On Sat, Jan 13, 2018 at 2:48 PM, Jeff Law wrote:
> On 01/12/2018 01:58 PM, li...@coryfields.com wrote:
>> From: Cory Fields
>>
>> 2018-01-12 Cory Fields
>>* tree-ira.c (allocno_hard_regs_compare): stabilize sort
>> ---
>> gcc/ChangeLog | 3 +++
>> gcc/ira-color.c | 3 +--
>> 2 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
>> index ab96bd6..546e84c 100644
>> --- a/gcc/ChangeLog
>> +++ b/gcc/ChangeLog
>> @@ -1,4 +1,7 @@
>> 2018-01-12 Cory Fields
>> + * tree-ira.c (allocno_hard_regs_compare): stabilize sort
> Note I'm not sure this is sufficient to stabilize the sort. Given two
> allocnos with the same cost and the same potential hard reg set ought to
> hash to the same value.
>
If the set and cost are the same, then the two allocno_hard_regs are
bit-for-bit identical, so returning 0 in that case is fine. Or have I
misunderstood you?
> Similarly if two sets with the same cost had a hash collision.
A hash collision would cause breakage here, yes. I'd be happy to
change it to a full memcmp-like compare, it just wasn't obvious to me
how to do so.
>
> But it's still more stable than doing nothing.
Agreed, it's enough to fix my bootstrap issues, at least.
Side-note: I just noticed that I wrote the wrong filename in the
changelog/commit msg. I assume those entries will likely change anyway
if committed, but please let me know if I should re-send.
Cory
