Re: [Qemu-devel] [PATCH 2/2] tcg-ppc: use new return-argument ld/st helpers

[Richard Henderson <rth@twiddle.net>]

On 09/05/2013 01:22 AM, Paolo Bonzini wrote:
> These use a 32-bit load-of-immediate to save a mflr+addi+mtlr sequence.
> Tested with a Windows 98 guest (pretty much the most recent thing I
> could run on my PPC machine) and kvm-unit-tests's sieve.flat.  The
> speed up for sieve.flat is as high as 10% for qemu-system-i386, 25%
> (no kidding) for qemu-system-x86_64 on my PowerBook G4.

See also the series beginning at

http://lists.nongnu.org/archive/html/qemu-devel/2013-09/msg00025.html

The major difference is that I use a conditional call out of the fast
path, which lets me later just use one mflr to pass the parameter.  I
also, perhaps foolishly, got rid of the trampolines.  E.g.

0xf57a1838:  rlwinm  r3,r15,24,20,27
0xf57a183c:  rlwinm  r0,r15,0,30,19
0xf57a1840:  add     r3,r3,r27
0xf57a1844:  lwz     r4,6436(r3)
0xf57a1848:  cmpw    cr7,r0,r4
0xf57a184c:  lwz     r3,6444(r3)
0xf57a1850:  bnel-   cr7,0xf57a1910
0xf57a1854:  stwx    r16,r3,r15
...
0xf57a1910:  mr      r3,r27
0xf57a1914:  mr      r4,r15
0xf57a1918:  mr      r5,r16
0xf57a191c:  li      r6,1
0xf57a1920:  mflr    r7
0xf57a1924:  lis     r0,4120
0xf57a1928:  ori     r0,r0,45040
0xf57a192c:  mtctr   r0
0xf57a1930:  bctrl
0xf57a1934:  b       0xf57a1858


I don't see anything technically wrong with your patch.  But I'd be
interested to compare vs mine.


r~