Have alt-pattern drop the slots it initializes when binding slot patterns. Add a testcase for this as well.

Author: froystig

src/Makefile

@@ -425,6 +425,7 @@ TEST_XFAILS_LLVM := $(TASK_XFAILS) \
                     $(addprefix test/run-pass/, \
                       arith-1.rs \
                       acyclic-unwind.rs \
+                      alt-pattern-drop.rs \
                       alt-pattern-simple.rs \
                       alt-tag.rs \
                       append-units.rs \

src/boot/me/trans.ml

@@ -4138,12 +4138,24 @@ let trans_visitor
 
     let trans_arm arm : quad_idx =
       let (pat, block) = arm.node in
-        (* Translates the pattern and returns the addresses of the branch
-         * instructions, which are taken if the match fails. *)
-      let rec trans_pat pat src_cell src_ty =
+
+      (* Translates the pattern and returns the following pair.
+       *
+       *   fst: The addresses of the branch instructions that are taken if
+       *        the match fails.
+       *   snd: The (cell, slot) pairs of any slots bound and initialized
+       *        in PAT_slot pattern leaves.
+       *)
+      let rec trans_pat
+          (pat:Ast.pat)
+          (src_cell:Il.cell)
+          (src_ty:Ast.ty)
+          : (quad_idx list) * ((Il.cell * Ast.slot) list) =
+
         match pat with
             Ast.PAT_lit lit ->
-              trans_compare_simple Il.JNE (trans_lit lit) (Il.Cell src_cell)
+              (trans_compare_simple Il.JNE (trans_lit lit) (Il.Cell src_cell),
+               [])
 
           | Ast.PAT_tag (lval, pats) ->
               let tag_name = tag_ctor_name_to_tag_name (lval_to_name lval) in
@@ -4173,16 +4185,19 @@ let trans_visitor
 
               let tup_cell:Il.cell = get_variant_ptr union_cell tag_number in
 
-              let trans_elem_pat i elem_pat : quad_idx list =
+              let trans_elem_pat i elem_pat
+                  : (quad_idx list) * ((Il.cell * Ast.slot) list) =
                 let elem_cell =
                   get_element_ptr_dyn_in_current_frame tup_cell i
                 in
                 let elem_ty = ty_tup.(i) in
                   trans_pat elem_pat elem_cell elem_ty
               in
 
-              let elem_jumps = Array.mapi trans_elem_pat pats in
-                next_jumps @ (List.concat (Array.to_list elem_jumps))
+              let (elem_jumps, bindings) =
+                List.split (Array.to_list (Array.mapi trans_elem_pat pats))
+              in
+                (next_jumps @ (List.concat elem_jumps), List.concat bindings)
 
           | Ast.PAT_slot (dst, _) ->
               let dst_slot = get_slot cx dst.id in
@@ -4191,14 +4206,24 @@ let trans_visitor
                   (get_ty_params_of_current_frame())
                   CLONE_none dst_cell dst_slot
                   src_cell src_ty;
-                []                (* irrefutable *)
+                ([], [(dst_cell, dst_slot)])   (* irrefutable *)
 
-          | Ast.PAT_wild -> []    (* irrefutable *)
+          | Ast.PAT_wild -> ([], [])           (* irrefutable *)
       in
 
       let (lval_cell, lval_ty) = trans_lval at.Ast.alt_tag_lval in
-      let next_jumps = trans_pat pat lval_cell lval_ty in
+      let (next_jumps, bindings) = trans_pat pat lval_cell lval_ty in
         trans_block block;
+
+        (* Drop any slots we initialized in the leaf slot bindings of
+         * this arm's pattern.
+         *
+         * FIXME: Is `None` really correct to pass as the curr_iso?
+         *)
+        List.iter
+          (fun (cell, slot) -> drop_slot_in_current_frame cell slot None)
+          bindings;
+
         let last_jump = mark() in
           emit (Il.jmp Il.JMP Il.CodeNone);
           List.iter patch next_jumps;

src/test/run-pass/alt-pattern-drop.rs

@@ -0,0 +1,19 @@
+// -*- rust -*-
+
+use std;
+import std._str;
+
+type t = tag(make_t(str), clam());
+
+fn main() {
+  let str s = "hi";     // ref up
+  let t x = make_t(s);  // ref up
+
+  alt (x) {
+    case (make_t(y)) { log y; }  // ref up and ref down
+    case (_) { log "?"; }
+  }
+
+  log _str.refcount(s);
+  check (_str.refcount(s) == 2u);
+}