* Store lists as lists of pointers to values rather than as lists of

  values.  This improves sharing and gives another speed up.
  Evaluation of the NixOS system attribute is now almost 7 times
  faster than the old evaluator.

1 files changed, 16 insertions, 11 deletions

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 0d7459feef..ae17506cee 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -311,7 +311,7 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
             if (key == "args") {
                 state.forceList(i->second);
                 for (unsigned int n = 0; n < i->second.list.length; ++n) {
-                    string s = state.coerceToString(i->second.list.elems[n], context, true);
+                    string s = state.coerceToString(*i->second.list.elems[n], context, true);
                     drv.args.push_back(s);
                 }
             }
@@ -651,14 +651,17 @@ static void prim_attrNames(EvalState & state, Value * * args, Value & v)
     state.forceAttrs(*args[0]);
 
     state.mkList(v, args[0]->attrs->size());
+    Value * vs = state.allocValues(v.list.length);
 
     StringSet names;
     foreach (Bindings::iterator, i, *args[0]->attrs)
         names.insert(i->first);
 
     unsigned int n = 0;
-    foreach (StringSet::iterator, i, names)
-        mkString(v.list.elems[n++], *i);
+    foreach (StringSet::iterator, i, names) {
+        v.list.elems[n] = &vs[n];
+        mkString(vs[n++], *i);
+    }
 }
 
 
@@ -701,8 +704,8 @@ static void prim_removeAttrs(EvalState & state, Value * * args, Value & v)
     state.cloneAttrs(*args[0], v);
 
     for (unsigned int i = 0; i < args[1]->list.length; ++i) {
-        state.forceStringNoCtx(args[1]->list.elems[i]);
-        v.attrs->erase(state.symbols.create(args[1]->list.elems[i].string.s));
+        state.forceStringNoCtx(*args[1]->list.elems[i]);
+        v.attrs->erase(state.symbols.create(args[1]->list.elems[i]->string.s));
     }
 }
 
@@ -718,7 +721,7 @@ static void prim_listToAttrs(EvalState & state, Value * * args, Value & v)
     state.mkAttrs(v);
 
     for (unsigned int i = 0; i < args[0]->list.length; ++i) {
-        Value & v2(args[0]->list.elems[i]);
+        Value & v2(*args[0]->list.elems[i]);
         state.forceAttrs(v2);
         
         Bindings::iterator j = v2.attrs->find(state.sName);
@@ -815,8 +818,8 @@ static void prim_head(EvalState & state, Value * * args, Value & v)
     state.forceList(*args[0]);
     if (args[0]->list.length == 0)
         throw Error("`head' called on an empty list");
-    state.forceValue(args[0]->list.elems[0]);
-    v = args[0]->list.elems[0];
+    state.forceValue(*args[0]->list.elems[0]);
+    v = *args[0]->list.elems[0];
 }
 
 
@@ -840,11 +843,13 @@ static void prim_map(EvalState & state, Value * * args, Value & v)
     state.forceList(*args[1]);
 
     state.mkList(v, args[1]->list.length);
+    Value * vs = state.allocValues(v.list.length);
 
     for (unsigned int n = 0; n < v.list.length; ++n) {
-        v.list.elems[n].type = tApp;
-        v.list.elems[n].app.left = args[0];
-        v.list.elems[n].app.right = &args[1]->list.elems[n];
+        v.list.elems[n] = &vs[n];
+        vs[n].type = tApp;
+        vs[n].app.left = args[0];
+        vs[n].app.right = args[1]->list.elems[n];
     }
 }