diff options
Diffstat (limited to 'pod')
| -rw-r--r-- | pod/perltodo.pod | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/pod/perltodo.pod b/pod/perltodo.pod index 4f8d77f73b..44638a8ede 100644 --- a/pod/perltodo.pod +++ b/pod/perltodo.pod @@ -624,6 +624,62 @@ bootstrap a cookbook. (List::Util? Class::XSAccessor? Tree::Ternary_XS?) Another option could be deconstructing the implementation of some simpler functions in op.c. +=head2 Allow XSUBs to inline themselves as OPs + +For a simple XSUB, often the subroutine dispatch takes more time than the +XSUB itself. The tokeniser already has the ability to inline constant +subroutines - it would be good to provide a way to inline other subroutines. + +Specifically, simplest approach looks to be to allow an XSUB to provide an +alternative implementation of itself as a custom OP. A new flag bit in +C<CvFLAGS()> would signal to the peephole optimiser to take an optree +such as this: + + b <@> leave[1 ref] vKP/REFC ->(end) + 1 <0> enter ->2 + 2 <;> nextstate(main 1 -e:1) v:{ ->3 + a <2> sassign vKS/2 ->b + 8 <1> entersub[t2] sKS/TARG,1 ->9 + - <1> ex-list sK ->8 + 3 <0> pushmark s ->4 + 4 <$> const(IV 1) sM ->5 + 6 <1> rv2av[t1] lKM/1 ->7 + 5 <$> gv(*a) s ->6 + - <1> ex-rv2cv sK ->- + 7 <$> gv(*x) s/EARLYCV ->8 + - <1> ex-rv2sv sKRM*/1 ->a + 9 <$> gvsv(*b) s ->a + +perform the symbol table lookup of C<rv2cv> and C<gv(*x)>, locate the +pointer to the custom OP that provides the direct implementation, and re- +write the optree something like: + + b <@> leave[1 ref] vKP/REFC ->(end) + 1 <0> enter ->2 + 2 <;> nextstate(main 1 -e:1) v:{ ->3 + a <2> sassign vKS/2 ->b + 7 <1> custom_x -> 8 + - <1> ex-list sK ->7 + 3 <0> pushmark s ->4 + 4 <$> const(IV 1) sM ->5 + 6 <1> rv2av[t1] lKM/1 ->7 + 5 <$> gv(*a) s ->6 + - <1> ex-rv2cv sK ->- + - <$> ex-gv(*x) s/EARLYCV ->7 + - <1> ex-rv2sv sKRM*/1 ->a + 8 <$> gvsv(*b) s ->a + +I<i.e.> the C<gv(*)> OP has been nulled and spliced out of the execution +path, and the C<entersub> OP has been replaced by the custom op. + +This approach should provide a measurable speed up to simple XSUBs inside +tight loops. Initially one would have to write the OP alternative +implementation by hand, but it's likely that this should be reasonably +straightforward for the type of XSUB that would benefit the most. Longer +term, once the run-time implementation is proven, it should be possible to +progressively update ExtUtils::ParseXS to generate OP implementations for +some XSUBs. + =head2 Remove the use of SVs as temporaries in dump.c F<dump.c> contains debugging routines to dump out the contains of perl data |