compiler: Fix type inference bug for bit strings #7271
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CT Test Results 2 files 296 suites 13m 21s ⏱️ Results for commit fd735d6. ♻️ This comment has been updated with latest results. To speed up review, make sure that you have read Contributing to Erlang/OTP and that all checks pass. See the TESTING and DEVELOPMENT HowTo guides for details about how to run test locally. Artifacts// Erlang/OTP Github Action Bot |
bjorng
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May 23, 2023
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We want to include this PR in an emergency patch release. Please rebase your branch like this and force-push: |
The beam_ssa_type pass deduces the type of variables from the result of relational operators. In the true-branch following a `A '=:=' B`, the variables `A` and `B` are deduced to be of the type `beam_types:meet(type(A), type(B))` which is not necessarily true for bit strings. Bit strings are special in that nothing about their appendable-status can be deduced from a comparison. The only information gained is the size_unit. The appendable status is unchanged by the comparison. This patch corrects a type inference bug for bit strings where a comparison would falsely set the appendable flag for non-appendable bit strings in the true-branch. The fix special-cases the type inferring following a `=:=` when one or both arguments are appendable by clearing the appendable status, calculating the resulting type and then restoring the appendable-status of the variables.
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The beam_ssa_type pass deduces the type of variables from the result of relational operators. In the true-branch following a
A '=:=' B, the variablesAandBare deduced to be of the typebeam_types:meet(type(A), type(B))which is not necessarily true for bit strings. Bit strings are special in that nothing about their appendable-status can be deduced from a comparison. The only information gained is the size_unit. The appendable status is unchanged by the comparison.This patch corrects a type inference bug for bit strings where a comparison would falsely set the appendable flag for non-appendable bit strings in the true-branch. The fix special-cases the type inferring following a
=:=when one or both arguments are appendable by clearing the appendable status, calculating the resulting type and then restoring the appendable-status of the variables.[edited to match updated commit message]