Auto merge of #156053 - cjgillot:optimized-reuse-ctfe, r=<try>

bors · bors · commit fdbcb89c7a51 · 2026-05-01T15:43:31.000Z
Reuse CTFE MIR for constructors.
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
@@ -430,6 +430,7 @@ fn mir_promoted(
     def: LocalDefId,
 ) -> (&Steal<Body<'_>>, &Steal<IndexVec<Promoted, Body<'_>>>) {
     debug_assert!(!tcx.is_trivial_const(def), "Tried to get mir_promoted of a trivial const");
+    debug_assert!(!tcx.is_constructor(def.to_def_id()));
 
     // Ensure that we compute the `mir_const_qualif` for constants at
     // this point, before we steal the mir-const result.
@@ -492,7 +493,6 @@ fn mir_for_ctfe(tcx: TyCtxt<'_>, def_id: LocalDefId) -> &Body<'_> {
 }
 
 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: LocalDefId) -> Body<'_> {
-    // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
     if tcx.is_constructor(def.to_def_id()) {
         // There's no reason to run all of the MIR passes on constructors when
         // we can just output the MIR we want directly. This also saves const
@@ -785,18 +785,18 @@ pub(crate) fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'
 
 /// Optimize the MIR and prepare it for codegen.
 fn optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> &Body<'_> {
-    tcx.arena.alloc(inner_optimized_mir(tcx, did))
-}
-
-fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
     if tcx.is_constructor(did.to_def_id()) {
         // There's no reason to run all of the MIR passes on constructors when
         // we can just output the MIR we want directly. This also saves const
         // qualification and borrow checking the trouble of special casing
         // constructors.
-        return shim::build_adt_ctor(tcx, did.to_def_id());
+        return tcx.mir_for_ctfe(did);
     }
 
+    tcx.arena.alloc(inner_optimized_mir(tcx, did))
+}
+
+fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
     match tcx.hir_body_const_context(did) {
         // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
         // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
