Do not check copiability.

compiler/rustc_mir_transform/src/gvn.rs

@@ -80,7 +80,6 @@ fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let mut any_replacement = false;
     let mut replacer = Replacer {
         tcx,
-        param_env,
         ssa,
         dominators,
         state,
@@ -213,8 +212,14 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
     #[instrument(level = "trace", skip(self))]
     fn assign(&mut self, local: Local, value: VnIndex) {
         self.locals[local] = Some(value);
+
+        // Only register the value if its type is `Sized`, as we will emit copies of it.
+        let is_sized = !self.tcx.features().unsized_locals
+            || self.local_decls[local].ty.is_sized(self.tcx, self.param_env);
+        if is_sized {
             self.rev_locals.entry(value).or_default().push(local);
         }
+    }
 
     /// Represent the *value* which would be read from `place`.
     #[instrument(level = "trace", skip(self), ret)]
@@ -341,7 +346,6 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
 
 struct Replacer<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
     ssa: SsaLocals,
     dominators: Dominators<BasicBlock>,
     state: VnState<'a, 'tcx>,
@@ -370,13 +374,6 @@ impl<'tcx> Replacer<'_, 'tcx> {
             .copied()
             .find(|&other| self.ssa.assignment_dominates(&self.dominators, other, loc))
     }
-
-    fn is_local_copiable(&self, local: Local) -> bool {
-        let ty = self.state.local_decls[local].ty;
-        // We only unify copy types as we only emit copies.
-        // We already simplify mutable reborrows as assignments, so we also allow copying those.
-        ty.is_ref() || ty.is_copy_modulo_regions(self.tcx, self.param_env)
-    }
 }
 
 impl<'tcx> MutVisitor<'tcx> for Replacer<'_, 'tcx> {
@@ -393,7 +390,6 @@ impl<'tcx> MutVisitor<'tcx> for Replacer<'_, 'tcx> {
                 *self.any_replacement = true;
             } else if let Some(local) = self.try_as_local(value, location)
                 && *operand != Operand::Move(local.into())
-                && self.is_local_copiable(local)
             {
                 *operand = Operand::Copy(local.into());
                 self.reused_locals.insert(local);
@@ -412,7 +408,6 @@ impl<'tcx> MutVisitor<'tcx> for Replacer<'_, 'tcx> {
                 *self.any_replacement = true;
             } else if let Some(local) = self.try_as_local(value, location)
                 && *rvalue != Rvalue::Use(Operand::Move(local.into()))
-                && self.is_local_copiable(local)
             {
                 *rvalue = Rvalue::Use(Operand::Copy(local.into()));
                 self.reused_locals.insert(local);

tests/mir-opt/gvn.rs

@@ -34,8 +34,8 @@ fn subexpression_elimination(x: u64, y: u64, mut z: u64) {
     opaque((x ^ y) + z);
     opaque((x << y) + z);
     opaque((x >> y) + z);
-    opaque(S(x)); //< This is not substituted as `S` is not `Copy`.
+    opaque(S(x));
-    opaque(S(x).0); //<  But this can be.
+    opaque(S(x).0);
 
     // We can substitute through an immutable reference too.
     let a = &z;

tests/mir-opt/gvn.subexpression_elimination.GVN.panic-abort.diff

@@ -405,17 +405,18 @@
           StorageDead(_50);
           StorageDead(_49);
           StorageLive(_52);
-          StorageLive(_53);
+-         StorageLive(_53);
 -         StorageLive(_54);
 -         _54 = _1;
 -         _53 = S::<u64>(move _54);
 -         StorageDead(_54);
+-         _52 = opaque::<S<u64>>(move _53) -> [return: bb15, unwind unreachable];
 +         _53 = S::<u64>(_1);
-          _52 = opaque::<S<u64>>(move _53) -> [return: bb15, unwind unreachable];
++         _52 = opaque::<S<u64>>(_53) -> [return: bb15, unwind unreachable];
       }
   
       bb15: {
-          StorageDead(_53);
+-         StorageDead(_53);
           StorageDead(_52);
           StorageLive(_55);
 -         StorageLive(_56);
@@ -424,7 +425,7 @@
 -         _58 = _1;
 -         _57 = S::<u64>(move _58);
 -         StorageDead(_58);
-+         _57 = S::<u64>(_1);
++         _57 = _53;
           _56 = (_57.0: u64);
 -         _55 = opaque::<u64>(move _56) -> [return: bb16, unwind unreachable];
 +         _55 = opaque::<u64>(_56) -> [return: bb16, unwind unreachable];
@@ -667,17 +668,17 @@
           StorageDead(_116);
           StorageDead(_115);
           StorageLive(_121);
-          StorageLive(_122);
+-         StorageLive(_122);
 -         StorageLive(_123);
 -         _123 = _1;
 -         _122 = S::<u64>(move _123);
 -         StorageDead(_123);
-+         _122 = S::<u64>(_1);
+-         _121 = opaque::<S<u64>>(move _122) -> [return: bb29, unwind unreachable];
-          _121 = opaque::<S<u64>>(move _122) -> [return: bb29, unwind unreachable];
++         _121 = opaque::<S<u64>>(_53) -> [return: bb29, unwind unreachable];
       }
   
       bb29: {
-          StorageDead(_122);
+-         StorageDead(_122);
           StorageDead(_121);
           StorageLive(_124);
 -         StorageLive(_125);

tests/mir-opt/gvn.subexpression_elimination.GVN.panic-unwind.diff

@@ -405,17 +405,18 @@
           StorageDead(_50);
           StorageDead(_49);
           StorageLive(_52);
-          StorageLive(_53);
+-         StorageLive(_53);
 -         StorageLive(_54);
 -         _54 = _1;
 -         _53 = S::<u64>(move _54);
 -         StorageDead(_54);
+-         _52 = opaque::<S<u64>>(move _53) -> [return: bb15, unwind continue];
 +         _53 = S::<u64>(_1);
-          _52 = opaque::<S<u64>>(move _53) -> [return: bb15, unwind continue];
++         _52 = opaque::<S<u64>>(_53) -> [return: bb15, unwind continue];
       }
   
       bb15: {
-          StorageDead(_53);
+-         StorageDead(_53);
           StorageDead(_52);
           StorageLive(_55);
 -         StorageLive(_56);
@@ -424,7 +425,7 @@
 -         _58 = _1;
 -         _57 = S::<u64>(move _58);
 -         StorageDead(_58);
-+         _57 = S::<u64>(_1);
++         _57 = _53;
           _56 = (_57.0: u64);
 -         _55 = opaque::<u64>(move _56) -> [return: bb16, unwind continue];
 +         _55 = opaque::<u64>(_56) -> [return: bb16, unwind continue];
@@ -667,17 +668,17 @@
           StorageDead(_116);
           StorageDead(_115);
           StorageLive(_121);
-          StorageLive(_122);
+-         StorageLive(_122);
 -         StorageLive(_123);
 -         _123 = _1;
 -         _122 = S::<u64>(move _123);
 -         StorageDead(_123);
-+         _122 = S::<u64>(_1);
+-         _121 = opaque::<S<u64>>(move _122) -> [return: bb29, unwind continue];
-          _121 = opaque::<S<u64>>(move _122) -> [return: bb29, unwind continue];
++         _121 = opaque::<S<u64>>(_53) -> [return: bb29, unwind continue];
       }
   
       bb29: {
-          StorageDead(_122);
+-         StorageDead(_122);
           StorageDead(_121);
           StorageLive(_124);
 -         StorageLive(_125);