[llvm-dev] how to prevent LLVM back-end from reordering instructions at instruction scheduling?

[Ehsan Amiri via llvm-dev]

Maybe I missed the point. But from the email, it is not clear to me what is
the reason that what scheduler does is not good. We will need to decide on
the solution after we understand the reason that the reordering is
incorrect.

On Tue, Nov 15, 2016 at 5:13 PM, Ryan Taylor via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I have the same issue, would it be easier and more useful to attach a flag
> to the instruction to tell the scheduler not to move instructions across
> this boundary?
>
> -Ryan
>
> On Tue, Nov 15, 2016 at 5:11 PM, Krzysztof Parzyszek via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> You can create a DAG mutation that adds artificial dependencies between
>> A, B and Z.
>>
>> -Krzysztof
>>
>>
>> On 11/15/2016 3:26 PM, Wei Ding via llvm-dev wrote:
>>
>>> Hello,
>>>
>>> I have a LLVM backend question regarding how to prevent compiler from
>>> reordering instructions. For example, I have the following instructions.
>>> Z_instruction is the one which I want to insert.
>>>
>>>
>>> // instruction order which I am looking for
>>> /////////////////////////////////////////
>>> A_instruction
>>> B_instruction
>>>
>>> *Z_instruction*
>>>
>>> C_instruction
>>> D_instruction
>>> E_instruction
>>> F_instruction
>>>
>>> *Z_instruction*
>>>
>>> G_instruction
>>> F_instruction
>>>
>>>
>>> ==================================================
>>>
>>> But I found compiler reordered those instructions like the following.
>>> How could I prevent compiler from moving *A_instruction* and
>>> *B_instruction* after the first *Z_instruction*? Any recommendations and
>>> suggestion are greatly appreciated here!!!
>>>
>>> *Z_instruction*
>>> *
>>> *
>>> A_instruction
>>> B_instruction
>>>
>>> C_instruction
>>> D_instruction
>>> E_instruction
>>> F_instruction
>>>
>>> *Z_instruction*
>>>
>>> G_instruction
>>> F_instruction
>>>
>>> BTW, I have define input/output chain for : *C_instruction,
>>> D_instruction, E_instruction, F_instruction and Z_instruction*
>>> *
>>> *
>>> Thank you so much!
>>>
>>> --
>>> Wei Ding
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>> --
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>> by The Linux Foundation
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>
>
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