On February 14, 2016 5:35:13 PM GMT+01:00, Jeff Law <l...@redhat.com> wrote: >On 02/12/2016 10:21 AM, Jeff Law wrote: >>> But really we simply need a better DSE algorithm. >> So the way to fix DSE is to keep the existing algorithm and track the >> hunks of Complex/aggregates that have been set a second time. >> >> My first thought was to implement this as an inverted bitmap. ie, >set >> it to 1 for every byte in the complex/aggregate that is set by the >first >> store. Clear bits for each byte in subsequent stores to the pieces. >If >> the bitmap reaches an empty state, then the initial store is dead. >> >> Adjusting *ref could work too, but would probably be painful if the >> subsequent stores don't happen in a convenient order. >So that was scary easy. We should have done this a long time ago. > >Essentially I call ao_get_ref_base to get the offset/size/max_size >filled in for the first statement. Those are used to initialize the >live bytes bitfield, as long as max_size != -1. > >Then when we have a possible killing statement, we use the ao in a >similar manner to determine which bytes to clear (taking care that the >base is the same between the two references and that in the killing >statement that the size/max_size are the same.). > >When all the live bytes are zero then we've killed the original >statement. > >It's ~20 lines of code. > >I need to pull together some additional tests, but it looks likely >we'll >be able to wrap this up easily for gcc-6.
BTW, we had sth like this before but it had both correctness and more importantly scalability issues. Richard. >Jeff
