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| author | Jan Hubicka <jh@suse.cz> | 2020-05-22 12:31:34 +0200 |
|---|---|---|
| committer | Jan Hubicka <jh@suse.cz> | 2020-08-13 17:49:07 +0200 |
| commit | d575fa7a3abf3b25afb93a39e9a297f6045dc7aa (patch) | |
| tree | 20290c300e151a7bd5ca60ef27e61e03268d94fc | |
| parent | ff05169a0d8bd8d7c6d4ae7eb97d188b45ad4881 (diff) | |
| download | gcc-d575fa7a3abf3b25afb93a39e9a297f6045dc7aa.tar.gz | |
Fix hashing of prestreamed nodes
this patch seems to solve basically all collisions while building cc1.
From:
[WPA] read 3312246 unshared trees
[WPA] read 1144381 mergeable SCCs of average size 4.833785
[WPA] 8843938 tree bodies read in total
[WPA] tree SCC table: size 524287, 197767 elements, collision ratio: 0.506446
[WPA] tree SCC max chain length 43 (size 1)
[WPA] Compared 946614 SCCs, 775077 collisions (0.818789)
to
[WPA] read 3314520 unshared trees
[WPA] read 1144763 mergeable SCCs of average size 4.835021
[WPA] 8849473 tree bodies read in total
[WPA] tree SCC table: size 524287, 200574 elements, collision ratio: 0.486418
[WPA] tree SCC max chain length 2 (size 1)
[WPA] Compared 944189 SCCs, 179 collisions (0.000190)
The problem is that preloaded nodes all have hash code 0 because
cache->nodes.length is not updated while streaming out.
I also added an arbitrary constant to avoid clash with constant of 0 used to
hash NULL pointers and 1 used to hash pointers inside SCC.
* tree-streamer.c (record_common_node): Fix hash value of pre-streamed
nodes.
(cherry picked from commit 1089a367c4b05b5e3f072adca8913904ed65928c)
(cherry picked from commit 5c7ed52a039cfafb63c27fa8c1535e02dfc1ae09)
| -rw-r--r-- | gcc/tree-streamer.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/gcc/tree-streamer.c b/gcc/tree-streamer.c index f6181fafc4c..b0afa1dc6c0 100644 --- a/gcc/tree-streamer.c +++ b/gcc/tree-streamer.c @@ -299,10 +299,11 @@ record_common_node (struct streamer_tree_cache_d *cache, tree node) if (!node) node = error_mark_node; - /* ??? FIXME, devise a better hash value. But the hash needs to be equal - for all frontend and lto1 invocations. So just use the position - in the cache as hash value. */ - streamer_tree_cache_append (cache, node, cache->nodes.length ()); + /* This hash needs to be equal for all frontend and lto1 invocations. So + just use the position in the cache as hash value. + Small integers are used by hash_tree to record positions within scc + hash. Values are not in same range. */ + streamer_tree_cache_append (cache, node, cache->next_idx + 0xc001); switch (TREE_CODE (node)) { |