rustc: reuse const vals, translate fn paths as consts. Close #2530.

Author: graydon

src/libcore/condition.rs

@@ -96,18 +96,16 @@ struct Guard<T, U:Copy> {
 mod test {
 
     fn sadness_key(_x: @Handler<int,int>) { }
+    const sadness_condition : Condition<int,int> =
+        Condition { key: sadness_key };
+
     fn trouble(i: int) {
-        // Condition should work as a const, just limitations in consts.
-        let sadness_condition : Condition<int,int> =
-            Condition { key: sadness_key };
         debug!("trouble: raising conition");
         let j = sadness_condition.raise(&i);
         debug!("trouble: handler recovered with %d", j);
     }
 
     fn nested_trap_test_inner() {
-        let sadness_condition : Condition<int,int> =
-            Condition { key: sadness_key };
 
         let mut inner_trapped = false;
 
@@ -126,9 +124,6 @@ mod test {
     #[test]
     fn nested_trap_test_outer() {
 
-        let sadness_condition : Condition<int,int> =
-            Condition { key: sadness_key };
-
         let mut outer_trapped = false;
 
         do sadness_condition.trap(|_j| {
@@ -144,8 +139,6 @@ mod test {
     }
 
     fn nested_reraise_trap_test_inner() {
-        let sadness_condition : Condition<int,int> =
-            Condition { key: sadness_key };
 
         let mut inner_trapped = false;
 
@@ -166,9 +159,6 @@ mod test {
     #[test]
     fn nested_reraise_trap_test_outer() {
 
-        let sadness_condition : Condition<int,int> =
-            Condition { key: sadness_key };
-
         let mut outer_trapped = false;
 
         do sadness_condition.trap(|_j| {
@@ -184,8 +174,6 @@ mod test {
 
     #[test]
     fn test_default() {
-        let sadness_condition : Condition<int,int> =
-            Condition { key: sadness_key };
 
         let mut trapped = false;
 

src/rustc/middle/check_const.rs

@@ -82,19 +82,30 @@ fn check_expr(sess: Session, def_map: resolve::DefMap,
                               ~"` in a constant expression");
             }
           }
-          expr_path(_) => {
+          expr_path(pth) => {
+            // NB: In the future you might wish to relax this slightly
+            // to handle on-demand instantiation of functions via
+            // foo::<bar> in a const. Currently that is only done on
+            // a path in trans::callee that only works in block contexts.
+            if pth.types.len() != 0 {
+                sess.span_err(
+                    e.span, ~"paths in constants may only refer to \
+                              items without type parameters");
+            }
             match def_map.find(e.id) {
-              Some(def_const(def_id)) => {
+              Some(def_const(def_id)) |
+                Some(def_fn(def_id, _)) => {
                 if !ast_util::is_local(def_id) {
                     sess.span_err(
                         e.span, ~"paths in constants may only refer to \
-                                 crate-local constants");
+                                 crate-local constants or functions");
                 }
               }
               _ => {
                 sess.span_err(
                     e.span,
-                    ~"paths in constants may only refer to constants");
+                    ~"paths in constants may only refer to \
+                      constants or functions");
               }
             }
           }

src/rustc/middle/trans/base.rs

@@ -2688,6 +2688,7 @@ fn trans_crate(sess: session::Session,
           vtables: map::HashMap(),
           const_cstr_cache: HashMap(),
           const_globals: HashMap(),
+          const_values: HashMap(),
           module_data: HashMap(),
           lltypes: ty::new_ty_hash(),
           names: new_namegen(sess.parse_sess.interner),

