Drop arguments on the caller side, not the callee

This makes it easier for the caller to optimize the take/drop away for
temporary values, and opens up new possibilities for alias handling.

Breaks tail calls.

Author: marijnh

src/comp/driver/rustc.rs

@@ -148,26 +148,24 @@ fn compile_input(sess: session::session, cfg: ast::crate_cfg, input: str,
         time(time_passes, "freevar finding",
              bind freevars::annotate_freevars(sess, def_map, crate));
     let ty_cx = ty::mk_ctxt(sess, def_map, ext_map, ast_map, freevars);
-    time::<()>(time_passes, "typechecking",
-               bind typeck::check_crate(ty_cx, crate));
-    time::<()>(time_passes, "alt checking",
-               bind middle::check_alt::check_crate(ty_cx, crate));
+    time(time_passes, "typechecking",
+         bind typeck::check_crate(ty_cx, crate));
+    time(time_passes, "alt checking",
+         bind middle::check_alt::check_crate(ty_cx, crate));
     if sess.get_opts().run_typestate {
         time(time_passes, "typestate checking",
              bind middle::tstate::ck::check_crate(ty_cx, crate));
     }
-    time(time_passes, "alias checking",
-         bind middle::alias::check_crate(ty_cx, crate));
-    time::<()>(time_passes, "kind checking",
-               bind kind::check_crate(ty_cx, crate));
+    let mut_map = time(time_passes, "alias checking",
+                       bind middle::alias::check_crate(ty_cx, crate));
+    time(time_passes, "kind checking",
+         bind kind::check_crate(ty_cx, crate));
     if sess.get_opts().no_trans { ret; }
-    let llmod =
-        time::<llvm::llvm::ModuleRef>(time_passes, "translation",
-                                      bind trans::trans_crate(sess, crate,
-                                                              ty_cx, output,
-                                                              ast_map));
-    time::<()>(time_passes, "LLVM passes",
-               bind link::write::run_passes(sess, llmod, output));
+    let llmod = time(time_passes, "translation",
+                     bind trans::trans_crate(sess, crate, ty_cx, output,
+                                             ast_map, mut_map));
+    time(time_passes, "LLVM passes",
+         bind link::write::run_passes(sess, llmod, output));
 }
 
 fn pretty_print_input(sess: session::session, cfg: ast::crate_cfg, input: str,

src/comp/middle/alias.rs

@@ -36,20 +36,25 @@ type scope = @[restrict];
 
 tag local_info { arg(ast::mode); objfield(ast::mutability); }
 
-type ctx = {tcx: ty::ctxt, local_map: std::map::hashmap<node_id, local_info>};
+type mut_map = std::map::hashmap<node_id, ()>;
+type ctx = {tcx: ty::ctxt,
+            local_map: std::map::hashmap<node_id, local_info>,
+            mut_map: mut_map};
 
-fn check_crate(tcx: ty::ctxt, crate: &@ast::crate) {
+fn check_crate(tcx: ty::ctxt, crate: &@ast::crate) -> mut_map {
     // Stores information about object fields and function
     // arguments that's otherwise not easily available.
-    let cx = @{tcx: tcx, local_map: std::map::new_int_hash()};
-    let v =
-        @{visit_fn: bind visit_fn(cx, _, _, _, _, _, _, _),
-          visit_item: bind visit_item(cx, _, _, _),
-          visit_expr: bind visit_expr(cx, _, _, _),
-          visit_decl: bind visit_decl(cx, _, _, _)
-             with *visit::default_visitor::<scope>()};
+    let cx = @{tcx: tcx,
+               local_map: std::map::new_int_hash(),
+               mut_map: std::map::new_int_hash()};
+    let v = @{visit_fn: bind visit_fn(cx, _, _, _, _, _, _, _),
+              visit_item: bind visit_item(cx, _, _, _),
+              visit_expr: bind visit_expr(cx, _, _, _),
+              visit_decl: bind visit_decl(cx, _, _, _)
+              with *visit::default_visitor::<scope>()};
     visit::visit_crate(*crate, @[], visit::mk_vt(v));
     tcx.sess.abort_if_errors();
+    ret cx.mut_map;
 }
 
 fn visit_fn(cx: &@ctx, f: &ast::_fn, _tp: &[ast::ty_param], _sp: &span,
@@ -425,6 +430,7 @@ fn check_lval(cx: &@ctx, dest: &@ast::expr, sc: &scope, v: &vt<scope>) {
     alt dest.node {
       ast::expr_path(p) {
         let dnum = ast::def_id_of_def(cx.tcx.def_map.get(dest.id)).node;
+        cx.mut_map.insert(dnum, ());
         if is_immutable_alias(*cx, sc, dnum) {
             cx.tcx.sess.span_err(dest.span, "assigning to immutable alias");
         } else if is_immutable_objfield(*cx, dnum) {