llvm dev - Sep 2020 - using experimental intrinsics failed

Hi:

Sorry I need to send email directly. I am new to llvm and trying to write
interval arithmetic, which requires changing rounding mode during computation.

The document I
found https://llvm.org/docs/LangRef.html#constrained-floating-point-intrinsics,
seems to be doing the trick. Here is the piece of code that I did:

%5 = call double @llvm.experimental.constrained.fadd(double %0, double %2, metadata !"round.downward", metadata !"fpexcept.ignore")

It is taking the first and third argument and adding them together with the
downward rounding mode. However, when I try to convert it to bit code, I got the
error:

error: use of undefined value '@llvm.experimental.constrained.fadd'

Is there any flags I need to add in order to use this intrinsic? Or this is just
a wrong function call. I am using the llvm version 10.0.1.

Thank you
Xuan Tang
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I think you need a declaration like this at module scope in your IR file.
Everything that's called either needs to be defined or declared even if it
is an intrinsic. It doesn't matter if the declaration is before or after
the use.

*declare double* *@llvm.experimental.constrained.fadd*(*double,* *double*,
*metadata*", *metadata*)

~Craig


On Thu, Sep 3, 2020 at 5:36 PM Xuan Tang via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi:
>
> Sorry I need to send email directly. I am new to llvm and trying to write
> interval arithmetic, which requires changing rounding mode during
> computation.
>
> The document I found
> https://llvm.org/docs/LangRef.html#constrained-floating-point-intrinsics,
> seems to be doing the trick. Here is the piece of code that I did:
>
> *%5* = *call* *double* *@llvm.experimental.constrained.fadd*(*double* *%0*
> , *double* *%2*, *metadata* !"round.downward", *metadata*
!"fpexcept.i
> gnore")
>
> It is taking the first and third argument and adding them together with
> the downward rounding mode. However, when I try to convert it to bit code,
> I got the error:
>
> error: use of undefined value '@llvm.experimental.constrained.fadd'
>
> Is there any flags I need to add in order to use this intrinsic? Or this
> is just a wrong function call. I am using the llvm version 10.0.1.
>
> Thank you
> Xuan Tang
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Hi Craig:

I tried that, now the function is like this:
; Function Attrs: norecurse nounwind readnone ssp uwtable
define { double, double } @add(double, double, double, double)
local_unnamed_addr #0 {
  %5 = call double @llvm.experimental.constrained.fadd(double %0, double %2, metadata !"round.downward", metadata !"fpexcept.ignore")
  %6 = fadd double %1, %3
  %7 = insertvalue { double, double } undef, double %5, 0
  %8 = insertvalue { double, double } %7, double %6, 1
  ret { double, double } %8
}

declare double @llvm.experimental.constrained.fadd(double, double, metadata, metadata)

But now I get the error at the line of declaration:
error: expected function name

I tried the example
at https://llvm.org/docs/LangRef.html#variable-argument-handling-intrinsics and
that compiles fine, which means the declaration code should work as well.

Thank you
Xuan Tang
On Sep 3, 2020, 19:41 -0500, Craig Topper <craig.topper at gmail.com>,
wrote:
> I think you need a declaration like this at module scope in your IR file.
Everything that's called either needs to be defined or declared even if it
is an intrinsic. It doesn't matter if the declaration is before or after the
use.
>
> declare
double @llvm.experimental.constrained.fadd(double, double, metadata", metadata)
>
> ~Craig
>
>
> > On Thu, Sep 3, 2020 at 5:36 PM Xuan Tang via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> > > Hi:
> > >
> > > Sorry I need to send email directly. I am new to llvm and trying
to write interval arithmetic, which requires changing rounding mode during
computation.
> > >
> > > The document I
found https://llvm.org/docs/LangRef.html#constrained-floating-point-intrinsics,
seems to be doing the trick. Here is the piece of code that I did:
> > >
> > >
%5 = call double @llvm.experimental.constrained.fadd(double %0, double %2, metadata !"round.downward", metadata !"fpexcept.ignore")
> > >
> > > It is taking the first and third argument and adding them
together with the downward rounding mode. However, when I try to convert it to
bit code, I got the error:
> > >
> > > error: use of undefined value
'@llvm.experimental.constrained.fadd'
> > >
> > > Is there any flags I need to add in order to use this intrinsic?
Or this is just a wrong function call. I am using the llvm version 10.0.1.
> > >
> > > Thank you
> > > Xuan Tang
> > > _______________________________________________
> > > LLVM Developers mailing list
> > > llvm-dev at lists.llvm.org
> > > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Note that the intrinsics don’t affect the rounding mode at run time.

What they do is the tell llvm what rounding mode llvm should expect the code to
be using when it does eventually get run. You’ll need to change the rounding
mode in your fp environment yourself by calling fpsetround() or whatever your
system uses.

Also, note that the work to implement the constrained intrinsics is ongoing.
Some hosts support it (X86, SystemZ, and recently PowerPC), but roughly no
optimizations are enabled yet. So don’t expect performance yet.

I apologize for being behind in my email.
--
Kevin P. Neal
SAS/C and SAS/C++ Compiler
Compute Services
SAS Institute, Inc.



From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Xuan Tang
via llvm-dev
Sent: Thursday, September 03, 2020 2:46 AM
To: llvm-dev at lists.llvm.org
Subject: [llvm-dev] using experimental intrinsics failed


EXTERNAL
Hi:

Sorry I need to send email directly. I am new to llvm and trying to write
interval arithmetic, which requires changing rounding mode during computation.

The document I found
https://llvm.org/docs/LangRef.html#constrained-floating-point-intrinsics<https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fllvm.org%2Fdocs%2FLangRef.html%23constrained-floating-point-intrinsics&data=02%7C01%7Ckevin.neal%40sas.com%7C56cf4859d8c74a71fee008d8506a9f99%7Cb1c14d5c362545b3a4309552373a0c2f%7C0%7C0%7C637347766165256247&sdata=1L%2FOWIXGU%2BLZZwCr5T1SaoPFEY%2FBwF10V6azvtyHs2I%3D&reserved=0>,
seems to be doing the trick. Here is the piece of code that I did:

%5 = call double @llvm.experimental.constrained.fadd(double %0, double %2,
metadata !"round.downward", metadata !"fpexcept.ignore")

It is taking the first and third argument and adding them together with the
downward rounding mode. However, when I try to convert it to bit code, I got the
error:

error: use of undefined value '@llvm.experimental.constrained.fadd'

Is there any flags I need to add in order to use this intrinsic? Or this is just
a wrong function call. I am using the llvm version 10.0.1.

Thank you
Xuan Tang
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