src/rustc/middle/trans/common.rs

@@ -140,10 +140,19 @@ type crate_ctxt = {
      vtables: HashMap<mono_id, ValueRef>,
      // Cache of constant strings,
      const_cstr_cache: HashMap<~str, ValueRef>,
-     // Reverse-direction for const ptrs cast from globals,
-     // since the ptr -> init association is lost any
-     // time a GlobalValue is cast.
+
+     // Reverse-direction for const ptrs cast from globals.
+     // Key is an int, cast from a ValueRef holding a *T,
+     // Val is a ValueRef holding a *[T].
+     //
+     // Needed because LLVM loses pointer->pointee association
+     // when we ptrcast, and we have to ptrcast during translation
+     // of a [T] const because we form a slice, a [*T,int] pair, not
+     // a pointer to an LLVM array type.
      const_globals: HashMap<int, ValueRef>,
+
+     // Cache of emitted const values
+     const_values: HashMap<ast::node_id, ValueRef>,
      module_data: HashMap<~str, ValueRef>,
      lltypes: HashMap<ty::t, TypeRef>,
      names: namegen,

src/rustc/middle/trans/consts.rs

@@ -28,10 +28,6 @@ fn const_lit(cx: @crate_ctxt, e: @ast::expr, lit: ast::lit)
     }
 }
 
-// FIXME (#2530): this should do some structural hash-consing to avoid
-// duplicate constants. I think. Maybe LLVM has a magical mode that does so
-// later on?
-
 fn const_ptrcast(cx: @crate_ctxt, a: ValueRef, t: TypeRef) -> ValueRef {
     let b = llvm::LLVMConstPointerCast(a, T_ptr(t));
     assert cx.const_globals.insert(b as int, a);
@@ -341,24 +337,29 @@ fn const_expr(cx: @crate_ctxt, e: @ast::expr) -> ValueRef {
                                 ~"bad const-slice expr")
         }
       }
-      ast::expr_path(_) => {
+      ast::expr_path(pth) => {
+        assert pth.types.len() == 0;
         match cx.tcx.def_map.find(e.id) {
+          Some(ast::def_fn(def_id, _)) => {
+              assert ast_util::is_local(def_id);
+              let f = base::get_item_val(cx, def_id.node);
+              C_struct(~[f, C_null(T_opaque_box_ptr(cx))])
+          }
           Some(ast::def_const(def_id)) => {
-            // Don't know how to handle external consts
             assert ast_util::is_local(def_id);
-            match cx.tcx.items.get(def_id.node) {
-              ast_map::node_item(@{
-                node: ast::item_const(_, subexpr), _
-              }, _) => {
-                // FIXME (#2530): Instead of recursing here to regenerate
-                // the values for other constants, we should just look up
-                // the already-defined value.
-                const_expr(cx, subexpr)
-              }
-              _ => cx.sess.span_bug(e.span, ~"expected item")
+            if ! cx.const_values.contains_key(def_id.node) {
+                match cx.tcx.items.get(def_id.node) {
+                    ast_map::node_item(@{
+                        node: ast::item_const(_, subexpr), _
+                    }, _) => {
+                        trans_const(cx, subexpr, def_id.node);
+                    }
+                    _ => cx.sess.span_bug(e.span, ~"expected item")
+                }
             }
+            cx.const_values.get(def_id.node)
           }
-          _ => cx.sess.span_bug(e.span, ~"expected to find a const def")
+          _ => cx.sess.span_bug(e.span, ~"expected a const or fn def")
         }
       }
         ast::expr_paren(e) => { return const_expr(cx, e); }
@@ -369,11 +370,9 @@ fn const_expr(cx: @crate_ctxt, e: @ast::expr) -> ValueRef {
 
 fn trans_const(ccx: @crate_ctxt, e: @ast::expr, id: ast::node_id) {
     let _icx = ccx.insn_ctxt("trans_const");
-    let v = const_expr(ccx, e);
-
-    // The scalars come back as 1st class LLVM vals
-    // which we have to stick into global constants.
     let g = base::get_item_val(ccx, id);
+    let v = const_expr(ccx, e);
+    ccx.const_values.insert(id, v);
     llvm::LLVMSetInitializer(g, v);
     llvm::LLVMSetGlobalConstant(g, True);
 }

src/test/run-pass/const-fn-val.rs

@@ -0,0 +1,11 @@
+fn foo() -> int {
+    return 0xca7f000d;
+}
+
+struct Bar { f: &fn() -> int }
+
+const b : Bar = Bar { f: foo };
+
+fn main() {
+    assert (b.f)() == 0xca7f000d;
+}