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

[Ryan Taylor via llvm-dev]

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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