Re: [PATCH] rtl-optimization/110587 - speedup find_hard_regno_for_1

[Jeff Law <jeffreyalaw@gmail.com>]

On 7/31/23 04:54, Richard Biener via Gcc-patches wrote:
> On Tue, 25 Jul 2023, Richard Biener wrote:
> 
>> The following applies a micro-optimization to find_hard_regno_for_1,
>> re-ordering the check so we can easily jump-thread by using an else.
>> This reduces the time spent in this function by 15% for the testcase
>> in the PR.
>>
>> Bootstrap & regtest running on x86_64-unknown-linux-gnu, OK if that
>> passes?
> 
> Ping.
> 
>> Thanks,
>> Richard.
>>
>> 	PR rtl-optimization/110587
>> 	* lra-assigns.cc (find_hard_regno_for_1): Re-order checks.
>> ---
>>   gcc/lra-assigns.cc | 9 +++++----
>>   1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/gcc/lra-assigns.cc b/gcc/lra-assigns.cc
>> index b8582dcafff..d2ebcfd5056 100644
>> --- a/gcc/lra-assigns.cc
>> +++ b/gcc/lra-assigns.cc
>> @@ -522,14 +522,15 @@ find_hard_regno_for_1 (int regno, int *cost, int try_only_hard_regno,
>>   	       r2 != NULL;
>>   	       r2 = r2->start_next)
>>   	    {
>> -	      if (r2->regno >= lra_constraint_new_regno_start
>> +	      if (live_pseudos_reg_renumber[r2->regno] < 0
>> +		  && r2->regno >= lra_constraint_new_regno_start
>>   		  && lra_reg_info[r2->regno].preferred_hard_regno1 >= 0
>> -		  && live_pseudos_reg_renumber[r2->regno] < 0
>>   		  && rclass_intersect_p[regno_allocno_class_array[r2->regno]])
>>   		sparseset_set_bit (conflict_reload_and_inheritance_pseudos,
>>   				   r2->regno);
>> -	      if (live_pseudos_reg_renumber[r2->regno] >= 0
>> -		  && rclass_intersect_p[regno_allocno_class_array[r2->regno]])
>> +	      else if (live_pseudos_reg_renumber[r2->regno] >= 0
>> +		       && rclass_intersect_p
>> +			    [regno_allocno_class_array[r2->regno]])
>>   		sparseset_set_bit (live_range_hard_reg_pseudos, r2->regno);
My biggest concern here would be r2->regno < 0  in the new code which 
could cause an OOB array reference in the first condition of the test.

Isn't that the point if the original ordering?  Test that r2->regno is 
reasonable before using it as an array index?

jeff