> On Sep 11, 2020, at 3:36 PM, Segher Boessenkool <seg...@kernel.crashing.org>
> wrote:
>
> On Fri, Sep 11, 2020 at 03:17:19PM -0500, Qing Zhao wrote:
>>> On Sep 11, 2020, at 3:05 PM, Segher Boessenkool
>>> <seg...@kernel.crashing.org> wrote:
>>> On Fri, Sep 11, 2020 at 02:40:06PM -0500, Qing Zhao wrote:
>>>>> On Sep 11, 2020, at 12:13 PM, Segher Boessenkool
>>>>> <seg...@kernel.crashing.org> wrote:
>>>>> On Fri, Sep 11, 2020 at 11:52:29AM -0500, Qing Zhao wrote:
>>>>>> I don’t understand why it’s not correct if we clearing call-clobbered
>>>>>> registers
>>>>>> AFTER restoring call-preserved registers?
>>>>>
>>>>> Because the compiler backend (or the linker! Or the dynamic linker!
>>>>> Etc.) can use volatile registers for their own purposes.
>>>>
>>>> For the following sequence at the end of a routine:
>>>>
>>>> *...*
>>>> “restore call-preserved registers”
>>>> *clear call-clobbered registers"*
>>>> *ret*
>>>>
>>>> “Clear call-clobbered registers” will only clear the call-clobbered
>>>> registers that are not live at the end of the routine.
>>>
>>> And they can be written again right after the routine, by linker-
>>> generated code for example. This is a waste.
>>>
>>>> In the new version of the patch, the implementation of clearing
>>>> call-clobbered registers is done in backend, middle end only
>>>> computes a hard register set based on user option, source attribute, data
>>>> flow information, and function abi information, and
>>>> Then pass this hard register set to the target hook to generate the
>>>> clearing sequence. The backend will have all the details
>>>> on the special situations you mentioned.
>>>>
>>>> Let me know any more concerns here.
>>>
>>> I cannot find that patch?
>>
>> Haven’t finished yet. -:).
>
> Ah okay :-)
>
> If you have, please send it in a new thread (not as a reply)? So that
> it will be much easirer to handle :-)
Okay. Will do.
Qing
>
>
> Segher
