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16 Machine Descriptions ¶

A machine description has two parts: a file of instruction patterns(.md file) and a C header file of macro definitions.

The.md file for a target machine contains a pattern for eachinstruction that the target machine supports (or at least each instructionthat is worth telling the compiler about). It may also contain comments.A semicolon causes the rest of the line to be a comment, unless the semicolonis inside a quoted string.

See the next chapter for information on the C header file.

• Overview of How the Machine Description is Used
• Everything about Instruction Patterns
• Example ofdefine_insn
• RTL Template
• Output Templates and Operand Substitution
• C Statements for Assembler Output
• Compact Syntax
• Predicates
• Operand Constraints
• Standard Pattern Names For Generation
• When the Order of Patterns Matters
• Interdependence of Patterns
• Defining Jump Instruction Patterns
• Defining Looping Instruction Patterns
• Canonicalization of Instructions
• Defining RTL Sequences for Code Generation
• Defining How to Split Instructions
• Including Patterns in Machine Descriptions.
• Machine-Specific Peephole Optimizers
• Instruction Attributes
• Conditional Execution
• RTL Templates Transformations
• Constant Definitions
• Iterators