GNU Info

(gcc-295.info)Machine Desc

---

Next: Target Macros Prev: RTL Up: Top

---

Enter node , (file) or (file)node

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.

Patterns

How to write instruction patterns.

Example

An explained example of a `define_insn' pattern.

RTL Template

The RTL template defines what insns match a pattern.

Output Template

The output template says how to make assembler code

from such an insn.

Output Statement

For more generality, write C code to output

the assembler code.

Constraints

When not all operands are general operands.

Standard Names

Names mark patterns to use for code generation.

Pattern Ordering

When the order of patterns makes a difference.

Dependent Patterns

Having one pattern may make you need another.

Jump Patterns

Special considerations for patterns for jump insns.

Insn Canonicalizations

Canonicalization of Instructions

Peephole Definitions

Defining machine-specific peephole optimizations.

Expander Definitions

Generating a sequence of several RTL insns

for a standard operation.

Insn Splitting

Splitting Instructions into Multiple Instructions

Insn Attributes

Specifying the value of attributes for generated insns.