Repost: RFA [4.1]: improvement to if-conversion and cross-jumping (PR20070)

[Bernd Schmidt]

Joern RENNECKE wrote:
> Bernd Schmidt wrote:
> 
>>  
>> Nevermind the fact that this has a duplicate call of validate_change. 
>> What is this code trying to do?  I would have naively thought that if 
>> we have R5 and R0 live at the end, then previous uses of either 
>> register must match exactly.
>>
>> Can you post an RTL example of what you're trying to accomplish with 
>> the code related to input_reg?  What can be done with it that can't be 
>> done by examining the local_regs still live at the start of a block?
> 
> 
> input_reg is for a register that is *not* local to the block, but 
> remains unaltered.  In principle, we could also match constants here, 
> but I haven't had sufficient motivation (as in: appears to be relevant 
> to performance according to the benchmarks I've looked at) so far.  We 
> should only encounter it as an rvalue.
> When we are processing REG_NOTES, e..g REG_EQUAL, it is quite possible 
> that we see a note later in the insn stream than the actual last use in 
> insn patterns, i.e. scanning backwards
> we'll see these notes first.  In order to recognize them, we have to use 
> information from a previous pass.

I'll ask again, please post an example or two of the way this is 
intended to work.


Bernd