PPC __arch_swab32 and __arch_swab16 generates non optimal code.
It doesn't schedule very well, need to copy its input register and
and swab16 needs an extra insn to clear its upper bits. I have improved
these functions(see my__xx). Any problem with the new asm? If
not I will send a patch.
Below some example code to illustrate:
#include <stdio.h>
unsigned long __arch_swab32(unsigned long value)
{
unsigned long result;
__asm__("rlwimi %0,%1,24,16,23\n\t"
"rlwimi %0,%1,8,8,15\n\t"
"rlwimi %0,%1,24,0,7"
: "=r" (result)
: "r" (value), "0" (value >> 24));
return result;
}
unsigned long my__arch_swab32(unsigned long value)
{
unsigned long tmp;
__asm__("rlwimi %0,%0,24,0xffffffff"
: "+r" (value));
__asm__("rlwinm %0,%1,16,0xffffffff"
: "=r" (tmp), "+r" (value));
__asm__("rlwimi %0,%1,0,0x00ff0000"
: "+r" (value), "+r" (tmp));
__asm__("rlwimi %0,%1,0,0x000000ff"
: "+r" (value), "+r" (tmp));
return value;
}
unsigned short __arch_swab16(unsigned short value)
{
unsigned short result;
__asm__("rlwimi %0,%1,8,16,23"
: "=r" (result)
: "r" (value), "0" (value >> 8));
return result;
}
unsigned short my__arch_swab16(unsigned short value)
{
__asm__("rlwimi %0,%0,16,0x00ff0000"
: "+r" (value));
__asm__("rlwinm %0,%0,24,0x0000ffff"
: "+r"(value));
return value;
}
main()
{
unsigned long x=0x12345678, y;
y = my__arch_swab32(x);
printf("swab32 x:%x, y:%x\n", x, y);
y = my__arch_swab16(x);
printf("swab16 x:%x, y:%x\n", x, y);
}
Generated asm:
.file "tst.c"
.section ".text"
.align 2
.globl __arch_swab32
.type __arch_swab32, @function
__arch_swab32:
mr %r0,%r3
srwi %r3,%r3,24
#APP
rlwimi %r3,%r0,24,16,23
rlwimi %r3,%r0,8,8,15
rlwimi %r3,%r0,24,0,7
#NO_APP
blr
.size __arch_swab32, .-__arch_swab32
.align 2
.globl my__arch_swab32
.type my__arch_swab32, @function
my__arch_swab32:
#APP
rlwimi %r3,%r3,24,0xffffffff
rlwinm %r0,%r3,16,0xffffffff
rlwimi %r3,%r0,0,0x00ff0000
rlwimi %r3,%r0,0,0x000000ff
#NO_APP
blr
.size my__arch_swab32, .-my__arch_swab32
.align 2
.globl __arch_swab16
.type __arch_swab16, @function
__arch_swab16:
mr %r0,%r3
srwi %r3,%r3,8
#APP
rlwimi %r3,%r0,8,16,23
#NO_APP
rlwinm %r3,%r3,0,0xffff
blr
.size __arch_swab16, .-__arch_swab16
.align 2
.globl my__arch_swab16
.type my__arch_swab16, @function
my__arch_swab16:
#APP
rlwimi %r3,%r3,16,0x00ff0000
rlwinm %r3,%r3,24,0x0000ffff
#NO_APP
blr
.size my__arch_swab16, .-my__arch_swab16
.section .rodata.str1.4,"aMS",@progbits,1
.align 2
.LC0:
.string "swab32 x:%x, y:%x\n"
.align 2
.LC1:
.string "swab16 x:%x, y:%x\n"
.section ".text"
.align 2
.globl main
.type main, @function
main:
mflr %r0
lis %r3,0x1234
stwu %r1,-16(%r1)
ori %r3,%r3,22136
stw %r0,20(%r1)
bl my__arch_swab32
mr %r5,%r3
lis %r4,0x1234
lis %r3,.LC0@ha
ori %r4,%r4,22136
la %r3,.LC0@l(%r3)
bl printf
li %r3,22136
bl my__arch_swab16
lis %r4,0x1234
mr %r5,%r3
lis %r3,.LC1@ha
la %r3,.LC1@l(%r3)
ori %r4,%r4,22136
bl printf
lwz %r0,20(%r1)
addi %r1,%r1,16
mtlr %r0
blr
.size main, .-main
.section .note.GNU-stack,"",@progbits
.ident "GCC: (GNU) 3.4.6 (Gentoo 3.4.6-r2, ssp-3.4.6-1.0, pie-8.7.9)"
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