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

[Francesco Petrogalli via Phabricator via llvm-commits]

fpetrogalli updated this revision to Diff 238551.
fpetrogalli marked 8 inline comments as done.
fpetrogalli added a comment.

Update text according to review.


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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 +1841,73 @@
     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
+    functions 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 corresponding 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 token ``(<vector_redirection>)`` informs the compiler
+    that a custom name is provided instead of the standard one
+    ``_ZGV<isa><mask><vlen><parameters>_<scalar_name>`` (custom names
+    can be provided for example via the use of ``declare variant`` in
+    OpenMP 5.0). The 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. LLVM has an internal
+    ``<isa>`` token that can be used to create scalar-to-vector
+    mappings for functions that are not directly reconducible to any
+    of the target ISAs (for example, some of the mappings stored in
+    the TargetLibraryInfo). Valid values for the ``<isa>`` token are:
+
+    <isa>:= b | c | d | e  -> X86 SSE, AVX, AVX2, AVX512
+          | n | s          -> Armv8 Advanced SIMD, SVE
+          | __LLVM__       -> Internal LLVM Vector ISA
+    
+    For all targets (x86, Arm and Internal LLVM), the remaining tokens
+    can have the following values:
+
+    <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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