Auto merge of rust-lang#145477 - cjgillot:codegen-mode, r=oli-obk

Introduce `TypingMode::Codegen` to avoid layout cycles on coroutines



Computing layout of coroutines depends on their `optimized_mir`. At the same time, MIR opts can require using layouts to work. For instance to evaluate constants. This leads to cycles and clumsy workarounds.

This PR creates a new typing mode for layout computations:
- when a coroutine's layout is requested with `TypingMode::PostAnalysis` or earlier, return `LayourError::TooGeneric`;
- when a coroutine's layout is requested with `TypingMode::Codegen`, actually compute it.

`TypingMode::Codegen` is meant be be used by codegen code, and analyses that require coroutine layout, like transmute check and coroutine recursion check.

With this PR, we can remove all `is_coroutine` checks from `rustc_mir_transform` and unlock simplifying coroutine MIR.

Perf is not terrific. This PR causes recomputation of a few queries, and I had to insert workarounds.

Author: bors

clippy_lints/src/large_futures.rs

@@ -64,7 +64,7 @@ impl<'tcx> LateLintPass<'tcx> for LargeFuture {
             && let ty = cx.typeck_results().expr_ty(arg)
             && let Some(future_trait_def_id) = cx.tcx.lang_items().future_trait()
             && implements_trait(cx, ty, future_trait_def_id, &[])
-            && let Ok(layout) = cx.tcx.layout_of(cx.typing_env().as_query_input(ty))
+            && let Ok(layout) = cx.tcx.layout_of(cx.typing_env().with_codegen_normalized(cx.tcx).as_query_input(ty))
             && let size = layout.layout.size()
             && size >= Size::from_bytes(self.future_size_threshold)
         {