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Re: C++: Why do we nreverse CLASSTYPE_TAGS
Jason Merrill <jason at redhat dot com> writes:
| On 24 Mar 2003 13:02:26 -0800, Mark Mitchell <mark at codesourcery dot com> wrote:
|
| > On Mon, 2003-03-24 at 11:56, Matt Austern wrote:
| >> On Monday, March 24, 2003, at 11:21 AM, Mark Mitchell wrote:
| >>
| >> >> OK, I'll experiment with that approach. What threasold would you put
| >> >> for "lots"?
| >> >
| >> > I dunno. Probably 10 or so, to start. With fewer than that, hashing
| >> > can't possibly be a win.
| >>
| >> How expensive is the hash function? Unless it's pretty extreme, I'd be
| >> surprised if you needed to get all the way to 10 to get a win.
| >
| > Well, it's a hash *function*; you get to make an extra function call.
| >
| > As opposed to roughly:
| >
| > for (x = TYPE_FIELDS (t); x; x = TREE_CHAIN (x))
| > if (DECL_NAME (x) == name)
| > break;
|
| Something that seems to have been missed in this discussion is that we
| don't currently do a linear search for field lookups. We do a binary
| search, which should be plenty fast.
Yes. However, a linear search is done when looking for nested-types
in decl.c:lookup_tag(). Replacing current_binding_level->tags with a
hash-table turned out to affect CLASSTYPE_TAGS also since we do some
random assignments here and there...
-- Gaby