Auto merge of #128506 - compiler-errors:by-move-body, r=cjgillot

Stop storing a special inner body for the coroutine by-move body for async closures

...and instead, just synthesize an item which is treated mostly normally by the MIR pipeline.

This PR does a few things:
* We synthesize a new `DefId` for the by-move body of a closure, which has its `mir_built` fed with the output of the `ByMoveBody` MIR transformation, and some other relevant queries.
* This has the `DefKind::ByMoveBody`, which we use to distinguish it from "real" bodies (that come from HIR) which need to be borrowck'd. Introduce `TyCtxt::is_synthetic_mir` to skip over `mir_borrowck` which is called by `mir_promoted`; borrowck isn't really possible to make work ATM since it heavily relies being called on a body generated from HIR, and is redundant by the construction of the by-move-body.
* Remove the special `PassManager` hacks for handling the inner `by_move_body` stored within the coroutine's mir body. Instead, this body is fed like a regular MIR body, so it's goes through all of the `tcx.*_mir` stages normally (build -> promoted -> ...etc... -> optimized) ✨.
* Remove the `InstanceKind::ByMoveBody` shim, since now we have a "regular" def id, we can just use `InstanceKind::Item`. This also allows us to remove the corresponding hacks from codegen, such as in `fn_sig_for_fn_abi` ✨.

Notable remarks:
* ~~I know it's kind of weird to be using `DefKind::Closure` here, since it's not a distinct closure but just a new MIR body. I don't believe it really matters, but I could also use a different `DefKind`... maybe one that we could use for synthetic MIR bodies in general?~~ edit: We're doing this now.

1 files changed, 0 insertions, 19 deletions

diff --git a/compiler/rustc_mir_transform/src/validate.rs b/compiler/rustc_mir_transform/src/validate.rs
index 36908036796..99e06f59dd0 100644
--- a/compiler/rustc_mir_transform/src/validate.rs
+++ b/compiler/rustc_mir_transform/src/validate.rs
@@ -102,25 +102,6 @@ impl<'tcx> MirPass<'tcx> for Validator {
                 }
             }
         }
-
-        // Enforce that coroutine-closure layouts are identical.
-        if let Some(layout) = body.coroutine_layout_raw()
-            && let Some(by_move_body) = body.coroutine_by_move_body()
-            && let Some(by_move_layout) = by_move_body.coroutine_layout_raw()
-        {
-            // FIXME(async_closures): We could do other validation here?
-            if layout.variant_fields.len() != by_move_layout.variant_fields.len() {
-                cfg_checker.fail(
-                    Location::START,
-                    format!(
-                        "Coroutine layout has different number of variant fields from \
-                        by-move coroutine layout:\n\
-                        layout: {layout:#?}\n\
-                        by_move_layout: {by_move_layout:#?}",
-                    ),
-                );
-            }
-        }
     }
 }