another way to see that 3.4.6 -O3 is optimal is to notice the lack of "subl
$NUM, %esp" in prologue (because gcc figured out it does not need to spill any
registers):

serpent_encrypt:
        pushl   %ebp
        pushl   %edi
        pushl   %esi
        pushl   %ebx
        movl    20(%esp), %ebp
        movl    28(%esp), %ecx
        movl    12(%ebp), %edi
        xorl    12(%ecx), %edi
...

4.3.1 looks like this:

serpent_encrypt:
        pushl   %ebp
        pushl   %edi
        pushl   %esi
        pushl   %ebx
        subl    $20, %esp
        movl    48(%esp), %eax
        movl    (%eax), %ecx
        movl    4(%eax), %edx
        movl    8(%eax), %esi
...


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28481