On Sun, Apr 10, 2011 at 09:25:33PM +0200, Alexander Graf wrote:
>
> On 10.04.2011, at 21:23, Aurelien Jarno wrote:
>
> > On Tue, Apr 05, 2011 at 09:55:09AM +0200, Alexander Graf wrote:
> >>
> >> On 05.04.2011, at 06:54, Aurelien Jarno wrote:
> >>
> >>> On Mon, Apr 04, 2011 at 04:32:24PM +0200, Alexander Graf wrote:
> >>>> With the s390x target we use the deposit instruction to store 32bit
> >>>> values
> >>>> into 64bit registers without clobbering the upper 32 bits.
> >>>>
> >>>> This specific operation can be optimized slightly by using the ext
> >>>> operation
> >>>> instead of an explicit and in the deposit instruction. This patch adds
> >>>> that
> >>>> special case to the generic deposit implementation.
> >>>>
> >>>> Signed-off-by: Alexander Graf <ag...@suse.de>
> >>>> ---
> >>>> tcg/tcg-op.h | 6 +++++-
> >>>> 1 files changed, 5 insertions(+), 1 deletions(-)
> >>>
> >>> Have you really measuring a difference here? This should already be
> >>> handled, at least on x86, by this code:
> >>>
> >>> if (TCG_TARGET_REG_BITS == 64) {
> >>> if (val == 0xffffffffu) {
> >>> tcg_out_ext32u(s, r0, r0);
> >>> return;
> >>> }
> >>> if (val == (uint32_t)val) {
> >>> /* AND with no high bits set can use a 32-bit operation. */
> >>> rexw = 0;
> >>> }
> >>> }
> >>
> >> I've certainly looked at the -d op logs and seen that instead of creating
> >> a const tcg variable plus an AND there was now an extu opcode issued, yes.
> >> No idea why the case up there didn't trigger.
> >>
> >
> > The question there is looking at -d out_asm. They should be the same at
> > the end as the code I pasted above is from tcg/i386/tcg-target.c.
>
> Yes. I was trying to optimize for maximum op length. TCG defines a maximum
> number of tcg ops to be issued by each target instruction. Since s390 is very
> CISCy, there are instructions that translate into lots of microops, but are
> still faster than a C call (register save/restore mostly).
>
> Without this patch, there are some places where we hit that number :).
Is it on 32-bit on or 64-bit? If we reach this number, it's probably
better to either implement this instruction with an helper, or maybe
increase the number of maximum ops. What is this instruction?
--
Aurelien Jarno GPG: 1024D/F1BCDB73
aurel...@aurel32.net http://www.aurel32.net
