[PATCH] D108679: Restrict ARM IT Blocks on Windows

Tue Aug 31 14:06:27 PDT 2021

dpaoliello abandoned this revision.
dpaoliello added a comment.

In D108679#2972326 <https://reviews.llvm.org/D108679#2972326>, @kristof.beyls wrote:

> In D108679#2965397 <https://reviews.llvm.org/D108679#2965397>, @dpaoliello wrote:
>
>> In D108679#2964617 <https://reviews.llvm.org/D108679#2964617>, @kristof.beyls wrote:
>>
>>> The performance deprecation of certain forms of IT blocks has been reverted.
>>> The performance deprecation notes are being removed from the Arm ARM.
>>> I am expecting that in the near future, code generation for Arm will be adapted to not enable -mrestrict-it by default at all, following what was already done in gcc at https://gcc.gnu.org/legacy-ml/gcc-patches/2019-12/msg00134.html.
>>>
>>> As such, I'm not sure if this patch is a good thing to implement.
>>> Maybe the guidelines in Microsoft's document you point to (https://docs.microsoft.com/en-us/cpp/build/overview-of-arm-abi-conventions?view=msvc-160#it-instructions) should be adapted to take into account the above described changes to the ArmARM?
>>
>> @kristof.beyls Can you please point me to any official documentation or announcement from ARM about this (I've tried looking myself but couldn't see anything)?
>> I'd be happy to abandon this change and get the Microsoft docs updated if these instructions are no longer deprecated.
>
> I have not found a direct public announcement from Arm about this.
> The "performance deprecation for certain forms of IT blocks" notes in the Arm Architecture Reference Manual (ArmARM) should have been all removed from the latest version at https://developer.arm.com/documentation/ddi0487/latest
> I've found that a few places were missed and raised a defect against the Arm Architecture Reference Manual to get them all removed.
> AFAIK, not having these "performance deprecation" notes in the ArmARM may end up being the only documentation about this.

Looks like you're right: I'm going to go ahead and abandon this change.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D108679/new/

https://reviews.llvm.org/D108679