Split rustc_mir

[cjgillot]

Proposal

The current rustc_mir crate contains many different MIR-related analyses and transformations. Some of them are very loosely coupled and can be separated.

This MCP proposes to split rustc_mir into 5 crates:

• rustc_borrowck: MIR-based borrow checker;
• rustc_const_eval: const evaluation framework and queries;
• rustc_mir_dataflow: dataflow analysis framework;
• rustc_mir_transform: optimizations;
• rustc_monomorphize: collection of monomorphizations before codegen.

Dependency graph:

• rustc_mir_dataflow and rustc_monomorphize directly depend on rustc_middle;
• rustc_const_eval depends on rustc_mir_dataflow;
• rustc_borrowck and rustc_mir_transform depend on rustc_const_eval.

Mentors or Reviewers

If you have a reviewer or mentor in mind for this work, mention then
here. You can put your own name here if you are planning to mentor the
work.

PR at rust-lang/rust#80522

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

cc @rust-lang/compiler @rust-lang/compiler-contributors

[oli-obk]

@rustbot second