I'm always forgetting something, now it was the changelog, see attached
(same as old, nothing significant changed).
On Fri, 3 Aug 2012, Dimitrios Apostolou wrote:
Hi, I've updated this patch to trunk and rebootstrapped it, so I'm
resubmitting it, I'm also making a try to CC all relevant maintainers, sorry
for spamming but even though this patch is simple, it touches many parts.
I'm also adding stats to pointer_{set,map} but it will come in a separate
patch. The notes quoted from earlier mail still apply:
On Sun, 8 Jul 2012, Dimitrios Apostolou wrote:
Hi,
This patch adds many nice stats about hash tables when gcc is run with
-fmem-report. Attached patch tested on x86, no regressions.
Also attached is sample output of -fmem-report when compiling reload.c with
-O2 -g. Especially interesting is the extreme htab usage in var-tracking
(ofcourse we already knew that... :-) and maybe symtab's slightly high
collision rate (given it's a very hot hash table). Moreover it's notable
that since last year, collision rate for mem_attrs_htab has been reduced
from around 8 to 1, still not good enough but major improvement.
Jan: It has negligible overhead in runtime, that's why I'm pushing it again
as it is. Having compile-time instrumentation is something different, but
still I'm not quite sure if it's worth the effort. IMHO doing separate
builds to get memory info is tedious and even I've stopped doing them. If
it has no overhead maybe it's better as a runtime option?
Any way, compile-time instrumentation can come later.
Finally I repost some of my notes I'd like to get feedback on:
* Is it OK that I included <assert.h> in libiberty's hashtab.c? What's the
proper way to assert stuff, since gcc_assert() is not accessible?
* Many hash tables are created with htab_create_ggc(), for example
referenced_vars and default_defs in tree-ssa.c. I collect statistics in
delete_tree_ssa() but maybe some are not deallocated in there but
automatically garbage collected?
* Obviously hash table sizes are inflated where two entries might reference
the same element (for example in symtab_hash) but I don't handle this.
* Changes that reduce load factor have been backed out since they brought
controversy. I still think they are good, at least for symtab. I'll measure
numbers separately for this after this patch makes it.
Thanks,
Dimitris
2012-05-21 Dimitrios Apostolou <ji...@gmx.net>
Print various statistics about hash tables when called with
-fmem-report. If the tables are created once use
htab_dump_statistics(), if they are created/destroyed multiple
times then introduce global variables to track statistics.
* cgraph.c, cgraph.h:
(cgraph_dump_stats): New function to dump stats about hash tables.
* gcc/symtab.c, cgraph.h:
(symtab_dump_stats): New function to dump stats about hash tables.
* cgraph.c: (call_site_hash_{num,expands,searches,collisions}):
New globals to keep statistics about call_site_hash hash tables.
(cgraph_remove_node_callees,cgraph_remove_node): if (mem_report)
then keep statistics about hash tables.
* cselib.c, cselib.h (cselib_dump_stats): New function to dump
stats about cselib_hash_table.
* cselib.c (cselib_htab_{num,expands,searches,collisions}): New
globals to keep hash table statistics.
(cselib_finish): if (mem_report) keep hash table statistics.
* dwarf2out.c (dwarf2out_finish): Call htab_dump_statistics() if
-fmem_report.
* emit-rtl.c, emit-rtl.h (mem_attrs_dump_stats): New function to
dump statistics about mem_attrs_htab hash table.
* tree.h, tree-ssa.c (tree_ssa_dump_stats): New function to print
statistics about all referenced_vars and default_defs hash tables.
* tree-ssa.c (default_defs_{num,expands,searches,collisions})
(referenced_vars_{num,expands,searches,collisions}): new globals
to keep statistics about hash tables.
(delete_tree_ssa): Keep statistics for hash tables by
increasing the new global variables.
* tree.c (dump_tree_statistics): Call tree_ssa_dump_stats().
(print_type_hash_statistics): Used the new htab_dump_statistics()
function.
* var-tracking.c (vars_htab_{num,expands,searches,collisions})
(dropval_htab_{num,expands,searches,collisions})
(cv_htab_{num,expands,searches,collisions}): new globals to keep
hash table statistics.
(shared_hash_destroy, vt_finalize): Keep statistics by
increasing values of new global variables if -fmem-report.
* var-tracking.c, rtl.h (vt_dump_stats): New function to dump
stats about vars->htab, dropped_variables and value_chains hash
tables.
* toplev.c: Included cselib.h for cselib_dump_stats().
(dump_memory_report): Call all the above functions to provide
better statistics.
* hashtab.c, hashtab.h: Added "expands" variable to htab_t for
tracking total times the hash table was expanded.
* hashtab.c, hashtab.h (htab_dump_statistics, htab_collisions_num)
(htab_searches_num, htab_expands_num): New functions for statistics.
* hashtab.c: Included assert.h for checks in htab_dump_statistics.
* cgraph.h, varpool.c (varpool_dump_stats): New function to dump
stats about varpool_hash hash table.
* libcpp/symtab.c, symtab.h: Added "expands" variable to
hash_table type for tracking total times the hash table was
expanded.
* symtab.c (ht_dump_statistics): Beautified stats output.
