======================================== Machine IR (MIR) Format Reference Manual ======================================== .. contents:: :local: .. warning:: This is a work in progress. Introduction ============ This document is a reference manual for the Machine IR (MIR) serialization format. MIR is a human readable serialization format that is used to represent LLVM's :ref:`machine specific intermediate representation `. The MIR serialization format is designed to be used for testing the code generation passes in LLVM. Overview ======== The MIR serialization format uses a YAML container. YAML is a standard data serialization language, and the full YAML language spec can be read at `yaml.org `_. A MIR file is split up into a series of `YAML documents`_. The first document can contain an optional embedded LLVM IR module, and the rest of the documents contain the serialized machine functions. .. _YAML documents: http://www.yaml.org/spec/1.2/spec.html#id2800132 High Level Structure ==================== Embedded Module --------------- When the first YAML document contains a `YAML block literal string`_, the MIR parser will treat this string as an LLVM assembly language string that represents an embedded LLVM IR module. Here is an example of a YAML document that contains an LLVM module: .. code-block:: llvm --- | define i32 @inc(i32* %x) { entry: %0 = load i32, i32* %x %1 = add i32 %0, 1 store i32 %1, i32* %x ret i32 %1 } ... .. _YAML block literal string: http://www.yaml.org/spec/1.2/spec.html#id2795688 Machine Functions ----------------- The remaining YAML documents contain the machine functions. This is an example of such YAML document: .. code-block:: llvm --- name: inc tracksRegLiveness: true liveins: - { reg: '%rdi' } body: | bb.0.entry: liveins: %rdi %eax = MOV32rm %rdi, 1, _, 0, _ %eax = INC32r killed %eax, implicit-def dead %eflags MOV32mr killed %rdi, 1, _, 0, _, %eax RETQ %eax ... The document above consists of attributes that represent the various properties and data structures in a machine function. The attribute ``name`` is required, and its value should be identical to the name of a function that this machine function is based on. The attribute ``body`` is a `YAML block literal string`_. Its value represents the function's machine basic blocks and their machine instructions. Machine Instructions Format Reference ===================================== The machine basic blocks and their instructions are represented using a custom, human readable serialization language. This language is used in the `YAML block literal string`_ that corresponds to the machine function's body. A source string that uses this language contains a list of machine basic blocks, which are described in the section below. Machine Basic Blocks -------------------- A machine basic block is defined in a single block definition source construct that contains the block's ID. The example below defines two blocks that have an ID of zero and one: .. code-block:: llvm bb.0: bb.1: A machine basic block can also have a name. It should be specified after the ID in the block's definition: .. code-block:: llvm bb.0.entry: ; This block's name is "entry" The block's name should be identical to the name of the IR block that this machine block is based on. Block References ^^^^^^^^^^^^^^^^ The machine basic blocks are identified by their ID numbers. Individual blocks are referenced using the following syntax: .. code-block:: llvm %bb.[.] Examples: .. code-block:: llvm %bb.0 %bb.1.then Successors ^^^^^^^^^^ The machine basic block's successors have to be specified before any of the instructions: .. code-block:: llvm bb.0.entry: successors: %bb.1.then, %bb.2.else bb.1.then: bb.2.else: The branch weights can be specified in brackets after the successor blocks. The example below defines a block that has two successors with branch weights of 32 and 16: .. code-block:: llvm bb.0.entry: successors: %bb.1.then(32), %bb.2.else(16) Live In Registers ^^^^^^^^^^^^^^^^^ The machine basic block's live in registers have to be specified before any of the instructions: .. code-block:: llvm bb.0.entry: liveins: %edi, %esi The list of live in registers and successors can be empty. The language also allows multiple live in register and successor lists - they are combined into one list by the parser. Miscellaneous Attributes ^^^^^^^^^^^^^^^^^^^^^^^^ The attributes ``IsAddressTaken``, ``IsLandingPad`` and ``Alignment`` can be specified in brackets after the block's definition: .. code-block:: llvm bb.0.entry (address-taken): bb.2.else (align 4): bb.3(landing-pad, align 4): .. TODO: Describe the way the reference to an unnamed LLVM IR block can be preserved. Machine Instructions -------------------- A machine instruction is composed of a name, machine operands, :ref:`instruction flags `, and machine memory operands. The instruction's name is usually specified before the operands. The example below shows an instance of the X86 ``RETQ`` instruction with a single machine operand: .. code-block:: llvm RETQ %eax However, if the machine instruction has one or more explicitly defined register operands, the instruction's name has to be specified after them. The example below shows an instance of the AArch64 ``LDPXpost`` instruction with three defined register operands: .. code-block:: llvm %sp, %fp, %lr = LDPXpost %sp, 2 The instruction names are serialized using the exact definitions from the target's ``*InstrInfo.td`` files, and they are case sensitive. This means that similar instruction names like ``TSTri`` and ``tSTRi`` represent different machine instructions. .. _instruction-flags: Instruction Flags ^^^^^^^^^^^^^^^^^ The flag ``frame-setup`` can be specified before the instruction's name: .. code-block:: llvm %fp = frame-setup ADDXri %sp, 0, 0 .. TODO: Describe the parsers default behaviour when optional YAML attributes are missing. .. TODO: Describe the syntax for the bundled instructions. .. TODO: Describe the syntax of the immediate machine operands. .. TODO: Describe the syntax of the register machine operands. .. TODO: Describe the syntax of the virtual register operands and their YAML definitions. .. TODO: Describe the syntax of the register operand flags and the subregisters. .. TODO: Describe the machine function's YAML flag attributes. .. TODO: Describe the syntax for the global value, external symbol and register mask machine operands. .. TODO: Describe the frame information YAML mapping. .. TODO: Describe the syntax of the stack object machine operands and their YAML definitions. .. TODO: Describe the syntax of the constant pool machine operands and their YAML definitions. .. TODO: Describe the syntax of the jump table machine operands and their YAML definitions. .. TODO: Describe the syntax of the block address machine operands. .. TODO: Describe the syntax of the CFI index machine operands. .. TODO: Describe the syntax of the metadata machine operands, and the instructions debug location attribute. .. TODO: Describe the syntax of the target index machine operands. .. TODO: Describe the syntax of the register live out machine operands. .. TODO: Describe the syntax of the machine memory operands.