llvm dev - Apr 2018 - [llvm] Query the target from an opt pass?

I'm working on the #pragma STDC FENV_ACCESS ON support, specifically
the support for a strict version of the FP to unsigned int conversion.

I've got a pass that runs and converts a new intrinsic into code that
uses the FP to signed int conversion code similar to how SelectionDAG
handles this now. Except that SelectionDAG will let the target handle
it if the target says it will.

How do I, from an "optimization" pass, query the target to see if it
already has a better way of handling exactly this case? I grepped around
and I didn't see anything in a pass that looked like what I need.

Oh, and the reason I did this as a pass is because I need to add branches,
which means splitting basic blocks. I don't think I can do this in
SelectionDAG.

--
Kevin P. Neal
SAS/C and SAS/C++ Compiler
Host Research and Development
SAS Institute, Inc.




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On 4/3/2018 9:25 AM, Kevin Neal via llvm-dev wrote:
> I'm working on the #pragma STDC FENV_ACCESS ON support, specifically
> the support for a strict version of the FP to unsigned int conversion.
> I've got a pass that runs and converts a new intrinsic into code that
> uses the FP to signed int conversion code similar to how SelectionDAG
> handles this now. Except that SelectionDAG will let the target handle
> it if the target says it will.
> How do I, from an "optimization" pass, query the target to see if
it
> already has a better way of handling exactly this case? I grepped around
> and I didn't see anything in a pass that looked like what I need.
TargetTransformInfo is probably what you're looking for.

-Eli

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
Foundation Collaborative Project

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Hmmm, a quick look at the documentation for TargetTransformInfo doesn't look
like it.

In LegalizeDAG.cpp it uses TLI.getOperationAction() to find out if an SDNode
should be expanded by the legalizer or passed down to the target. That's
what
I need to know, but I need it in a pass pre-legalization.

This seems like weird layering, though. Having an "optimization" pass
be
looking into specific types of SDNode doesn't seem ideal. But I need to
introduce branches, and I don't think I can do that in the SelectionDAG.
Branches in the middle of a basic block seems ... incorrect. Is there a
good way to get ahold of the correct TargetLoweringBase from a pass? But
there's still the layering issue, no?

Oh, and sorry for the top posting. This is the email client I'm stuck with.

From: Friedman, Eli [mailto:efriedma at codeaurora.org]
Sent: Tuesday, April 03, 2018 1:56 PM
To: Kevin Neal <Kevin.Neal at sas.com>; llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] [llvm] Query the target from an opt pass?


EXTERNAL
On 4/3/2018 9:25 AM, Kevin Neal via llvm-dev wrote:
I'm working on the #pragma STDC FENV_ACCESS ON support, specifically
the support for a strict version of the FP to unsigned int conversion.

I've got a pass that runs and converts a new intrinsic into code that
uses the FP to signed int conversion code similar to how SelectionDAG
handles this now. Except that SelectionDAG will let the target handle
it if the target says it will.

How do I, from an "optimization" pass, query the target to see if it
already has a better way of handling exactly this case? I grepped around
and I didn't see anything in a pass that looked like what I need.

TargetTransformInfo is probably what you're looking for.

-Eli


--

Employee of Qualcomm Innovation Center, Inc.

Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
Foundation Collaborative Project
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I think you want to start from TargetMachine and then find an appropriate place
to add a new interface function from there. You'll want to pass a pointer to
the target machine to your pass' constructor via the create function. You
probably want to create your pass from TargetPassConfig::addISelPrepare(). If
you look at that function you'll find some other passes that use a
TargetMachine argument.

-Andy

From: Kevin Neal [mailto:Kevin.Neal at sas.com]
Sent: Tuesday, April 03, 2018 9:25 AM
To: llvm-dev at lists.llvm.org
Cc: Kaylor, Andrew <andrew.kaylor at intel.com>
Subject: [llvm] Query the target from an opt pass?

I'm working on the #pragma STDC FENV_ACCESS ON support, specifically
the support for a strict version of the FP to unsigned int conversion.

I've got a pass that runs and converts a new intrinsic into code that
uses the FP to signed int conversion code similar to how SelectionDAG
handles this now. Except that SelectionDAG will let the target handle
it if the target says it will.

How do I, from an "optimization" pass, query the target to see if it
already has a better way of handling exactly this case? I grepped around
and I didn't see anything in a pass that looked like what I need.

Oh, and the reason I did this as a pass is because I need to add branches,
which means splitting basic blocks. I don't think I can do this in
SelectionDAG.

--
Kevin P. Neal
SAS/C and SAS/C++ Compiler
Host Research and Development
SAS Institute, Inc.




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