refactoring: Kill ref cycle in librustc trans #21024
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r? @eddyb (rust_highfive has picked a reviewer for you, use r? to override) |
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This makes me sad - the old design has served as well. |
Namely, `BlockS` used to carry an `fcx: &'blk FunctionContext`, while the `FunctionContext` carries a reference to the arena that holds the blocks. This creates a chicken/egg problem where we are attempting to assign the lifetime `'blk` to both the `FunctionContext` and to the arena's blocks, which does not work under the new lifetime rules for `Drop`, since there has to be some order in which the two are torn down. To resolve this, I removed the `fcx` from the `BlockS`, and instead turn the `Block` type (which was formerly `&'blk BlockS`) into a struct carrying both the pointer to the `BlockS` as well as the `fcx`.
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@bors: r- (holding off on merging this -- I want to check a few things on my local branch before committing to this refactoring.) |
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@eddyb you'll be happy to know that I just found a couple of changes and/or tricks that make this particular refactoring unnecessary. Closing without merge. |
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This is the first commit from #21022, pulled out into a separate PR to ease future rebasing pain.
This is a semantics-preserving refactoring of the existing code. It removes a cyclic structure from
librustc_trans, so that theBlockSstructures no longer carry a reference to theFunctionContext.