fix #29036, large slowdown in DelimitedFiles #29075
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In this case, the result of `iterate` has not been checked for
`nothing`, so we try to call `indexed_iterate` (for destructuring
assignment) on a Union of Nothing and the tuple returned by
`iterate`. That has two method matches, and so was excluded from
constant propagation. This commit fixes that by generalizing the
constant prop heuristic from requiring one method match to
requiring one non-Bottom method match.
This issue caused a large slowdown in DelimitedFiles, where
the inner loop consists of
```
while idx <= slen
val,idx = iterate(dbuff, idx)
```
There is no need to fetch the next state after the last element.
JeffBezanson
added
performance
JeffBezanson
changed the title
Keno
approved these changes
Sep 8, 2018
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Fixes #29036.
The cause was poor inference of
val,i = iterate(x,i). From the commit message:In this case, the result of
iteratehas not been checked fornothing, so we try to callindexed_iterate(for destructuring assignment) on a Union of Nothing and the tuple returned byiterate. That has two method matches, and so was excluded from constant propagation. This commit fixes that by generalizing the constant prop heuristic from requiring one method match to requiring one non-Bottom method match.