20. 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 each instruction that the target machine supports (or at least each instruction that 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 semicolon is inside a quoted string.

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

20.1 Overview of How the Machine Description is Used		How the machine description is used.
20.2 Everything about Instruction Patterns		How to write instruction patterns.
20.3 Example of define_insn		An explained example of a define_insn pattern.
20.4 RTL Template		The RTL template defines what insns match a pattern.
20.5 Output Templates and Operand Substitution		The output template says how to make assembler code from such an insn.
20.6 C Statements for Assembler Output		For more generality, write C code to output the assembler code.
20.7 Operand Constraints		When not all operands are general operands.
20.8 Standard Pattern Names For Generation		Names mark patterns to use for code generation.
20.9 When the Order of Patterns Matters		When the order of patterns makes a difference.
20.10 Interdependence of Patterns		Having one pattern may make you need another.
20.11 Defining Jump Instruction Patterns		Special considerations for patterns for jump insns.
20.12 Defining Looping Instruction Patterns		How to define patterns for special looping insns.
20.13 Canonicalization of Instructions
20.14 Defining RTL Sequences for Code Generation		Generating a sequence of several RTL insns for a standard operation.
20.15 Defining How to Split Instructions		Splitting Instructions into Multiple Instructions.
20.16 Machine-Specific Peephole Optimizers		Defining machine-specific peephole optimizations.
20.17 Instruction Attributes		Specifying the value of attributes for generated insns.
20.18 Conditional Execution		Generating define_insn patterns for predication.
20.19 Constant Definitions		Defining symbolic constants that can be used in the md file.