[PATCH] D72798: [llvm][docs] LangRef for IR attribute `vector-function-abi-variants`.

[Francesco Petrogalli via Phabricator via llvm-commits]

fpetrogalli created this revision.
fpetrogalli added reviewers: jdoerfert, andwar.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72798

Files:
  llvm/docs/LangRef.rst


Index: llvm/docs/LangRef.rst
===================================================================
--- llvm/docs/LangRef.rst
+++ llvm/docs/LangRef.rst
@@ -1841,6 +1841,69 @@
     function has not changed between the function prolog and eiplog. It is
     currently x86_64-specific.
 
+Instruction Attributes
+----------------------
+
+Attributes may be attached to instrucions. The following instruction
+attributes are supported.
+
+``vector-function-abi-variants``
+    This attribute can be attached to a CallInst to list the vector
+    function that can be used to vectorize calls to the scalar
+    function. The Attribute consists of a comma separated list of
+    mangled names. The syntax for the mangled names is as follows:
+
+         _ZGV<isa><mask><vlen><parameters>_<scalar_name>{(<vector_redirection>)}
+
+    When present, the attribute informs the compiler that the function
+    ``<scalar_name>`` has a correspondent vector variant that can be
+    used to perform the concurrent invocation of ``<scalar_name>`` on
+    vectors. The shape of the vector function is described by the
+    tokens between the prefix ``_ZGV`` and the ``<scalar_name>``
+    token. The standard name of the vector function is
+    ``_ZGV<isa><mask><vlen><parameters>_<scalar_name>``. When present,
+    the optional ``(<vector_redirection>)`` informs the compiler that
+    a custom name is provided instead of the standard one
+    ``_ZGV<isa><mask><vlen><parameters>_<scalar_name>``. The
+    definition or declaration of the variant must be present in the IR
+    Module. The signature of the vector variant is determined by the
+    rules of the Vector Function ABI (VFABI) specifications of the
+    target. For Arm and X86, the VFABI can be found at
+    https://github.com/ARM-software/software-standards and
+    https://software.intel.com/en-us/articles/vector-simd-function-abi,
+    respectively.
+
+    For X86 and Arm targets, the values of the tokens in the standard
+    name are those that are defined in the VFABI. The same tokens of
+    X86 and Arm are used to represent the Internal LLVM Vector Isa
+    when ``<isa> = __LLVM__``.
+
+    The tokens are expand as follows:
+
+    <isa>:= b | c | d | e  -> X86 SSE, AVX, AVX2, AVX512
+          | n | s          -> Armv8 Advanced SIMD, SVE
+          | __LLVM__       -> Internal LLVM Vector ISA
+
+    <mask>:= M | N         -> mask | no mask
+
+    <vlen>:= number        -> number of lanes
+           | x             -> VLA (Vector Length Agnostic)
+
+    <parameters>:= v              -> vector
+                 | l | l <number> -> linear
+                 | R | R <number> -> linear with ref modifier
+                 | L | L <number> -> linear with val modifier
+                 | U | U <number> -> linear with uval modifier
+                 | ls <pos>       -> runtime linear
+                 | Rs <pos>       -> runtime linear with ref modifier
+                 | Ls <pos>       -> runtime linear with val modifier
+                 | Us <pos>       -> runtime linear with uval modifier
+                 | u              -> uniform
+
+    <scalar_name>:= name of the scalar function
+
+    <vector_redirection>:= optional, custom name of the vector function
+
 .. _glattrs:
 
 Global Attributes


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