Summary:
These instructions make a vector of `<4 x float>` by widening every
other lane of a vector of `<8 x half>`.
I wondered about representing these using standard IR, along the lines
of a shufflevector to extract elements of the input into a `<4 x half>`
followed by an `fpext` to turn that into `<4 x float>`. But it looks as
if that would take a lot of work in isel lowering to make it match any
pattern I could sensibly write in Tablegen, and also I haven't been
able to think of any other case where that pattern might be generated
in IR, so there wouldn't be any extra code generation win from doing
it that way.
Therefore, I've just used another target-specific intrinsic. We can
always change it to the other way later if anyone thinks of a good
reason.
(In order to put the intrinsic definition near similar things in
`IntrinsicsARM.td`, I've also lifted the definition of the
`MVEMXPredicated` multiclass higher up the file, without changing it.)
Reviewers: MarkMurrayARM, dmgreen, miyuki, ostannard
Reviewed By: miyuki
Subscribers: kristof.beyls, hiraditya, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D75254
This commit, together with the next few, will add a representative
sample of the kind of IR intrinsics that we'll need in order to
implement the user-facing ACLE intrinsics for MVE. Supporting all of
them will take more work; the intention of this initial series of
commits is to implement an intrinsic or two from lots of different
categories, as examples and proofs of concept.
This initial commit introduces a small number of IR intrinsics for
instructions simple enough that they can use Tablegen ISel patterns:
the predicated versions of the VADD and VSUB instructions (both
integer and FP), VMIN and VMAX, and the float->half VCVT instruction
(predicated and unpredicated).
When using VPT-predicated instructions in automatic code generation,
it will be convenient to specify the predicate value as a vector of
the appropriate number of i1. To make it easy to specify all sizes of
an instruction in one go and give each one the matching predicate
vector type, I've added a system of Tablegen informational records
describing MVE's vector types: each one gives the underlying LLVM IR
ValueType (which may not be the same if the MVE vector is of
explicitly signed or unsigned integers) and an appropriate vNi1 to use
as the predicate vector.
(Also, those info records include the usual encoding for the types, so
that as we add associations between each instruction encoding and one
of the new `MVEVectorVTInfo` records, we can remove some of the
existing template parameters and replace them with references to the
vector type info's fields.)
The user-facing ACLE intrinsics will receive a predicate mask as a
16-bit integer, so I've also provided a pair of intrinsics i2v and
v2i, to convert between an integer and a vector of i1 by just changing
the register class.
Reviewers: dmgreen, miyuki, ostannard
Subscribers: javed.absar, kristof.beyls, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D67158
Simon Tatham