Another liveness hack#63
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lthls merged 7 commits intoocaml-flambda:flambda2.0-stablefrom Apr 6, 2020
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Preliminary results seem to indicate that liveness works fine, but something else allocates a lot and I couldn't get past the OOM killer. I will look further. |
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So apparently, |
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Merging for now, as it blocks further testing, but this should still be reviewed |
mshinwell
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* Avoid exponential case in liveness * Avoid quadratic cases for free conts * Remove mutable state from spill * Remove leftover debug * Use cache for reload * Remove useless reference in spill * Add cache for spill Co-authored-by: Pierre Chambart <pierre.chambart@ocamlpro.com>
lthls
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* Avoid exponential case in liveness * Avoid quadratic cases for free conts * Remove mutable state from spill * Remove leftover debug * Use cache for reload * Remove useless reference in spill * Add cache for spill Co-authored-by: Pierre Chambart <pierre.chambart@ocamlpro.com>
poechsel
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This tries to avoid exponential blow-up in liveness.
The initial idea from @chambart was to notice if we're recomputing the live set of an expression with the same arguments, in which case we can reuse the previous result.
However, there was a bug because the previous result was read from the
livefield of the next instruction, which can contain an initial empty set or the result of a previous run, but doesn't mean it is actually the result of the analysis.In addition, the
envparameter needs to be compared too, and it is not stored anywhere.So I introduced a cache that remembers, for each handler, the last arguments (
envandat_join) and result (before_handler) of the last time we went through it.Of course, this doesn't help much, because the environment will likely be different each time (otherwise we wouldn't get called again), so I cached the restriction of the environment to the free continuations of the handler, which should be safe and still avoid the exponential blow-up.
I haven't run the libbigarray test yet, but will try it and report if it compiles in a reasonable amount of time.