[llvm-dev] phys reg liveness during foldMemoryOperandImpl()

Jonas Paulsson via llvm-dev
Thu, 28 Apr 2016 08:52:26 -0000

Does that mean that there is a LiveInterval created for all def-uses of
physical registers? While looking quickly, I only saw a method for
preg-arguments constructing such LIs. Not sure if it is done for e.g. a
compare - branch sequence, for the CC reg?

/Jonas


On 2016-04-27 23:31, Matthias Braun wrote:
> I would expect that it shouldn't be too hard to pass around a reference
to LiveIntervalAnalysis*. Patches welcome :)
>
> - Matthias
>
>> On Apr 27, 2016, at 11:38 AM, Jonas Paulsson via llvm-dev <llvm-dev
at lists.llvm.org> wrote:
>>
>> ping.
>>
>> Either this can be implemented easily, or the current SystemZ
optimization LAY -> AGSI in foldMemoryOperandImpl() should be removed, since
this is actually illegal.
>>
>> /Jonas
>>
>> On 2016-04-15 12:53, Jonas Paulsson wrote:
>>> Hi,
>>>
>>> I wonder if it would be possible to extend foldMemoryOperandImp()
so that targets can check for liveness of a particular phys reg?
>>>
>>> The case I am thinking of is when the new instruction clobbers the
CC reg, while the old one did not. In this case the new instruction can only
become a replacement if the CC reg is known to be dead.
>>>
>>> The idea is that liveness of phys regs should be available somehow
when this functionis called during regalloc. Part of the issue is the fact that
CC reg is not an allocatable register.
>>>
>>> /Jonas Paulsson
>>>
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