GNU Compiler Collection (GCC) Internals

This file documents the internals of the GNU compilers.

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(a) The FSF's Front-Cover Text is:

A GNU Manual

(b) The FSF's Back-Cover Text is:

You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.

Short Contents

Introduction 1 Contributing to GCC Development 2 GCC and Portability 3 Interfacing to GCC Output 4 The GCC low-level runtime library 4.1 Routines for integer arithmetic 4.1.1 Arithmetic functions 4.1.2 Comparison functions 4.1.3 Trapping arithmetic functions 4.1.4 Bit operations

4.2 Routines for floating point emulation

4.2.1 Arithmetic functions 4.2.2 Conversion functions 4.2.3 Comparison functions

4.3 Language-independent routines for exception handling

4.4 Miscellaneous runtime library routines

4.4.1 Cache control functions

5 Language Front Ends in GCC

6 Source Tree Structure and Build System

6.1 Configure Terms and History 6.2 Top Level Source Directory 6.3 The gcc Subdirectory 6.3.1 Subdirectories of gcc 6.3.2 Configuration in the gcc Directory 6.3.2.1 Scripts Used by configure 6.3.2.2 The config.build; config.host; and config.gcc Files 6.3.2.3 Files Created by configure

6.3.3 Build System in the gcc Directory

6.3.4 Makefile Targets

6.3.5 Library Source Files and Headers under the gcc Directory

6.3.6 Headers Installed by GCC

6.3.7 Building Documentation

6.3.7.1 Texinfo Manuals 6.3.7.2 Man Page Generation 6.3.7.3 Miscellaneous Documentation

6.3.8 Anatomy of a Language Front End

6.3.8.1 The Front End language Directory 6.3.8.2 The Front End config-lang.in File

6.3.9 Anatomy of a Target Back End

6.4 Testsuites

6.4.1 Idioms Used in Testsuite Code 6.4.2 Directives used within DejaGnu tests 6.4.3 Ada Language Testsuites 6.4.4 C Language Testsuites 6.4.5 The Java library testsuites. 6.4.6 Support for testing gcov 6.4.7 Support for testing profile-directed optimizations 6.4.8 Support for testing binary compatibility

7 Passes and Files of the Compiler

7.1 Parsing pass 7.2 Gimplification pass 7.3 Pass manager 7.4 Tree-SSA passes 7.5 RTL passes

8 Trees: The intermediate representation used by the C and C++ front ends

8.1 Deficiencies 8.2 Overview 8.2.1 Trees 8.2.2 Identifiers 8.2.3 Containers

8.3 Types

8.4 Scopes

8.4.1 Namespaces 8.4.2 Classes

8.5 Declarations

8.6 Functions

8.6.1 Function Basics 8.6.2 Function Bodies 8.6.2.1 Statements

8.7 Attributes in trees

8.8 Expressions

9 Analysis and Optimization of GIMPLE Trees

9.1 GENERIC 9.2 GIMPLE 9.2.1 Interfaces 9.2.2 Temporaries 9.2.3 Expressions 9.2.3.1 Compound Expressions 9.2.3.2 Compound Lvalues 9.2.3.3 Conditional Expressions 9.2.3.4 Logical Operators

9.2.4 Statements

9.2.4.1 Blocks 9.2.4.2 Statement Sequences 9.2.4.3 Empty Statements 9.2.4.4 Loops 9.2.4.5 Selection Statements 9.2.4.6 Jumps 9.2.4.7 Cleanups 9.2.4.8 Exception Handling

9.2.5 GIMPLE Example

9.2.6 Rough GIMPLE Grammar

9.3 Annotations

9.4 Statement Operands

9.4.1 Operand Iterators

9.5 Static Single Assignment

9.5.1 Preserving the SSA form 9.5.2 Examining SSA_NAME nodes 9.5.3 Walking use-def chains 9.5.4 Walking the dominator tree

9.6 Alias analysis

10 RTL Representation

10.1 RTL Object Types 10.2 RTL Classes and Formats 10.3 Access to Operands 10.4 Access to Special Operands 10.5 Flags in an RTL Expression 10.6 Machine Modes 10.7 Constant Expression Types 10.8 Registers and Memory 10.9 RTL Expressions for Arithmetic 10.10 Comparison Operations 10.11 Bit-Fields 10.12 Vector Operations 10.13 Conversions 10.14 Declarations 10.15 Side Effect Expressions 10.16 Embedded Side-Effects on Addresses 10.17 Assembler Instructions as Expressions 10.18 Insns 10.19 RTL Representation of Function-Call Insns 10.20 Structure Sharing Assumptions 10.21 Reading RTL

11 Control Flow Graph

11.1 Basic Blocks 11.2 Edges 11.3 Profile information 11.4 Maintaining the CFG 11.5 Liveness information

12 Machine Descriptions

12.1 Overview of How the Machine Description is Used 12.2 Everything about Instruction Patterns 12.3 Example of define_insn 12.4 RTL Template 12.5 Output Templates and Operand Substitution 12.6 C Statements for Assembler Output 12.7 Predicates 12.7.1 Machine-Independent Predicates 12.7.2 Defining Machine-Specific Predicates

