'hw' Dialect

Types and operations for the hardware dialect This dialect defines the hw dialect, which is intended to be a generic representation of HW outside of a particular use-case.

Operation definition

hw.array_concat (::circt::hw::ArrayConcatOp)

Concatenate some arrays

Syntax:

operation ::= `hw.array_concat` $inputs attr-dict `:` custom<ArrayConcatTypes>(type($inputs), qualified(type($result)))

Creates an array by concatenating a variable set of arrays. One or more values must be listed.

// %a, %b, %c are hw arrays of i4 with sizes 2, 5, and 4 respectively.
%array = hw.array_concat %a, %b, %c : (2, 5, 4 x i4)
// %array is !hw.array<11 x i4>

See the HW-SV rationale document for details on operand ordering.

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Operands:

Results:

hw.array_create (::circt::hw::ArrayCreateOp)

Create an array from values

Creates an array from a variable set of values. One or more values must be listed.

// %a, %b, %c are all i4
%array = hw.array_create %a, %b, %c : i4

See the HW-SV rationale document for details on operand ordering.

Traits: SameTypeOperands

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Operands:

Results:

hw.array_get (::circt::hw::ArrayGetOp)

Get the value in an array at the specified index

Syntax:

operation ::= `hw.array_get` $input`[`$index`]` attr-dict `:` qualified(type($input))

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Operands:

Results:

hw.array_slice (::circt::hw::ArraySliceOp)

Get a range of values from an array

Syntax:

operation ::= `hw.array_slice` $input`[`$lowIndex`]` attr-dict `:`
              `(` custom<SliceTypes>(type($input), qualified(type($lowIndex))) `)` `->` qualified(type($dst))

Extracts a sub-range from an array. The range is from lowIndex to lowIndex + the number of elements in the return type, non-inclusive on the high end. For instance,

// Slices 16 elements starting at '%offset'.
%subArray = hw.slice %largerArray at %offset :
    (!hw.array<1024xi8>) -> !hw.array<16xi8>

Would translate to the following SystemVerilog:

logic [7:0][15:0] subArray = largerArray[offset +: 16];

Width of ‘idx’ is defined to be the precise number of bits required to index the ‘input’ array. More precisely: for an input array of size M, the width of ‘idx’ is ceil(log2(M)). Lower and upper bound indexes which are larger than the size of the ‘input’ array results in undefined behavior.

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Operands:

Results:

hw.bitcast (::circt::hw::BitcastOp)

Reinterpret one value to another value of the same size and
potentially different type.  See the `hw` dialect rationale document for
more details.

Syntax:

operation ::= `hw.bitcast` $input attr-dict `:` functional-type($input, $result)

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Operands:

Results:

hw.constant (::circt::hw::ConstantOp)

Produce a constant value

The constant operation produces a constant value of standard integer type without a sign.

  %result = hw.constant 42 : t1

Traits: ConstantLike, FirstAttrDerivedResultType

Interfaces: NoSideEffect (MemoryEffectOpInterface), OpAsmOpInterface

Effects: MemoryEffects::Effect{}

Attributes:

Results:

hw.enum.constant (::circt::hw::EnumConstantOp)

Produce a constant enumeration value.

The enum.constant operation produces an enumeration value of the specified enum value attribute.

  %0 = hw.enum.constant A : !hw.enum<A, B, C>

Traits: ConstantLike

Interfaces: NoSideEffect (MemoryEffectOpInterface), OpAsmOpInterface

Effects: MemoryEffects::Effect{}

Attributes:

Results:

hw.globalRef (::circt::hw::GlobalRefOp)

A global reference to uniquely identify eachinstance of an operation

Syntax:

operation ::= `hw.globalRef` $sym_name $namepath attr-dict

This works like a symbol reference to an operation by specifying the instance path to uniquely identify it globally. It can be used to attach per instance metadata (non-local attributes). This also lets components of the path point to a common entity.

Traits: IsolatedFromAbove

Interfaces: Symbol, SymbolUserOpInterface

Attributes:

hw.generator.schema (::circt::hw::HWGeneratorSchemaOp)

HW Generator Schema declaration

Syntax:

operation ::= `hw.generator.schema` $sym_name `,` $descriptor `,` $requiredAttrs attr-dict

The “hw.generator.schema” operation declares a kind of generated module by declaring the schema of meta-data required. A generated module instance of a schema is independent of the external method of producing it. It is assumed that for well known schema instances, multiple external tools might exist which can process it. Generator nodes list attributes required by hw.module.generated instances.

For example: generator.schema @MEMORY, “Simple-Memory”, [“ports”, “write_latency”, “read_latency”] module.generated @mymem, @MEMORY(ports) -> (ports) {write_latency=1, read_latency=1, ports=[“read”,“write”]}

Traits: HasParent mlir::ModuleOp

Interfaces: Symbol

Attributes:

hw.module.extern (::circt::hw::HWModuleExternOp)

HW external Module

The “hw.module.extern” operation represents an external reference to a Verilog module, including a given name and a list of ports.

