[llvm-dev] Machinepipeliner interface. shouldIgnoreForPipelining, actually not ignoring.

[Jinsong Ji via llvm-dev]

Hi Sander:

It may be confusing, but it is not a bug.
And you are right,  if you are using the in-tree machinepipeliner, it won't
have any effects,
because there is NO In tree reference of this API at all.

You can see the comments when James introduced this API in
https://reviews.llvm.org/D67167



Best,

Jinsong Ji (纪金松), PhD.

XL/LLVM on Power Compiler Development
E-mail: jji at us.ibm.com



From:	Sander via llvm-dev <llvm-dev at lists.llvm.org>
To:	llvm-dev at lists.llvm.org
Date:	06/02/2020 03:47 PM
Subject:	[EXTERNAL] [llvm-dev] Machinepipeliner interface.
            shouldIgnoreForPipelining, actually not ignoring.
Sent by:	"llvm-dev" <llvm-dev-bounces at lists.llvm.org>



Hi all,

I think there is a mistake in the machinepipeliner interface. In the
TargetInstrInfo.h in the class PipelinerLoopInfo there is a function
"bool shouldIgnoreForPipelining(const MachineInstr *MI)". The
description says that if this function returns true for a given
MachineInstr it will not be pipelined.

However in reality it is not ignored and is being considered for
pipelining. I implemented this function in my own backend, and put an
instruction there that I want to be ignored, but still this instruction
end up trying to be pipelined. I implemented the same way as in
PPCInstrInfo.cpp, and I think it has the same bug. Is this a bug, or am
I forgetting something?

Kind regards,

Sander Ruben

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