[llvm-dev] [RFC] Optional parameter tuples (original) (raw)

Neil Henning via llvm-dev llvm-dev at lists.llvm.org
Wed Feb 12 02:40:14 PST 2020

Hey Simon,

It wasn't clear from your RFC: why can't you just have these optional parameter tuples be normal function arguments to the intrinsics?

Cheers, -Neil.

On Wed, Feb 12, 2020 at 9:28 AM Simon Moll via llvm-dev < llvm-dev at lists.llvm.org> wrote:

Hi,

this is an RFC for optional, named parameter tuples for intrinsics. The proposed syntax is: %z = call @llvm.some.intrinsic(%a, %b) optionaltuple(%x, %y, %z) where from the perspective of the call site %x, %y and %z are simply additional parameters. Optional parameter tuples would be very useful for constrained fp intrinsics and vector predication. Some examples: ; Default fpenv fadd (isomorphic to the fadd instruction) %z = call double @llvm.fadd(%a, %b) ; Constrained fp add %x = call double @llvm.fadd(%a, %b) fpenv(metadata !fpround.tonearest, metadata !fpexcept.strict) ; Constrained fp add with vector predication (https://reviews.llvm.org/D57504) %x = call <256 x double> @llvm.fadd(%a, %b) mask(<256 x i1> %mask), evl(i32 %evl), fpenv(metadata !fpround.tozero, metadata !fpexcept.strict) For constrained fp and VP, we only require a very restricted form of this. That is: - Tuples are only allowed on intrinsic function calls. - There is a builtin list of allowed tuple types (eg tablegen file). - Tuple types are opt in: Intrinsics define a list of permissible tuple types. - Tuple parameters have default values when a tuple is absent at a call site. Eg, for fpenv the default fp environment fpenv(fpround.tonearest,_ _fpexcept.ignore) is implied in the first example above.

Btw, different to operand bundles, optional parameter tuples are much more restricted and do not imply side effects of any kind. We might want to re-use the OpBundle logic for this though. There are probably more use cases for this and i'd like to hear about them. Looking forward to your feedback - Simon

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