This perl5 jitter is super-simple, and modeled after B::CC
The compiled perl5 optree is a linked list in memory in non-execution order,
wide-spread jumps. Additionally the calls are indirect. The jitter properly
aligns the run-time calls in linear linked-list "exec" order, so that the CPU
can prefetch the next instructions, and it inlines some simple ops.
op_next targets (returned by false conditions) are favored over op_other and
other targets.
IT DOES NOT WORK YET!
It does only work yet for non-threaded simple functions! No subs, no maybranch ops
Faster jitted execution path without runops loop, selected with -MJit or later,
when stable with perl -j.
All ops are unrolled in execution order for the CPU cache,
prefetching is the main advantage of this function. The perl5 runloop has
no chance to get cached at all.
For < 5.13 the ASYNC check is only done when necessary.
For now only implemented for x86 and amd64/x86_64 with certain
hardcoded my_perl offsets when threaded.
C pseudocode
x86 not-threaded, PL_op in eax, PL_sig_pending temp in ecx
prolog:
55 push %ebp
89 e5 mov %esp,%ebp
53 push %rbx
call:
e8 xx xx xx xx call $PL_op->op_ppaddr #relative
save_plop:
a3 xx xx xx xx mov %eax,$PL_op
dispatch_getsig:
8b 0d xx xx xx xx mov $PL_sig_pending,%ecx
dispatch:
85 c9 test %ecx,%ecx
74 06 je nextcall
e8 xx xx xx xx call *Perl_despatch_signals #relative
epilog:
b8 00 00 00 00 mov $0x0,%eax # clean PL_op
5b pop %rbx
5d pop %ebp
c3 ret
If op maybranch (Opcodes-0.04), create call of other op, check PL_op before with after
and branch to label of other op.
Problems
far calls to the pp ops break code prefetching, so we have to inline as much as
possible, similar to B::CC. Easy to jit are only nextstate, enter, and skip null.
The best jitter would be a B::CC to assembler backend, but this is hard to get right.
Porting
I created the asm with cc_main and cc_main_nt, see Makefile for objdump and cc_harness
rules for gcc assembly.
ASM links
http://www.lxhp.in-berlin.de/lhplinks.html
http://blogs.msdn.com/freik/archive/2005/03/17/398200.aspx
http://msdn.microsoft.com/en-us/library/7kcdt6fy.aspx
http://asm.sourceforge.net//resources.html
http://www.intel.com/design/itanium/manuals/iiasdmanual.htm
http://www.heyrick.co.uk/assembler/qfinder.html
HL jitters
parrot
luajit
psyco / pypy
tracemonkey
ruby
clisp
JIT libs
lightning - c macros only
libjit - c lib
llvm - compiler framework + lib
