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

[Ryan Taylor via llvm-dev]

You'd think isBarrier might work but this is a sync mechanism and doesn't
prevent instructions from crossing the barrier that aren't use dependent.

On Tue, Nov 15, 2016 at 11:12 PM, Madhur Amilkanthwar <madhur13490 at gmail.com
> wrote:

> Just a thought. What about putting a dummy barrier between the
> instructions during selectionDAG creation?
>
> On Nov 16, 2016 4:00 AM, "Ryan Taylor via llvm-dev" <
> llvm-dev at lists.llvm.org> wrote:
>
>> Setting the MI as isTerminator  should have the same impact, yes? I'm not
>> sure of the other consequences of this though, if any, have to look into it.
>>
>> Thanks.
>>
>> -Ryan
>>
>> On Tue, Nov 15, 2016 at 5:18 PM, Krzysztof Parzyszek <
>> kparzysz at codeaurora.org> wrote:
>>
>>> You can override TargetInstrInfo::isSchedulingBoundary for that.
>>>
>>> -Krzysztof
>>>
>>> On 11/15/2016 4:13 PM, Ryan Taylor 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 <mailto: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 <mailto:llvm-dev at lists.llvm.org>
>>>>         http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>         <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>>>>
>>>>
>>>>     --
>>>>     Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>>>>     hosted by The Linux Foundation
>>>>     _______________________________________________
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>>>>
>>>>
>>>>
>>> --
>>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>>> hosted by The Linux Foundation
>>>
>>
>>
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