Do not consider borrowed Freeze locals as SSA.

compiler/rustc_mir_transform/src/copy_prop.rs

@@ -33,9 +33,8 @@ impl<'tcx> MirPass<'tcx> for CopyProp {
 }
 
 fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-    let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
     let borrowed_locals = borrowed_locals(body);
-    let ssa = SsaLocals::new(tcx, param_env, body, &borrowed_locals);
+    let ssa = SsaLocals::new(body);
 
     let fully_moved = fully_moved_locals(&ssa, body);
     debug!(?fully_moved);

compiler/rustc_mir_transform/src/normalize_array_len.rs

@@ -7,7 +7,6 @@ use rustc_index::IndexVec;
 use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, TyCtxt};
-use rustc_mir_dataflow::impls::borrowed_locals;
 
 pub struct NormalizeArrayLen;
 
@@ -24,9 +23,7 @@ impl<'tcx> MirPass<'tcx> for NormalizeArrayLen {
 }
 
 fn normalize_array_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-    let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
-    let borrowed_locals = borrowed_locals(body);
-    let ssa = SsaLocals::new(tcx, param_env, body, &borrowed_locals);
+    let ssa = SsaLocals::new(body);
 
     let slice_lengths = compute_slice_length(tcx, &ssa, body);
     debug!(?slice_lengths);

compiler/rustc_mir_transform/src/ref_prop.rs

@@ -4,7 +4,7 @@ use rustc_index::IndexVec;
 use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
-use rustc_mir_dataflow::impls::{borrowed_locals, MaybeStorageDead};
+use rustc_mir_dataflow::impls::MaybeStorageDead;
 use rustc_mir_dataflow::storage::always_storage_live_locals;
 use rustc_mir_dataflow::Analysis;
 
@@ -82,9 +82,7 @@ impl<'tcx> MirPass<'tcx> for ReferencePropagation {
 }
 
 fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-    let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
-    let borrowed_locals = borrowed_locals(body);
-    let ssa = SsaLocals::new(tcx, param_env, body, &borrowed_locals);
+    let ssa = SsaLocals::new(body);
 
     let mut replacer = compute_replacement(tcx, body, &ssa);
     debug!(?replacer.targets, ?replacer.allowed_replacements, ?replacer.storage_to_remove);

compiler/rustc_mir_transform/src/ssa.rs

@@ -1,11 +1,23 @@
+//! We denote as "SSA" the set of locals that verify the following properties:
+//! 1/ They are only assigned-to once, either as a function parameter, or in an assign statement;
+//! 2/ This single assignment dominates all uses;
+//!
+//! As a consequence of rule 2, we consider that borrowed locals are not SSA, even if they are
+//! `Freeze`, as we do not track that the assignment dominates all uses of the borrow.
+//!
+//! We say a local has a stable address if its address has SSA-like properties:
+//! 1/ It has a single `StorageLive` statement, or none at all (always-live);
+//! 2/ All its uses dominate this `StorageLive` statement.
+//!
+//! We do not discard borrowed locals from this analysis, as we cannot take their address' address.
+
 use either::Either;
 use rustc_data_structures::graph::dominators::Dominators;
 use rustc_index::bit_set::BitSet;
 use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::middle::resolve_bound_vars::Set1;
 use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
-use rustc_middle::ty::{ParamEnv, TyCtxt};
 use rustc_mir_dataflow::storage::always_storage_live_locals;
 
 #[derive(Debug)]
@@ -62,12 +74,7 @@ impl SmallDominators {
 }
 
 impl SsaLocals {
-    pub fn new<'tcx>(
-        tcx: TyCtxt<'tcx>,
-        param_env: ParamEnv<'tcx>,
-        body: &Body<'tcx>,
-        borrowed_locals: &BitSet<Local>,
-    ) -> SsaLocals {
+    pub fn new<'tcx>(body: &Body<'tcx>) -> SsaLocals {
         let assignment_order = Vec::with_capacity(body.local_decls.len());
 
         let assignments = IndexVec::from_elem(Set1::Empty, &body.local_decls);
@@ -80,13 +87,8 @@ impl SsaLocals {
         let mut visitor =
             SsaVisitor { assignments, assignment_order, dominators, direct_uses, storage_live };
 
-        for (local, decl) in body.local_decls.iter_enumerated() {
-            if matches!(body.local_kind(local), LocalKind::Arg) {
-                visitor.assignments[local] = Set1::One(LocationExtended::Arg);
-            }
-            if borrowed_locals.contains(local) && !decl.ty.is_freeze(tcx, param_env) {
-                visitor.assignments[local] = Set1::Many;
-            }
+        for local in body.args_iter() {
+            visitor.assignments[local] = Set1::One(LocationExtended::Arg);
         }
 
