Add a primop ‘concatLists’

This can serve as a generic efficient list builder.  For instance, the
function ‘catAttrs’ in Nixpkgs can be rewritten from

  attr: l: fold (s: l: if hasAttr attr s then [(getAttr attr s)] ++ l else l) [] l

to

  attr: l: builtins.concatLists (map (s: if hasAttr attr s then [(getAttr attr s)] else []) l)

Statistics before:

  time elapsed: 1.08683
  size of a value: 24
  environments allocated: 1384376 (35809568 bytes)
  list elements: 6946783 (55574264 bytes)
  list concatenations: 37434
  values allocated: 1760440 (42250560 bytes)
  attribute sets allocated: 392040
  right-biased unions: 186334
  values copied in right-biased unions: 591137
  symbols in symbol table: 18273
  number of thunks: 1297673
  number of thunks avoided: 1380759
  number of attr lookups: 430802
  number of primop calls: 628912
  number of function calls: 1333544

Statistics after (including new catAttrs):

  time elapsed: 0.959854
  size of a value: 24
  environments allocated: 1010198 (26829296 bytes)
  list elements: 1984878 (15879024 bytes)
  list concatenations: 30488
  values allocated: 1589760 (38154240 bytes)
  attribute sets allocated: 392040
  right-biased unions: 186334
  values copied in right-biased unions: 591137
  symbols in symbol table: 18274
  number of thunks: 1040925
  number of thunks avoided: 1038428
  number of attr lookups: 438419
  number of primop calls: 474844
  number of function calls: 959366
This commit is contained in:
Eelco Dolstra 2012-08-13 01:53:10 -04:00
parent b9e5b908ed
commit 198d0338be
3 changed files with 33 additions and 8 deletions

View file

@ -912,16 +912,29 @@ void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
void ExprOpConcatLists::eval(EvalState & state, Env & env, Value & v)
{
state.nrListConcats++;
Value v1; e1->eval(state, env, v1);
state.forceList(v1);
Value v2; e2->eval(state, env, v2);
state.forceList(v2);
state.mkList(v, v1.list.length + v2.list.length);
for (unsigned int n = 0; n < v1.list.length; ++n)
v.list.elems[n] = v1.list.elems[n];
for (unsigned int n = 0; n < v2.list.length; ++n)
v.list.elems[n + v1.list.length] = v2.list.elems[n];
Value * lists[2] = { &v1, &v2 };
state.concatLists(v, 2, lists);
}
void EvalState::concatLists(Value & v, unsigned int nrLists, Value * * lists)
{
nrListConcats++;
unsigned int len = 0;
for (unsigned int n = 0; n < nrLists; ++n) {
forceList(*lists[n]);
len += lists[n]->list.length;
}
mkList(v, len);
for (unsigned int n = 0, pos = 0; n < nrLists; ++n) {
unsigned int l = lists[n]->list.length;
memcpy(v.list.elems + pos, lists[n]->list.elems, l * sizeof(Value *));
pos += l;
}
}

View file

@ -232,6 +232,8 @@ public:
void mkAttrs(Value & v, unsigned int expected);
void mkThunk_(Value & v, Expr * expr);
void concatLists(Value & v, unsigned int nrLists, Value * * lists);
/* Print statistics. */
void printStats();

View file

@ -931,6 +931,7 @@ static void prim_filter(EvalState & state, Value * * args, Value & v)
}
/* Return true if a list contains a given element. */
static void prim_elem(EvalState & state, Value * * args, Value & v)
{
bool res = false;
@ -944,6 +945,14 @@ static void prim_elem(EvalState & state, Value * * args, Value & v)
}
/* Concatenate a list of lists. */
static void prim_concatLists(EvalState & state, Value * * args, Value & v)
{
state.forceList(*args[0]);
state.concatLists(v, args[0]->list.length, args[0]->list.elems);
}
/* Return the length of a list. This is an O(1) time operation. */
static void prim_length(EvalState & state, Value * * args, Value & v)
{
@ -1160,6 +1169,7 @@ void EvalState::createBaseEnv()
addPrimOp("map", 2, prim_map);
addPrimOp("__filter", 2, prim_filter);
addPrimOp("__elem", 2, prim_elem);
addPrimOp("__concatLists", 1, prim_concatLists);
addPrimOp("__length", 1, prim_length);
// Integer arithmetic