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

Matthias Braun via llvm-dev
Thu, 28 Apr 2016 15:37:16 -0000

If it is not a reserved register, then you should have a live interval.
Registers can be non-allocatable but also not reserved, this is true for the
flag registers on most targets (I have no idea about System Z though)

- Matthias

> On Apr 28, 2016, at 1:52 AM, Jonas Paulsson via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
>
> 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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