From 485399a8d5de8a8bb759feacd9e4915055e51cb5 Mon Sep 17 00:00:00 2001
From: Graydon Hoare <graydon@mozilla.com>
Date: Mon, 25 Apr 2011 05:39:18 +0000
Subject: Skip substitution and/or binding when there's no work to do.

---
 src/comp/middle/ty.rs | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

(limited to 'src')

diff --git a/src/comp/middle/ty.rs b/src/comp/middle/ty.rs
index 3e3279ed..2b4a9a78 100644
--- a/src/comp/middle/ty.rs
+++ b/src/comp/middle/ty.rs
@@ -1391,6 +1391,34 @@ fn type_contains_vars(@type_store tystore, t typ) -> bool {
     ret *flag;
 }
 
+fn type_contains_params(@type_store tystore, t typ) -> bool {
+    fn checker(@type_store tystore, @mutable bool flag, t typ) {
+        alt (struct(tystore, typ)) {
+            case (ty_param(_)) { *flag = true; }
+            case (_) { /* fall through */ }
+        }
+    }
+
+    let @mutable bool flag = @mutable false;
+    auto f = bind checker(tystore, flag, _);
+    walk_ty(tystore, f, typ);
+    ret *flag;
+}
+
+fn type_contains_bound_params(@type_store tystore, t typ) -> bool {
+    fn checker(@type_store tystore, @mutable bool flag, t typ) {
+        alt (struct(tystore, typ)) {
+            case (ty_bound_param(_)) { *flag = true; }
+            case (_) { /* fall through */ }
+        }
+    }
+
+    let @mutable bool flag = @mutable false;
+    auto f = bind checker(tystore, flag, _);
+    walk_ty(tystore, f, typ);
+    ret *flag;
+}
+
 // Type accessors for substructures of types
 
 fn ty_fn_args(@type_store tystore, t fty) -> vec[arg] {
@@ -2495,6 +2523,9 @@ fn type_err_to_str(&ty.type_err err) -> str {
 fn substitute_type_params(@type_store tystore,
                           vec[t] bindings,
                           t typ) -> t {
+    if (!type_contains_bound_params(tystore, typ)) {
+        ret typ;
+    }
     fn replacer(@type_store tystore, vec[t] bindings, t typ) -> t {
         alt (struct(tystore, typ)) {
             case (ty_bound_param(?param_index)) {
@@ -2510,6 +2541,9 @@ fn substitute_type_params(@type_store tystore,
 
 // Converts type parameters in a type to bound type parameters.
 fn bind_params_in_type(@type_store tystore, t typ) -> t {
+    if (!type_contains_params(tystore, typ)) {
+        ret typ;
+    }
     fn binder(@type_store tystore, t typ) -> t {
         alt (struct(tystore, typ)) {
             case (ty_bound_param(?index)) {
-- 
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