Re: [CVS ci] CGP - CGoto Prederefed runloop

[Leopold Toetsch]

Jerome Vouillon wrote:

On Thu, Feb 06, 2003 at 01:37:42PM +0100, Leopold Toetsch wrote:

This is one thing I allways wanted to try ;-)

fast_core MOps: 11
Prederef:       17.5
CGoto MOps:     19.4
CGP MOps:       27.5
CGP -O3 MOps:   65 !!!1

Why not also predereference the operation address?  This would save a
memory read.  The goto would become:

      goto **(cur_opcode += 4);

Many thanks for this hint. I did write "I won't do it" but ehem, yes, here it is:

CGP MOps 34.5
CGP MOps -O3: 92.3

This is now the sub_i_i_i (-O3)

0x80e9060 <cgp_core+9808>: mov 0x4(%esi),%ecx
0x80e9063 <cgp_core+9811>: mov 0x8(%esi),%edx
0x80e9066 <cgp_core+9814>: mov 0xc(%esi),%eax
0x80e9069 <cgp_core+9817>: add $0x10,%esi
0x80e906c <cgp_core+9820>: mov (%eax),%eax
0x80e906e <cgp_core+9822>: mov (%edx),%edx
0x80e9070 <cgp_core+9824>: sub %eax,%edx
0x80e9072 <cgp_core+9826>: mov %edx,(%ecx)
0x80e9074 <cgp_core+9828>: jmp *(%esi)

So this saved 2 instructions including the memory access

This is the branch from mops.pasm
0x80e7ff0 <cgp_core+5600>: mov 0x4(%esi),%eax
0x80e7ff3 <cgp_core+5603>: cmpl $0x0,(%eax)
0x80e7ff6 <cgp_core+5606>: je 0x80e8010 <cgp_core+5632>
0x80e7ff8 <cgp_core+5608>: mov 0x8(%esi),%eax
0x80e7ffb <cgp_core+5611>: mov (%eax),%eax
0x80e7ffd <cgp_core+5613>: shl $0x2,%eax
0x80e8000 <cgp_core+5616>: add %eax,%esi
0x80e8002 <cgp_core+5618>: jmp *(%esi)

leo