Validate CopyForDeref and DerefTemps better and remove them from runtime MIR

[beepster4096]

(split from my WIP #145344)

This PR:

• Removes Rvalue::CopyForDeref and LocalInfo::DerefTemp from runtime MIR
  • Using a new mir pass EraseDerefTemps
  • CopyForDeref(x) is turned into Use(Copy(x))
  • DerefTemp is turned into Boring
    • Not sure if this part is actually necessary, it made more sense in [WIP] Underefer refactoring #145344 with DerefTemp storing actual data that I wanted to keep from having to be kept in sync with the rest of the body in runtime MIR
• Checks in validation that CopyForDeref and DerefTemp are only used together
• Removes special handling for CopyForDeref from many places
• Removes CopyForDeref from custom_mir reverting Custom MIR: Support Rvalue::CopyForDeref #111587
  • In runtime MIR simple copies can be used instead
  • In post cleanup analysis MIR it was already wrong to use due to the lack of support for creating DerefTemp locals
  • Possibly this should be its own PR?
• Adds an argument to deref_finder to avoid creating new DerefTemps and CopyForDeref in runtime MIR.
  • Ideally we would just avoid making intermediate derefs instead of fixing it at the end of a pass / during shim building
• Removes some usages of deref_finder that I found out don't actually do anything

r? oli-obk

[rustbot]

oli-obk is not on the review rotation at the moment.
They may take a while to respond.

[rustbot]

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @davidtwco, @vakaras

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to constck

cc @fee1-dead

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

[WaffleLapkin]

(note that oli is on vacation and will be for quite a while)

[beepster4096]

@rustbot author
r? ghost

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[beepster4096]

r? mir
@rustbot ready

[davidtwco]

It's been long enough since I've looked at a involved MIR change that I'm probably not best suited to this

r? mir

[saethlin]

This mostly touches MIR stuff that I'm less familiar with. @cjgillot and @tmiasko might see something in this that I don't.

I'm reviewing this over the next week or so, just slowly.

[bors]

☔ The latest upstream changes (presumably #146666) made this pull request unmergeable. Please resolve the merge conflicts.

[beepster4096]

I moved erase coroutine shim dereftemps before the test blessing commits in this force push so I didn't have to use --keep-stage 1 to keep std from ICEing. This order makes a bit more sense too

[bors]

☔ The latest upstream changes (presumably #142771) made this pull request unmergeable. Please resolve the merge conflicts.

[saethlin]

I've finally got my head around the diff, and I think this is conceptually simple but annoying to implement.

I know there are currently merge conflicts, but what happens if I

@bors r+ rollup=iffy (conflict-prone)

[bors]

📌 Commit d7824f2 has been approved by saethlin

It is now in the queue for this repository.

[bors]

🔒 Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming self is your fork and upstream is this repository, you can resolve the conflict following these steps:

1. git checkout erasedereftemps (switch to your branch)
2. git fetch upstream master (retrieve the latest master)
3. git rebase upstream/master -p (rebase on top of it)
4. Follow the on-screen instruction to resolve conflicts (check git status if you got lost).
5. git push self erasedereftemps --force-with-lease (update this PR)

You may also read Git Rebasing to Resolve Conflicts by Drew Blessing for a short tutorial.

Please avoid the "Resolve conflicts" button on GitHub. It uses git merge instead of git rebase which makes the PR commit history more difficult to read.

Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how Cargo.lock conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

Auto-merging tests/mir-opt/inline_coroutine_body.run2-{closure#0}.Inline.panic-unwind.diff
Removing tests/mir-opt/building/custom/projections.copy_for_deref.built.after.mir
Auto-merging compiler/rustc_span/src/symbol.rs
Auto-merging compiler/rustc_mir_transform/src/validate.rs
Auto-merging compiler/rustc_mir_transform/src/ref_prop.rs
Auto-merging compiler/rustc_mir_transform/src/jump_threading.rs
Auto-merging compiler/rustc_mir_transform/src/inline.rs
CONFLICT (content): Merge conflict in compiler/rustc_mir_transform/src/inline.rs
Auto-merging compiler/rustc_mir_transform/src/gvn.rs
Auto-merging compiler/rustc_mir_transform/src/dest_prop.rs
Auto-merging compiler/rustc_mir_transform/src/dataflow_const_prop.rs
Auto-merging compiler/rustc_mir_transform/src/coroutine.rs
Auto-merging compiler/rustc_mir_transform/src/copy_prop.rs
Auto-merging compiler/rustc_middle/src/mir/syntax.rs
Auto-merging compiler/rustc_middle/src/mir/mod.rs
Auto-merging compiler/rustc_const_eval/src/check_consts/qualifs.rs
Auto-merging compiler/rustc_codegen_ssa/src/mir/rvalue.rs
Auto-merging compiler/rustc_codegen_cranelift/src/base.rs
Auto-merging compiler/rustc_borrowck/src/lib.rs
Automatic merge failed; fix conflicts and then commit the result.

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rust-log-analyzer]

The job aarch64-gnu-llvm-20-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [mir-opt] tests/mir-opt/dead-store-elimination/ref.rs stdout ----
13   
14       bb0: {
15 -         StorageLive(_2);
- -         _3 = deref_copy (_1.1: &Foo);
+ -         _3 = copy (_1.1: &Foo);
17 -         _2 = &((*_3).2: i32);
18 +         // DBG: _2 = &((*_3).2: i32);
-           _4 = deref_copy (_1.1: &Foo);
+           _4 = copy (_1.1: &Foo);
20           _0 = copy ((*_4).0: i32);
21 -         StorageDead(_2);
22           return;


thread '[mir-opt] tests/mir-opt/dead-store-elimination/ref.rs' panicked at src/tools/compiletest/src/runtest/mir_opt.rs:84:21: