[patch] combine ICE fix

Mike Stump mikestump@comcast.net
Tue Dec 3 18:52:00 GMT 2013


On Dec 2, 2013, at 10:26 PM, Jeff Law <law@redhat.com> wrote:
> On 11/27/13 17:13, Cesar Philippidis wrote:
>> 
>> I looked into adding support for incremental DF scanning from df*.[ch]
>> in combine but there are a couple of problems. First of all, combine
>> does its own DF analysis. It does so because its usage falls under this
>> category (df-core.c):
>> 
>>    c) If the pass modifies insns several times, this incremental
>>       updating may be expensive.
>> 
>> Furthermore, combine's DF relies on the DF scanning to be deferred, so
>> the DF_REF_DEF_COUNT values would be off. Eg, calls to SET_INSN_DELETED
>> take place before it updates the notes for those insns. Also, combine
>> has a tendency to undo its changes occasionally.
> I think at this stage of the release cycle, converting combine to incremental DF is probably a no-go.  However, we should keep it in mind for the future -- while hairy I'd really like to see that happen in the long term.

I think Kenny has some thoughts in this area.  I'll cc him to ensure he sees it.


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