         for local in always_storage_live_locals(body).iter() {
@@ -237,6 +239,8 @@ struct SsaVisitor {
 impl<'tcx> Visitor<'tcx> for SsaVisitor {
     fn visit_local(&mut self, local: Local, ctxt: PlaceContext, loc: Location) {
         match ctxt {
+            PlaceContext::MutatingUse(MutatingUseContext::Projection)
+            | PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection) => bug!(),
             PlaceContext::MutatingUse(MutatingUseContext::Store) => {
                 self.assignments[local].insert(LocationExtended::Plain(loc));
                 if let Set1::One(_) = self.assignments[local] {
@@ -246,13 +250,18 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor {
                 self.dominators.check_dominates(&mut self.storage_live[local], loc);
             }
             // Anything can happen with raw pointers, so remove them.
-            PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf)
+            // We do not verify that all uses of the borrow dominate the assignment to `local`,
+            // so we have to remove them too.
+            PlaceContext::NonMutatingUse(
+                NonMutatingUseContext::SharedBorrow
+                | NonMutatingUseContext::ShallowBorrow
+                | NonMutatingUseContext::UniqueBorrow
+                | NonMutatingUseContext::AddressOf,
+            )
             | PlaceContext::MutatingUse(_) => {
                 self.assignments[local] = Set1::Many;
                 self.dominators.check_dominates(&mut self.storage_live[local], loc);
             }
-            // Immutable borrows are taken into account in `SsaLocals::new` by
-            // removing non-freeze locals.
             PlaceContext::NonMutatingUse(_) => {
                 self.dominators.check_dominates(&mut self.assignments[local], loc);
                 self.dominators.check_dominates(&mut self.storage_live[local], loc);
@@ -270,15 +279,17 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor {
             // Do not do anything for storage statements and debuginfo.
             if ctxt.is_use() {
                 // Only change the context if it is a real use, not a "use" in debuginfo.
-                let new_ctxt = PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection);
+                let new_ctxt = PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy);
 
                 self.visit_projection(place.as_ref(), new_ctxt, loc);
                 self.dominators.check_dominates(&mut self.assignments[place.local], loc);
                 self.dominators.check_dominates(&mut self.storage_live[place.local], loc);
             }
             return;
+        } else {
+            self.visit_projection(place.as_ref(), ctxt, loc);
+            self.visit_local(place.local, ctxt, loc);
         }
-        self.super_place(place, ctxt, loc);
     }
 }
 

tests/mir-opt/copy-prop/borrowed_local.f.CopyProp.diff

@@ -20,8 +20,7 @@
       }
 
       bb1: {
--         _0 = opaque::<u8>(_3) -> bb2;    // scope 0 at $DIR/borrowed_local.rs:+12:13: +12:38
-+         _0 = opaque::<u8>(_1) -> bb2;    // scope 0 at $DIR/borrowed_local.rs:+12:13: +12:38
+          _0 = opaque::<u8>(_3) -> bb2;    // scope 0 at $DIR/borrowed_local.rs:+12:13: +12:38
                                            // mir::Constant
                                            // + span: $DIR/borrowed_local.rs:28:28: 28:34
                                            // + literal: Const { ty: fn(u8) -> bool {opaque::<u8>}, val: Value(<ZST>) }

tests/mir-opt/reference_prop.reference_propagation.ReferencePropagation.diff

@@ -178,9 +178,8 @@
           StorageLive(_17);                // scope 9 at $DIR/reference_prop.rs:+22:13: +22:14
           _17 = &_16;                      // scope 9 at $DIR/reference_prop.rs:+22:17: +22:19
           StorageLive(_18);                // scope 10 at $DIR/reference_prop.rs:+23:13: +23:14
--         _18 = (*_16);                    // scope 10 at $DIR/reference_prop.rs:+23:17: +23:19
+          _18 = (*_16);                    // scope 10 at $DIR/reference_prop.rs:+23:17: +23:19
 -         _14 = const ();                  // scope 0 at $DIR/reference_prop.rs:+19:5: +24:6
-+         _18 = _15;                       // scope 10 at $DIR/reference_prop.rs:+23:17: +23:19
           StorageDead(_18);                // scope 10 at $DIR/reference_prop.rs:+24:5: +24:6
           StorageDead(_17);                // scope 9 at $DIR/reference_prop.rs:+24:5: +24:6
           StorageDead(_16);                // scope 8 at $DIR/reference_prop.rs:+24:5: +24:6

tests/mir-opt/reference_prop.reference_propagation_const_ptr.ReferencePropagation.diff

@@ -207,9 +207,8 @@
           StorageLive(_16);                // scope 12 at $DIR/reference_prop.rs:+22:13: +22:14
           _16 = &_15;                      // scope 12 at $DIR/reference_prop.rs:+22:17: +22:19
           StorageLive(_17);                // scope 13 at $DIR/reference_prop.rs:+23:13: +23:14
--         _17 = (*_15);                    // scope 13 at $DIR/reference_prop.rs:+23:17: +23:19
+          _17 = (*_15);                    // scope 13 at $DIR/reference_prop.rs:+23:17: +23:19
 -         _13 = const ();                  // scope 10 at $DIR/reference_prop.rs:+19:5: +24:6
-+         _17 = _14;                       // scope 13 at $DIR/reference_prop.rs:+23:17: +23:19
           StorageDead(_17);                // scope 13 at $DIR/reference_prop.rs:+24:5: +24:6
           StorageDead(_16);                // scope 12 at $DIR/reference_prop.rs:+24:5: +24:6
           StorageDead(_15);                // scope 11 at $DIR/reference_prop.rs:+24:5: +24:6

