Optimize ValType parsing in wast
#2365
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−152
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Fuzzing timed out recently with a test case and some profiling showed that parsing types was an alarmingly large amount of the profile. This commit optimizes the parsing of `ValType` by avoiding the use of `Lookahead1` for example and the general style of recursive-descent parsing. Recursive descent parsing performs well when there's not a big branch of what to parse next, but in the case of `ValType` there's a lot of possible branches which meant that the prior idioms ended up generating a pretty slow parser. With this commit the fuzz-generated test case parses 3x faster, dropping from ~1s to 300ms. Still not great, but hopefully fast enough for the fuzzer.
pchickey
approved these changes
Oct 27, 2025
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Fuzzing timed out recently with a test case and some profiling showed that parsing types was an alarmingly large amount of the profile. This commit optimizes the parsing of
ValTypeby avoiding the use ofLookahead1for example and the general style of recursive-descent parsing. Recursive descent parsing performs well when there's not a big branch of what to parse next, but in the case ofValTypethere's a lot of possible branches which meant that the prior idioms ended up generating a pretty slow parser.With this commit the fuzz-generated test case parses 3x faster, dropping from ~1s to 300ms. Still not great, but hopefully fast enough for the fuzzer.