NLL: improve inference with flow results, represent regions with bitsets, and more #46319
Commits on Dec 4, 2017
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separate out the liveness constraints from the final value
It will be useful later for diagnostics to be able to remember where things were live.
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replace constant regions with a post-inference check
Rather than declaring some region variables to be constant, and reporting errors when they would have to change, we instead populate each free region X with a minimal set of points (the CFG plus end(X)), and then we let inference do its thing. This may add other `end(Y)` points into X; we can then check after the fact that indeed `X: Y` holds. This requires a bit of "blame" detection to find where the bad constraint came from: we are currently using a pretty dumb algorithm. Good place for later expansion.
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inform constraint generation using maybe-init
In particular, if we see a variable is DROP-LIVE, but it is not MAYBE-INIT, then we can ignore the drop. This leavess attempt to use more complex refinements of the idea (e.g., for subpaths or subfields) to future work.
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region_infer: BitMatrix representation of region values
This should be more efficient than allocating two BTreeSets for every region variable?—as it is written in rust-lang#45670.
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make
resolve_regions_and_report_errorstake anOutlivesEnvThis revealed some shortcomings, one of which is fixed. Fixes rust-lang#45937.
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extract the code to create
OutlivesBoundsinto its own moduleNow it can be reused by the NLL code.
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constraint_generation: create liveness constraints more thoroughly
We now visit just the stuff in the CFG, and we add liveness constraints for all the random types, regions etc that appear within rvalues and statements.
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move
liberate_late_bound_regionsto a method on the tcxNo reason for it to live on `Inherited`.
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introduce
closure_env_tyhelper to compute ty of closure env argPreviously the code was somewhat duplicated.
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rename "free region" to "universally quantified region"
This has been bugging me. All the regions appear free in the source; the real difference is that some of them are universally quantified (those in the function signature) and some are existentially quantified (those for which we are inferring values).
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