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​​Polonius Overview 2019.02.19

​​Relevant links

• ​​Polonius blog posts:

• ​​An alias-based formulation of the borrow checker

• ​​
  

• ​​Polonius and datafrog repositories:

• ​​https://github.com/rust-lang-nursery/polonius

• ​​https://github.com/rust-lang-nursery/datafrog

​​Overview

• ​​Key concepts of Polonius

• ​​Possible rule variants and why they don’t work:

• ​​removing transitive subset rule

• ​​SSA-like renaming variants

• ​​Optimized rules, how they work

• ​​Integration with rustc

​​Context

​​Start with the program:

​​

​​let mut x = 22;

​​let p: &u32 = &x;

​​x += 1;

​​drop(p);

​​

​​Construct the MIR:

​​

​​let vec: Vec<usize>;

​​let tmp0: &mut Vec<usize>;

​​let tmp1: usize;

​​


​​vec.push(22)

​​// desugars to:

​​tmp0 = &mut vec;

​​tmp1 = 22;

​​Vec::push(tmp0, tmp1)

​​

​​Region renumbering:

​​

​​let vec: Vec<usize>;

​​let tmp0: &'a mut Vec<usize>;

​​let tmp1: usize;

​​


​​vec.push(22)

​​// desugars to:

​​tmp0 = &'b mut vec;

​​tmp1 = 22;

​​Vec::push(tmp0, tmp1)

​​

​​Go back to original example:

​​

​​let mut x = 22;