Remove the mir_build hook.

It was downgraded from a query in rust-lang#122721 but it can just be a vanilla
function because it's not called in `rustc_middle`.

Author: nnethercote

compiler/rustc_middle/src/hooks/mod.rs

@@ -75,12 +75,6 @@ declare_hooks! {
     /// (Eligible functions might nevertheless be skipped for other reasons.)
     hook is_eligible_for_coverage(key: LocalDefId) -> bool;
 
-    /// Create the MIR for a given `DefId` - this includes
-    /// unreachable code.
-    /// You do not want to call this yourself, instead use the cached version
-    /// via `mir_built`
-    hook build_mir(key: LocalDefId) -> mir::Body<'tcx>;
-
     /// Imports all `SourceFile`s from the given crate into the current session.
     /// This normally happens automatically when we decode a `Span` from
     /// that crate's metadata - however, the incr comp cache needs

compiler/rustc_mir_build/src/builder/custom/mod.rs

@@ -6,7 +6,7 @@
 //! present, and if so we branch off into this module, which implements the attribute by
 //! implementing a custom lowering from THIR to MIR.
 //!
-//! The result of this lowering is returned "normally" from the `build_mir` hook, with the only
+//! The result of this lowering is returned "normally" from `build_mir`, with the only
 //! notable difference being that the `injected` field in the body is set. Various components of the
 //! MIR pipeline, like borrowck and the pass manager will then consult this field (via
 //! `body.should_skip()`) to skip the parts of the MIR pipeline that precede the MIR phase the user

compiler/rustc_mir_build/src/builder/mod.rs

@@ -20,7 +20,6 @@ use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_middle::hir::place::PlaceBase as HirPlaceBase;
 use rustc_middle::middle::region;
 use rustc_middle::mir::*;
-use rustc_middle::query::TyCtxtAt;
 use rustc_middle::thir::{self, ExprId, LintLevel, LocalVarId, Param, ParamId, PatKind, Thir};
 use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt, TypeVisitableExt, TypingMode};
 use rustc_middle::{bug, span_bug};
@@ -45,9 +44,9 @@ pub(crate) fn closure_saved_names_of_captured_variables<'tcx>(
         .collect()
 }
 
-/// Construct the MIR for a given `DefId`.
-pub(crate) fn build_mir<'tcx>(tcx: TyCtxtAt<'tcx>, def: LocalDefId) -> Body<'tcx> {
-    let tcx = tcx.tcx;
+/// Create the MIR for a given `DefId`, including unreachable code. Do not call
+/// this directly; instead use the cached version via `mir_built`.
+pub fn build_mir<'tcx>(tcx: TyCtxt<'tcx>, def: LocalDefId) -> Body<'tcx> {
     tcx.ensure_with_value().thir_abstract_const(def);
     if let Err(e) = tcx.check_match(def) {
         return construct_error(tcx, def, e);

compiler/rustc_mir_build/src/lib.rs

@@ -14,7 +14,7 @@
 // The `builder` module used to be named `build`, but that was causing GitHub's
 // "Go to file" feature to silently ignore all files in the module, probably
 // because it assumes that "build" is a build-output directory. See #134365.
-mod builder;
+pub mod builder;
 mod check_tail_calls;
 mod check_unsafety;
 mod errors;
@@ -27,7 +27,6 @@ rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
 pub fn provide(providers: &mut Providers) {
     providers.check_match = thir::pattern::check_match;
     providers.lit_to_const = thir::constant::lit_to_const;
-    providers.hooks.build_mir = builder::build_mir;
     providers.closure_saved_names_of_captured_variables =
         builder::closure_saved_names_of_captured_variables;
     providers.check_unsafety = check_unsafety::check_unsafety;

compiler/rustc_mir_transform/src/lib.rs

@@ -33,6 +33,7 @@ use rustc_middle::mir::{
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
 use rustc_middle::util::Providers;
 use rustc_middle::{bug, query, span_bug};
+use rustc_mir_build::builder::build_mir;
 use rustc_span::source_map::Spanned;
 use rustc_span::{DUMMY_SP, sym};
 use tracing::debug;
@@ -368,7 +369,7 @@ fn mir_const_qualif(tcx: TyCtxt<'_>, def: LocalDefId) -> ConstQualifs {
 }
 
 fn mir_built(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal<Body<'_>> {
-    let mut body = tcx.build_mir(def);
+    let mut body = build_mir(tcx, def);
 
     pass_manager::dump_mir_for_phase_change(tcx, &body);