I agree. Many optimizations that can be performed in C or other no runtime eval languages can't be done in Perl since so much context and metadata has to be kept around for a rare eval string or magic to happen. Dereferencing has to be done every time -> or {} appears in code without exception in case its a magic variable. $root{l1}{l2}{l3} really takes 4 dereferences ops every time it is written, and it can be written 7 times in a sub. Very few people (I am one of them) will make a lexical reference to the has slice "\$root{l1}{l2}{l3}" to avoid all the reference ops. I still had a dereference op every time I write "${}" but its better than "load constant on stack, do deref" times 3 opcodes. Sometimes flexibility isn't so flexible. hv_common_key_len could use some refactoring to split out all the magic support into separate function calls to keep it out of the CPU cache. Here are top 18 (actually all functions over 4 KB long) fattest functions in ActivePerl 5.12 (Visual C -O1) in machine code.

_Perl_re_compile        00001021
_Perl_gv_fetchpvn_flags 0000105F
S_scan_const            000010EB
S_regatom               000012FB
S_make_trie             0000148C
_Perl_sv_vcatpvfn       00001620
_Perl_yyparse           000016C2
S_regclass              0000177A
_Perl_do_sv_dump        00001A4D
S_reg                   00001B5F
_perl_clone_using       00001D3C
S_unpack_rec            0000231F
S_study_chunk           00002668
S_pack_rec              00002729
S_find_byclass          00002928
_Perl_keyword           0000359D
S_regmatch              0000438A
_Perl_yylex             00008095
[download]

un/pack I'm surprised it so fat. clone_using could use a couple strategically placed memcpy calls rather than 100s of double/quadword copies.

Use B::Deparse and look at your opcode trees. Reduce number of opcodes and your code is faster. Each ; has overhead (line number switching for not present debugger). Use a comma operator sometimes to reduce nextstates.

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.