The ‘verilogName’ attribute (when present) specifies the spelling of the module name in Verilog we can use. TODO: This is a hack because we don’t have proper parameterization in the hw.dialect. We need a way to represent parameterized types instead of just concrete types.

Traits: HasParent mlir::ModuleOp

Interfaces: FunctionOpInterface, HWModuleLike, HWMutableModuleLike, OpAsmOpInterface, Symbol

Attributes:

hw.module.generated (::circt::hw::HWModuleGeneratedOp)

HW Generated Module

The “hw.module.generated” operation represents a reference to an external module that will be produced by some external process. This represents the name and list of ports to be generated.

The ‘verilogName’ attribute (when present) specifies the spelling of the module name in Verilog we can use. See hw.module for an explanation.

Traits: HasParent mlir::ModuleOp, IsolatedFromAbove

Interfaces: FunctionOpInterface, HWModuleLike, HWMutableModuleLike, OpAsmOpInterface, Symbol, SymbolUserOpInterface

Attributes:

hw.module (::circt::hw::HWModuleOp)

HW Module

The “hw.module” operation represents a Verilog module, including a given name, a list of ports, a list of parameters, and a body that represents the connections within the module.

Traits: HasParent mlir::ModuleOp, IsolatedFromAbove, SingleBlockImplicitTerminator

Interfaces: FunctionOpInterface, HWModuleLike, HWMutableModuleLike, OpAsmOpInterface, RegionKindInterface, Symbol

Attributes:

hw.instance (::circt::hw::InstanceOp)

Create an instance of a module

This represents an instance of a module. The inputs and results are the referenced module’s inputs and outputs. The argNames and resultNames attributes must match the referenced module.

Any parameters in the “old” format (slated to be removed) are stored in the oldParameters dictionary.

Interfaces: HWInstanceLike, OpAsmOpInterface, SymbolUserOpInterface

Attributes:

Operands:

Results:

hw.output (::circt::hw::OutputOp)

HW termination operation

Syntax:

operation ::= `hw.output` attr-dict ($outputs^ `:` qualified(type($outputs)))?

“hw.output” marks the end of a region in the HW dialect and the values to put on the output ports.

Traits: HasParent, ReturnLike, Terminator

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Operands:

hw.param.value (::circt::hw::ParamValueOp)

Return the value of a parameter expression as an SSA value that may be used
by other ops.

Syntax:

operation ::= `hw.param.value` custom<ParamValue>($value, qualified(type($result))) attr-dict

Traits: ConstantLike, FirstAttrDerivedResultType

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Attributes:

Results:

hw.probe (::circt::hw::ProbeOp)

Probe values for use in remote references

Syntax:

operation ::= `hw.probe` $inner_sym attr-dict (`,` $captured^ `:` qualified(type($captured)))?

Captures values without binding to any accidental name. This allows capturing names holding values of interest while allowing the name to resolved only at emission time.

Attributes:

Operands:

hw.struct_create (::circt::hw::StructCreateOp)

Create a struct from constituent parts.

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Operands:

Results:

hw.struct_explode (::circt::hw::StructExplodeOp)

Expand a struct into its constituent parts.

%result:2 = hw.struct_explode %input : !hw.struct<foo: i19, bar: i7>

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Operands:

Results:

hw.struct_extract (::circt::hw::StructExtractOp)

Extract a named field from a struct.

%result = hw.struct_extract %input["field"] : !hw.struct<field: type>

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Attributes:

Operands:

Results:

hw.struct_inject (::circt::hw::StructInjectOp)

Inject a value into a named field of a struct.

%result = hw.struct_inject %input["field"], %newValue
    : !hw.struct<field: type>

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Attributes:

Operands:

Results:

hw.type_scope (::circt::hw::TypeScopeOp)

Type declaration wrapper.

Syntax:

operation ::= `hw.type_scope` $sym_name $body attr-dict

An operation whose one body block contains type declarations. This op provides a scope for type declarations at the top level of an MLIR module. It is a symbol that may be looked up within the module, as well as a symbol table itself, so type declarations may be looked up.

Traits: NoRegionArguments, NoTerminator, SingleBlock, SymbolTable

Interfaces: Symbol

Attributes:

hw.typedecl (::circt::hw::TypedeclOp)

Type declaration.

Syntax:

operation ::= `hw.typedecl` $sym_name (`,` $verilogName^)? `:` $type attr-dict

Associate a symbolic name with a type. Traits: HasParent

Interfaces: Symbol

Attributes:

hw.union_create (::circt::hw::UnionCreateOp)

Create a union with the specified value.

Create a union with the value ‘input’, which can then be accessed via the specified field.

