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Re: [RFC, PATCH]: Introduction of callgraph annotation class
- From: Martin LiÅka <mliska at suse dot cz>
- To: gcc-patches at gcc dot gnu dot org
- Date: Thu, 16 Oct 2014 13:42:18 +0200
- Subject: Re: [RFC, PATCH]: Introduction of callgraph annotation class
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- References: <543EA03A dot 7000000 at suse dot cz> <CAFiYyc12P-DMR=7otSYN+G6DJLK=y+EN7c4sBFZBk1=Lgz9Mzw at mail dot gmail dot com>
On 10/16/2014 01:31 PM, Richard Biener wrote:
On Wed, Oct 15, 2014 at 6:26 PM, Martin LiÅka <email@example.com> wrote:
Following patch introduces a new class called callgraph_annotation. Idea
behind the patch is to provide a generic interface one can use to register
custom info related to a cgraph_node. As you know, symbol_table provides
hooks for creation, deletion and duplication of a cgraph_node. If you have a
pass, you need to handle all these hooks and store custom data in your data
As an example, after discussion with Martin, I chose usage in ipa-prop.h:
if the pass handles an event, following chunk is executed:
if (ipa_node_params_vector.length () <= (unsigned) symtab->cgraph_max_uid)
ipa_node_params_vector.safe_grow_cleared (symtab->cgraph_max_uid + 1);
The problem is that you can have sparse UIDs of cgraph_nodes and every time
you have to allocate a vector of size equal to cgraph_max_uid.
As a replacement, I implemented first version of cgraph_annotation that
internally uses hash_map<cgraph_unique_identifier, T>.
Every time a node is deleted, we remove corresponding data associated to the
What do you think about it?
I don't like "generic annotation" facilities at all. Would it be possible
to make cgraph UIDs not sparse? (keep a free-list of cgraph nodes
with UID < cgraph_max_uid, only really free nodes at the end)
Using a different data structure than a vector indexed by cgraph UID
should also be easily possible (a map from UID to data, hash_map <int, T>).
If I recall correctly, we recycle cgraph_nodes and it's possible that an UID is given to different nodes:
symbol_table::allocate_cgraph_symbol (void). Such uid is problematic from perspective that it cannot be used as a index to a vector.
It was also Honza's note that one can choose inner implementation of such annotation class. We can implement both sparse (hash_map) and consecutive vector data structure.
According to first numbers I was given, Inkscape allocates about ~64k cgraph_nodes in WPA. After function merging is processed, it shrinks to about a half. So that, our free list contains the half of nodes. If we use consecutive vector, our memory impact is bigger thank necessary.