[Mesa-dev] [PATCH 1/2] glsl: Don't rehash the values when copying to new table

[Tapani Pälli]

On 12/30/2016 05:53 AM, Vladislav Egorov wrote:
> I've looked into it recently (I'm working on series of many various
> trivial optimizations)
>
> and it's faster to just memcpy() it. Just throwing out superfluous
> hashing still keeps slow
>
> hash-table insertion around -- with resizing, rehashing, memory
> allocation/deallocation, internal
>
> hash-function through integer division, collisions and so on. It
> produces a nice speed improvement
>
> actually. It's possible to explore approaches without any copying at
> LOOP/IF entering at all,
>
> but I am not sure it will improve performance.

When profiling copy_propagation(_elements) pass you can use Martina's 
testcase from this bug:

https://bugs.freedesktop.org/show_bug.cgi?id=94477

We still have a very long compile time for the WebGL case mentioned in 
the bug so would be cool to have some optimizations there.


>
> 30.12.2016 02:49, Thomas Helland пишет:
>> Really, we should have some kind of function for copying the whole table,
>> but this will work for now.
>> ---
>>   src/compiler/glsl/opt_copy_propagation.cpp | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/compiler/glsl/opt_copy_propagation.cpp
>> b/src/compiler/glsl/opt_copy_propagation.cpp
>> index 247c498..e9f82e0 100644
>> --- a/src/compiler/glsl/opt_copy_propagation.cpp
>> +++ b/src/compiler/glsl/opt_copy_propagation.cpp
>> @@ -210,7 +210,8 @@
>> ir_copy_propagation_visitor::handle_if_block(exec_list *instructions)
>>      /* Populate the initial acp with a copy of the original */
>>      struct hash_entry *entry;
>>      hash_table_foreach(orig_acp, entry) {
>> -      _mesa_hash_table_insert(acp, entry->key, entry->data);
>> +      _mesa_hash_table_insert_pre_hashed(acp, entry->hash,
>> +                                         entry->key, entry->data);
>>      }
>>        visit_list_elements(this, instructions);
>> @@ -259,7 +260,8 @@ ir_copy_propagation_visitor::handle_loop(ir_loop
>> *ir, bool keep_acp)
>>      if (keep_acp) {
>>         struct hash_entry *entry;
>>         hash_table_foreach(orig_acp, entry) {
>> -         _mesa_hash_table_insert(acp, entry->key, entry->data);
>> +         _mesa_hash_table_insert_pre_hashed(acp, entry->hash,
>> +                                            entry->key, entry->data);
>>         }
>>      }
>>
>
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