Auto merge of #99946 - tmiasko:elide-storage-makers, r=oli-obk

Elide superfluous storage markers

Follow the existing strategy of omitting the storage markers for temporaries
introduced for internal usage when elaborating derefs and deref projections.

Those temporaries are simple scalars which are used immediately after being
defined and never have their address taken. There is no benefit from storage
markers from either liveness analysis or code generation perspective.

3 files changed, 8 insertions, 29 deletions

diff --git a/compiler/rustc_mir_transform/src/deref_separator.rs b/compiler/rustc_mir_transform/src/deref_separator.rs
index 87d7b664015..8869f3f92af 100644
--- a/compiler/rustc_mir_transform/src/deref_separator.rs
+++ b/compiler/rustc_mir_transform/src/deref_separator.rs
@@ -28,8 +28,6 @@ impl<'tcx> MutVisitor<'tcx> for DerefChecker<'tcx> {
             let mut last_len = 0;
             let mut last_deref_idx = 0;
 
-            let mut prev_temp: Option<Local> = None;
-
             for (idx, elem) in place.projection[0..].iter().enumerate() {
                 if *elem == ProjectionElem::Deref {
                     last_deref_idx = idx;
@@ -39,14 +37,12 @@ impl<'tcx> MutVisitor<'tcx> for DerefChecker<'tcx> {
             for (idx, (p_ref, p_elem)) in place.iter_projections().enumerate() {
                 if !p_ref.projection.is_empty() && p_elem == ProjectionElem::Deref {
                     let ty = p_ref.ty(&self.local_decls, self.tcx).ty;
-                    let temp = self.patcher.new_local_with_info(
+                    let temp = self.patcher.new_internal_with_info(
                         ty,
                         self.local_decls[p_ref.local].source_info.span,
                         Some(Box::new(LocalInfo::DerefTemp)),
                     );
 
-                    self.patcher.add_statement(loc, StatementKind::StorageLive(temp));
-
                     // We are adding current p_ref's projections to our
                     // temp value, excluding projections we already covered.
                     let deref_place = Place::from(place_local)
@@ -66,22 +62,8 @@ impl<'tcx> MutVisitor<'tcx> for DerefChecker<'tcx> {
                             Place::from(temp).project_deeper(&place.projection[idx..], self.tcx);
                         *place = temp_place;
                     }
-
-                    // We are destroying the previous temp since it's no longer used.
-                    if let Some(prev_temp) = prev_temp {
-                        self.patcher.add_statement(loc, StatementKind::StorageDead(prev_temp));
-                    }
-
-                    prev_temp = Some(temp);
                 }
             }
-
-            // Since we won't be able to reach final temp, we destroy it outside the loop.
-            if let Some(prev_temp) = prev_temp {
-                let last_loc =
-                    Location { block: loc.block, statement_index: loc.statement_index + 1 };
-                self.patcher.add_statement(last_loc, StatementKind::StorageDead(prev_temp));
-            }
         }
     }
 }
diff --git a/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs b/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
index 76522233689..e04094153df 100644
--- a/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
+++ b/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
@@ -69,9 +69,7 @@ impl<'tcx, 'a> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'tcx, 'a> {
             let (unique_ty, nonnull_ty, ptr_ty) =
                 build_ptr_tys(tcx, base_ty.boxed_ty(), self.unique_did, self.nonnull_did);
 
-            let ptr_local = self.patch.new_temp(ptr_ty, source_info.span);
-
-            self.patch.add_statement(location, StatementKind::StorageLive(ptr_local));
+            let ptr_local = self.patch.new_internal(ptr_ty, source_info.span);
 
             self.patch.add_assign(
                 location,
@@ -83,11 +81,6 @@ impl<'tcx, 'a> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'tcx, 'a> {
             );
 
             place.local = ptr_local;
-
-            self.patch.add_statement(
-                Location { block: location.block, statement_index: location.statement_index + 1 },
-                StatementKind::StorageDead(ptr_local),
-            );
         }
 
         self.super_place(place, context, location);
diff --git a/compiler/rustc_mir_transform/src/inline.rs b/compiler/rustc_mir_transform/src/inline.rs
index 6704d3462f4..c478c17be76 100644
--- a/compiler/rustc_mir_transform/src/inline.rs
+++ b/compiler/rustc_mir_transform/src/inline.rs
@@ -616,7 +616,9 @@ impl<'tcx> Inliner<'tcx> {
                 // If there are any locals without storage markers, give them storage only for the
                 // duration of the call.
                 for local in callee_body.vars_and_temps_iter() {
-                    if integrator.always_live_locals.contains(local) {
+                    if !callee_body.local_decls[local].internal
+                        && integrator.always_live_locals.contains(local)
+                    {
                         let new_local = integrator.map_local(local);
                         caller_body[callsite.block].statements.push(Statement {
                             source_info: callsite.source_info,
@@ -629,7 +631,9 @@ impl<'tcx> Inliner<'tcx> {
                     // the slice once.
                     let mut n = 0;
                     for local in callee_body.vars_and_temps_iter().rev() {
-                        if integrator.always_live_locals.contains(local) {
+                        if !callee_body.local_decls[local].internal
+                            && integrator.always_live_locals.contains(local)
+                        {
                             let new_local = integrator.map_local(local);
                             caller_body[block].statements.push(Statement {
                                 source_info: callsite.source_info,