tests/mir-opt/slice_filter.variant_a-{closure#0}.CopyProp.diff

@@ -101,16 +101,16 @@
       }
 
       bb0: {
--         StorageLive(_3);                 // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
+          StorageLive(_3);                 // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
           _25 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
           _3 = &((*_25).0: usize);         // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
--         StorageLive(_4);                 // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
+          StorageLive(_4);                 // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
           _26 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
           _4 = &((*_26).1: usize);         // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
--         StorageLive(_5);                 // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
+          StorageLive(_5);                 // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
           _27 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
           _5 = &((*_27).2: usize);         // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
--         StorageLive(_6);                 // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
+          StorageLive(_6);                 // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
           _28 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
           _6 = &((*_28).3: usize);         // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
           StorageLive(_7);                 // scope 1 at $DIR/slice_filter.rs:+0:40: +0:56
@@ -184,10 +184,10 @@
       bb3: {
           StorageDead(_16);                // scope 1 at $DIR/slice_filter.rs:+0:75: +0:76
           StorageDead(_7);                 // scope 1 at $DIR/slice_filter.rs:+0:75: +0:76
--         StorageDead(_6);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
--         StorageDead(_5);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
--         StorageDead(_4);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
--         StorageDead(_3);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
+          StorageDead(_6);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
+          StorageDead(_5);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
+          StorageDead(_4);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
+          StorageDead(_3);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
           return;                          // scope 0 at $DIR/slice_filter.rs:+0:76: +0:76
       }
 

tests/mir-opt/slice_filter.variant_a-{closure#0}.DestinationPropagation.diff

@@ -89,15 +89,23 @@
       }
 
       bb0: {
+-         StorageLive(_3);                 // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
++         nop;                             // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
           _25 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
 -         _3 = &((*_25).0: usize);         // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
+-         StorageLive(_4);                 // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
 +         _20 = &((*_25).0: usize);        // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
++         nop;                             // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
           _26 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
 -         _4 = &((*_26).1: usize);         // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
+-         StorageLive(_5);                 // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
 +         _15 = &((*_26).1: usize);        // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
++         nop;                             // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
           _27 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
 -         _5 = &((*_27).2: usize);         // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
+-         StorageLive(_6);                 // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
 +         _11 = &((*_27).2: usize);        // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
++         nop;                             // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
           _28 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
 -         _6 = &((*_28).3: usize);         // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
 -         StorageLive(_7);                 // scope 1 at $DIR/slice_filter.rs:+0:40: +0:56
@@ -162,8 +170,16 @@
       bb3: {
 -         StorageDead(_16);                // scope 1 at $DIR/slice_filter.rs:+0:75: +0:76
 -         StorageDead(_7);                 // scope 1 at $DIR/slice_filter.rs:+0:75: +0:76
+-         StorageDead(_6);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
+-         StorageDead(_5);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
+-         StorageDead(_4);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
+-         StorageDead(_3);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
 +         nop;                             // scope 1 at $DIR/slice_filter.rs:+0:75: +0:76
 +         nop;                             // scope 1 at $DIR/slice_filter.rs:+0:75: +0:76
++         nop;                             // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
++         nop;                             // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
++         nop;                             // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
++         nop;                             // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
           return;                          // scope 0 at $DIR/slice_filter.rs:+0:76: +0:76
       }
 

tests/mir-opt/slice_filter.variant_a-{closure#0}.ReferencePropagation.diff

@@ -93,12 +93,16 @@
       }
 
       bb0: {
+          StorageLive(_3);                 // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
           _25 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
           _3 = &((*_25).0: usize);         // scope 0 at $DIR/slice_filter.rs:+0:27: +0:28
+          StorageLive(_4);                 // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
           _26 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
           _4 = &((*_26).1: usize);         // scope 0 at $DIR/slice_filter.rs:+0:30: +0:31
+          StorageLive(_5);                 // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
           _27 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
           _5 = &((*_27).2: usize);         // scope 0 at $DIR/slice_filter.rs:+0:33: +0:34
+          StorageLive(_6);                 // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
           _28 = deref_copy (*_2);          // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
           _6 = &((*_28).3: usize);         // scope 0 at $DIR/slice_filter.rs:+0:36: +0:37
           StorageLive(_7);                 // scope 1 at $DIR/slice_filter.rs:+0:40: +0:56
@@ -160,6 +164,10 @@
       bb3: {
           StorageDead(_16);                // scope 1 at $DIR/slice_filter.rs:+0:75: +0:76
           StorageDead(_7);                 // scope 1 at $DIR/slice_filter.rs:+0:75: +0:76
+          StorageDead(_6);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
+          StorageDead(_5);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
+          StorageDead(_4);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
+          StorageDead(_3);                 // scope 0 at $DIR/slice_filter.rs:+0:75: +0:76
           return;                          // scope 0 at $DIR/slice_filter.rs:+0:76: +0:76
       }