Changes between Initial Version and Version 1 of JSCRegExpProcessingAndJSCGoals

Timestamp:

Oct 12, 2018 4:03:43 PM (6 years ago)

Author:

Jon Davis

Comment:

Notes from 2018 WebKit Contributors Meeting

JSCRegExpProcessingAndJSCGoals

@@ +1 @@
+= JavaScriptCore RegExp Processing = 
+''presented by Michael Saboff''
+
+Engine is called: YARR (Yet Another RegExp Runtime)
+
+Has both interpreter and JIT backends
+
+Uses backtracking algorithm (not DFA based)
+
+First thing that happens is that the YARR parses a regex and converts it into a YarrPattern.
+
+Then the YARR interpreter converts the YarrPattern into byte code that it can run.
+
+Question: Why not use a DFA based system? 
+It takes a lot longer to compile a DFA system. Also, because JS regular expressions are irregular you wouldn’t be able to have a DFA based system for that.
+
+Question: How would you know if you wanted to have more tiers of RexExps? 
+We would probably want to see what the areas the extra tier would help us. We would also want to know how often we are going see those cases.
+
+Optimizations that YARR does right now:
+
+Generate different code for different matching purposes. Sometimes the regexp is only used for matching other times they want to access the captured groups.
+
+Check multiple adjacent characters at once (up to 8)
+
+Remove unnecessary enclosing patterns: such as /.*abc.*/ which is the same as /abc/
+
+Character class canonicalization. Such as converting [12345] into (1 <= c && 5 <= c) instead of if (c == 1) return match; else if (c == 2) …
+
+= JSC Goals =
+''presented by Saam Barati''
+
+JetStream 2:
+
+We think that the next thing JSC should optimize is BitInt.
+We also want to improve our memory usage.
+
+New Bytecode format:
+It separates the parts of the Bytecode specific to a particular function from the core instructions. This lets us share the core instructions across processes or save it to disk. Hopefully, it is a win for startup and for non-jit cases.
+
+JetStream 2, which is a new benchmark for JS performance that will be open sourced soon (TM).