> I have not yet been able to build an environment to run the testsuite
> with qemu-ppc (not sure about the best target & dejagnu board
> selection).
No problem, that wasn't really a requirement.
> However, when compiling a sample test
> short myswaps16(short x) {
> return (x << 8) | (x >> 8);
> }
> unsigned short myswapu16(unsigned short x) {
> return (x << 8) | (x >> 8);
> }
>
> The generated code is now:
> myswaps16:
> rlwinm 10,3,8,16,23
> rlwinm 9,3,24,24,31
> or 9,9,10
> extsh 3,9
> blr
>
> myswapu16:
> rlwinm 10,3,8,16,23
> rlwinm 9,3,24,24,31
> or 9,9,10
> rlwinm 3,9,0,0xffff
> blr
>
> While it was (without my patch):
>
> myswaps16:
> slwi 9,3,8
> srawi 3,3,8
> or 3,9,3
> extsh 3,3
> blr
>
> myswapu16:
> srwi 9,3,8
> rlwinm 3,3,8,16,23
> or 3,3,9
> blr
>
> I don't know PowerPC, but I am not sure it's an improvement. Is it?
That indeed doesn't look obvious, especially in the unsigned case. The
PowerPC back-end has a splitter for bswap:HI which generates no less than 3
instructions, so I presume we're seeing its effects here.
I've CCed the other interested parties. David, Michael, Segher, any comments
about or insights into the results reported by Christophe for PowerPC?
--
Eric Botcazou
