Auto merge of #85254 - cjgillot:reveal-mir, r=lcnr

Normalize MIR with RevealAll before optimizations.

Fixes #78442

compiler/rustc_mir_transform/src/lib.rs

@@ -66,6 +66,7 @@ mod remove_storage_markers;
 mod remove_unneeded_drops;
 mod remove_zsts;
 mod required_consts;
+mod reveal_all;
 mod separate_const_switch;
 mod shim;
 mod simplify;
@@ -490,6 +491,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     // to them. We run some optimizations before that, because they may be harder to do on the state
     // machine than on MIR with async primitives.
     let optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[
+        &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
         &lower_slice_len::LowerSliceLenCalls, // has to be done before inlining, otherwise actual call will be almost always inlined. Also simple, so can just do first
         &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
         &unreachable_prop::UnreachablePropagation,

compiler/rustc_mir_transform/src/remove_unneeded_drops.rs

@@ -13,7 +13,7 @@ impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
         trace!("Running RemoveUnneededDrops on {:?}", body.source);
 
         let did = body.source.def_id();
-        let param_env = tcx.param_env(did);
+        let param_env = tcx.param_env_reveal_all_normalized(did);
         let mut should_simplify = false;
 
         let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();

compiler/rustc_mir_transform/src/reveal_all.rs

@@ -0,0 +1,58 @@
+//! Normalizes MIR in RevealAll mode.
+
+use crate::MirPass;
+use rustc_middle::mir::visit::*;
+use rustc_middle::mir::*;
+use rustc_middle::ty::{self, Ty, TyCtxt};
+
+pub struct RevealAll;
+
+impl<'tcx> MirPass<'tcx> for RevealAll {
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        // This pass must run before inlining, since we insert callee bodies in RevealAll mode.
+        // Do not apply this transformation to generators.
+        if (tcx.sess.mir_opt_level() >= 3 || !super::inline::is_enabled(tcx))
+            && body.generator.is_none()
+        {
+            let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
+            RevealAllVisitor { tcx, param_env }.visit_body(body);
+        }
+    }
+}
+
+struct RevealAllVisitor<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+}
+
+impl<'tcx> MutVisitor<'tcx> for RevealAllVisitor<'tcx> {
+    #[inline]
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    #[inline]
+    fn visit_ty(&mut self, ty: &mut Ty<'tcx>, _: TyContext) {
+        *ty = self.tcx.normalize_erasing_regions(self.param_env, ty);
+    }
+
+    #[inline]
+    fn process_projection_elem(
+        &mut self,
+        elem: PlaceElem<'tcx>,
+        _: Location,
+    ) -> Option<PlaceElem<'tcx>> {
+        match elem {
+            PlaceElem::Field(field, ty) => {
+                let new_ty = self.tcx.normalize_erasing_regions(self.param_env, ty);
+                if ty != new_ty { Some(PlaceElem::Field(field, new_ty)) } else { None }
+            }
+            // None of those contain a Ty.
+            PlaceElem::Index(..)
+            | PlaceElem::Deref
+            | PlaceElem::ConstantIndex { .. }
+            | PlaceElem::Subslice { .. }
+            | PlaceElem::Downcast(..) => None,
+        }
+    }
+}