------- Comment #2 from christophe dot jaillet at wanadoo dot fr 2006-07-14
21:11 -------
I tried to compile it on my cygwin box and had a strange (and certainly
unrelated) behaviour :
gcc -O3 test.c -S
Version 3.4.4 (must be the latest version available on cygwin :()
Description : the case 1 is tested in two times. First <=2 then == 1. I think
that it is useless and that if
cmpl $2, %ebx
jle L9
was turned into
cmpl $1,%ebx
je L9
the second test after L9: would be useless.
See code below.
.file "test.c"
.def ___main; .scl 2; .type 32; .endef
.text
.p2align 4,,15
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl $16, %eax
movl %esp, %ebp
pushl %ebx
subl $4, %esp
andl $-16, %esp
call __alloca
call ___main
cmpl $2, %ebx
je L4
cmpl $2, %ebx
jle L9 ==> every thing <= 2
cmpl $3, %ebx
je L10
L6:
movb $13, (%ebx)
xorl %eax, %eax
movb $13, 1(%ebx)
movb $13, 2(%ebx)
movb $13, 3(%ebx)
movl -4(%ebp), %ebx
leave
ret
.p2align 4,,7
L9:
cmpl $1, %ebx ==> Now comparaison against 1 is done !
jne L6
movb $13, (%ebx)
xorl %eax, %eax
movl -4(%ebp), %ebx
leave
ret
.p2align 4,,7
L4:
movb $13, (%ebx)
xorl %eax, %eax
movb $13, 1(%ebx)
movl -4(%ebp), %ebx
leave
ret
.p2align 4,,7
L10:
movb $13, (%ebx)
xorl %eax, %eax
movb $13, 1(%ebx)
movb $13, 2(%ebx)
movl -4(%ebp), %ebx
leave
ret
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11832