  %x = hw.constant 0 : i3
  %z = hw.union_create "bar", %x : !hw.union<bar: i3, baz: i8>

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Attributes:

Operands:

Results:

hw.union_extract (::circt::hw::UnionExtractOp)

Get a union member.

Get the value of a union, interpreting it as the type of the specified member field. Extracting a value belonging to a different field than the union was initially created will result in undefined behavior.

  %u = ...
  %v = hw.union_extract %u["foo"] : !hw.union<foo: i3, bar: i16>
  // %v is of type 'i3'

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Attributes:

Operands:

Results:

Attribute definition

EnumFieldAttr

Enumeration field attribute

This attribute represents a field of an enumeration.

Examples:

  #hw.enum.value<A, !hw.enum<A, B, C>>

Parameters:

FileListAttr

Ouput filelist attribute

Syntax:

!hw.output_filelist<
  ::mlir::StringAttr   # filename
>

This attribute represents an output filelist for something which will be printed. The filename string is the file which the filename of the operation to be output to.

When ExportVerilog runs, some of the files produced are lists of other files which are produced. Each filelist exported contains entities’ output file with FileListAttr marked.

Examples:

  #hw.ouput_filelist<"/home/tester/t.F">
  #hw.ouput_filelist<"t.f">

Parameters:

GlobalRefAttr

Refer to a non-local symbol

Syntax:

!hw.globalNameRef<
  ::mlir::FlatSymbolRefAttr   # glblSym
>

This works like a symbol reference, but to a global symbol with a possible unique instance path.

Parameters:

InnerRefAttr

Refer to a name inside a module

This works like a symbol reference, but to a name inside a module.

Parameters:

OutputFileAttr

Output file attribute

This attribute represents an output file for something which will be printed. The filename string is the file to be output to. If filename ends in a / it is considered an output directory.

When ExportVerilog runs, one of the files produced is a list of all other files which are produced. The flag excludeFromFileList controls if this file should be included in this list. If any OutputFileAttr referring to the same file sets this to true, it will be included in the file list. This option defaults to false.

For each file emitted by the verilog emitter, certain prelude output will be included before the main content. The flag includeReplicatedOps can be used to disable the addition of the prelude text. All OutputFileAttrs referring to the same file must use a consistent setting for this value. This option defaults to true.

Examples:

  #hw.ouput_file<"/home/tester/t.sv">
  #hw.ouput_file<"t.sv", excludeFromFileList, includeReplicatedOps>

Parameters:

ParamDeclAttr

Module or instance parameter definition

An attribute describing a module parameter, or instance parameter specification.

Parameters:

ParamDeclRefAttr

Is a reference to a parameter value.

Parameters:

ParamExprAttr

Parameter expression combining operands

Parameters:

ParamVerbatimAttr

Represents text to emit directly to SystemVerilog for a parameter

Parameters:

Type constraint definition

an ArrayType

a EnumType

an integer bitvector of one or more bits

a type without inout

a known primitive element

InOutType

a StructType

a UnionType

Type definition

ArrayType

fixed-sized array

Fixed sized HW arrays are roughly similar to C arrays. On the wire (vs. in a memory), arrays are always packed. Memory layout is not defined as it does not need to be since in silicon there is not implicit memory sharing.

Parameters:

EnumType

HW Enum type

Represents an enumeration of values. Enums are interpreted as integers with a synthesis-defined encoding. !hw.enum<field1, field2>

Parameters:

InOutType

inout type

InOut type is used for model operations and values that have “connection” semantics, instead of typical dataflow behavior. This is used for wires and inout ports in Verilog.

Parameters:

IntType

parameterized-width integer

Parameterized integer types are equivalent to the MLIR standard integer type: it is signless, and may be any width integer. This type represents the case when the width is a parameter in the HW dialect sense.

Parameters:

StructType

HW struct type

Represents a structure of name, value pairs. !hw.struct<fieldName1: Type1, fieldName2: Type2>

Parameters:

TypeAliasType

An symbolic reference to a type declaration

A TypeAlias is parameterized by a SymbolRefAttr, which points to a TypedeclOp. The root reference should refer to a TypeScope within the same outer ModuleOp, and the leaf reference should refer to a type within that TypeScope. A TypeAlias is further parameterized by the inner type, which is needed to be known at the time the type is parsed.

Upon construction, a TypeAlias stores the symbol reference and type, and canonicalizes the type to resolve any nested type aliases. The canonical type is also cached to avoid recomputing it when needed.

Parameters:

UnionType

An untagged union of types

Parameters:

UnpackedArrayType

SystemVerilog ‘unpacked’ fixed-sized array

Unpacked arrays are a more flexible array representation than packed arrays, and are typically used to model memories. See SystemVerilog Spec 7.4.2.

Parameters:

'hw' Dialect Docs

• HW Dialect Rationale