Re: How to describe ‘earlyclobber’ explicitly for specific source operand ?

[Richard Earnshaw]

On 22/11/2021 06:40, Jojo R via Gcc wrote:
> 
> — Jojo
> 在 2021年11月20日 +0800 AM6:11，Peter Bergner <bergner@linux.ibm.com>，写道：
>> On 11/19/21 1:28 AM, Jojo R via Gcc wrote:
>>> We know gcc supply earlyclobber function to avoid register overlap,
>>>
>>> but it can not describe explicitly for specific source operand, is it right ?
>>
>> You add the early clobber to the OUTPUT operand(s) that can clobber any of the
>> input source operands. You don't mark the source operands that could be clobbered.
> Yes, so we need to enhance the early clobber to cover this scene ?
>>
>> Peter

You can write alternatives that explicitly tie a source to the 
destination, provided that the source and destination are the same size. 
  See the Arm backend for examples.

R.