Hi!
On 2021-08-09T12:02:02+0200, Richard Biener via Gcc <gcc@gcc.gnu.org> wrote:
> On Fri, Aug 6, 2021 at 6:58 PM Thomas Schwinge <tho...@codesourcery.com>
> wrote:
>> So I'm trying to do some C++... ;-)
>>
>> Given:
>>
>> /* A map from SSA names or var decls to record fields. */
>> typedef hash_map<tree, tree> field_map_t;
>>
>> /* For each propagation record type, this is a map from SSA names or var
>> decls
>> to propagate, to the field in the record type that should be used for
>> transmission and reception. */
>> typedef hash_map<tree, field_map_t> record_field_map_t;
>>
>> Thus, that's a 'hash_map<tree, hash_map<tree, tree>>'. (I may do that,
>> right?) Looking through GCC implementation files, very most of all uses
>> of 'hash_map' boil down to pointer key ('tree', for example) and
>> pointer/integer value.
>
> You could use
>
> hash_map<tree, unsigned> record_field_map_p;
> vec<field_map_t> maps;
>
> and record the index into maps which you record the actual maps.
Ugh ;-) -- yes, if I remember correctly, I've spotted that pattern in a
few GCC source files.
> Alternatively use hash_map<tree, field_map_t *>
ACK; see commit 049eda8274b7394523238b17ab12c3e2889f253e "Avoid 'GTY' use
for 'gcc/omp-oacc-neuter-broadcast.cc:field_map'". (So, actually don't
change 'record_field_map_t' at this time.)
> Note your code will appear to work until you end up in the situation
> where record_field_map_t is resized because hash-map doesn't
> std::move elements when re-hashing.
I'm not understanding, would you please provide some more detail here?
Did you mean "resizing" instead of "re-hashing"? If the latter, then
yes, it does 'std::move' them (via 'hash_table::expand') -- see (your
own) commit 4b9d61f79c0c0185a33048ae6cc72269cf7efa31 "add move CTOR to
auto_vec, use auto_vec for get_loop_exit_edges". But I guess I
completely misunderstood?
Grüße
Thomas
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