Avoid boxing arrays (#230 rebased) #375
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Let's make sure this works decently with recent GHC. Some things have gotten harder. Sigh |
sjakobi
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Mar 12, 2022
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| #if MIN_VERSION_base(4,9,0) | ||
| -- GHC can't unbox across the runRW# boundary, so we apply the Array constructor | ||
| -- on the outside. | ||
| run (ST act) = | ||
| case runRW# $ \s -> | ||
| case act s of { (# s', MArray mary #) -> | ||
| unsafeFreezeSmallArray# mary s' } of | ||
| (# _, ary #) -> Array ary | ||
| #else | ||
| run act = runST (act >>= unsafeFreeze) | ||
| #endif |
I like what I've seen so far in the Core. The only inner I probably won't bother to look at Core diffs across GHC versions, so if you're suspecting that some things that this patch used to do don't work anymore with recent GHCs, you'll have to figure this out yourself. |
Previously, we used a lot of things that looked like
runST (act >>= unsafeFreeze)
The trouble is that GHC can't unbox past the `runRW#` primitive
that `runST` is based on. So this actually allocates an `Array`
constructor which we will then throw away immediately.
The way to avoid this is to call `runRW#` manually to produce
a raw `SmallArray#`, then apply the `Array` constructor on the
outside.
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Previously, we used a lot of things that looked like
The trouble is that GHC can't unbox past the
runRW#primitivethat
runSTis based on. So this actually allocates anArrayconstructor which we will then throw away immediately.
The way to avoid this is to call
runRW#manually to producea raw
SmallArray#, then apply theArrayconstructor on theoutside.