This is more out of curiosity than anything else, as I'm failing to find any useful info on Google about this function (CORE::substcont)
In profiling and optimising some old, slow, XML parsing code I've found that the following regex is calling substcont 31 times for each time the line is executed, and taking a huge amount of time:
Calls: 10000 Time: 2.65s Sub calls: 320000 Time in subs: 1.15s`
$handle =~s/(>)\s*(<)/$1\n$2/g;
# spent 1.09s making 310000 calls to main::CORE:substcont, avg 4µs/call
# spent 58.8ms making 10000 calls to main::CORE:subst, avg 6µs/call
Compared to the immediately preceding line:
Calls: 10000 Time: 371ms Sub calls: 30000 Time in subs: 221ms
$handle =~s/(.*)\s*(<\?)/$1\n$2/g;
# spent 136ms making 10000 calls to main::CORE:subst, avg 14µs/call
# spent 84.6ms making 20000 calls to main::CORE:substcont, avg 4µs/call
The number of substcont calls is quite surprising, especially seeing as I would've thought that the second regex would be more expensive. This is, obviously, why profiling is a Good Thing ;-)
I've subsequently changed both these line to remove the unneccessary backrefs, with dramatic results for the badly-behaving line:
Calls:10000 Time: 393ms Sub calls: 10000 Time in subs: 341ms
$handle =~s/>\s*</>\n</g;
# spent 341ms making 10000 calls to main::CORE:subst, avg 34µs/call
substcont
is Perl's internal name for the "substitution iterator". Something to do with s///
. Based on what little information I have, it seems substcont
is triggered when doing a backref. That is, when $1
is present. You can play with it a bit using B::Concise.
Here's the opcodes of a simple regex without a backref.
$ perl -MO=Concise,-exec -we'$foo = "foo"; $foo =~ s/(foo)/bar/ig'
1 <0> enter
2 <;> nextstate(main 1 -e:1) v:{
3 <$> const[PV "foo"] s
4 <#> gvsv[*foo] s
5 <2> sassign vKS/2
6 <;> nextstate(main 1 -e:1) v:{
7 <#> gvsv[*foo] s
8 <$> const[PV "bar"] s
9 </> subst(/"(foo)"/) vKS
a <@> leave[1 ref] vKP/REFC
-e syntax OK
And one with.
$ perl -MO=Concise,-exec -we'$foo = "foo"; $foo =~ s/(foo)/$1/ig'
1 <0> enter
2 <;> nextstate(main 1 -e:1) v:{
3 <$> const[PV "foo"] s
4 <#> gvsv[*foo] s
5 <2> sassign vKS/2
6 <;> nextstate(main 1 -e:1) v:{
7 <#> gvsv[*foo] s
8 </> subst(/"(foo)"/ replstart->9) vKS
9 <#> gvsv[*1] s
a <|> substcont(other->8) sK/1
b <@> leave[1 ref] vKP/REFC
-e syntax OK
That's all I can offer. You may want to try Rx, mjd's old regex debugger.
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