12.8 Operand Constraints

12.8.1 Simple Constraints 12.8.2 Multiple Alternative Constraints 12.8.3 Register Class Preferences 12.8.4 Constraint Modifier Characters 12.8.5 Constraints for Particular Machines

12.9 Standard Pattern Names For Generation

12.10 When the Order of Patterns Matters

12.11 Interdependence of Patterns

12.12 Defining Jump Instruction Patterns

12.13 Defining Looping Instruction Patterns

12.14 Canonicalization of Instructions

12.15 Defining RTL Sequences for Code Generation

12.16 Defining How to Split Instructions

12.17 Including Patterns in Machine Descriptions.

12.17.1 RTL Generation Tool Options for Directory Search

12.18 Machine-Specific Peephole Optimizers

12.18.1 RTL to Text Peephole Optimizers 12.18.2 RTL to RTL Peephole Optimizers

12.19 Instruction Attributes

12.19.1 Defining Attributes and their Values 12.19.2 Attribute Expressions 12.19.3 Assigning Attribute Values to Insns 12.19.4 Example of Attribute Specifications 12.19.5 Computing the Length of an Insn 12.19.6 Constant Attributes 12.19.7 Delay Slot Scheduling 12.19.8 Specifying processor pipeline description

12.20 Conditional Execution

12.21 Constant Definitions

12.22 Macros

12.22.1 Mode Macros 12.22.1.1 Defining Mode Macros 12.22.1.2 String Substitution in Mode Macros 12.22.1.3 Mode Macro Examples

12.22.2 Code Macros

13 Target Description Macros and Functions

13.1 The Global targetm Variable 13.2 Controlling the Compilation Driver, gcc 13.3 Run-time Target Specification 13.4 Defining data structures for per-function information. 13.5 Storage Layout 13.6 Layout of Source Language Data Types 13.7 Register Usage 13.7.1 Basic Characteristics of Registers 13.7.2 Order of Allocation of Registers 13.7.3 How Values Fit in Registers 13.7.4 Handling Leaf Functions 13.7.5 Registers That Form a Stack

13.8 Register Classes

13.9 Stack Layout and Calling Conventions

13.9.1 Basic Stack Layout 13.9.2 Exception Handling Support 13.9.3 Specifying How Stack Checking is Done 13.9.4 Registers That Address the Stack Frame 13.9.5 Eliminating Frame Pointer and Arg Pointer 13.9.6 Passing Function Arguments on the Stack 13.9.7 Passing Arguments in Registers 13.9.8 How Scalar Function Values Are Returned 13.9.9 How Large Values Are Returned 13.9.10 Caller-Saves Register Allocation 13.9.11 Function Entry and Exit 13.9.12 Generating Code for Profiling 13.9.13 Permitting tail calls

13.10 Implementing the Varargs Macros

13.11 Trampolines for Nested Functions

13.12 Implicit Calls to Library Routines

13.13 Addressing Modes

13.14 Condition Code Status

13.15 Describing Relative Costs of Operations

13.16 Adjusting the Instruction Scheduler

13.17 Dividing the Output into Sections (Texts, Data, ...)

13.18 Position Independent Code

13.19 Defining the Output Assembler Language

13.19.1 The Overall Framework of an Assembler File 13.19.2 Output of Data 13.19.3 Output of Uninitialized Variables 13.19.4 Output and Generation of Labels 13.19.5 How Initialization Functions Are Handled 13.19.6 Macros Controlling Initialization Routines 13.19.7 Output of Assembler Instructions 13.19.8 Output of Dispatch Tables 13.19.9 Assembler Commands for Exception Regions 13.19.10 Assembler Commands for Alignment

13.20 Controlling Debugging Information Format

13.20.1 Macros Affecting All Debugging Formats 13.20.2 Specific Options for DBX Output 13.20.3 Open-Ended Hooks for DBX Format 13.20.4 File Names in DBX Format 13.20.5 Macros for SDB and DWARF Output 13.20.6 Macros for VMS Debug Format

13.21 Cross Compilation and Floating Point

13.22 Mode Switching Instructions

13.23 Defining target-specific uses of attribute

13.24 Defining coprocessor specifics for MIPS targets.

13.25 Parameters for Precompiled Header Validity Checking

13.26 C++ ABI parameters

13.27 Miscellaneous Parameters

14 Host Configuration

14.1 Host Common 14.2 Host Filesystem 14.3 Host Misc

15 Makefile Fragments

15.1 Target Makefile Fragments 15.2 Host Makefile Fragments

16 collect2

17 Standard Header File Directories

18 Memory Management and Type Information

18.1 The Inside of a GTY(()) 18.2 Marking Roots for the Garbage Collector 18.3 Source Files Containing Type Information

Funding Free Software

The GNU Project and GNU/Linux

GNU GENERAL PUBLIC LICENSE

Preamble How to Apply These Terms to Your New Programs

GNU Free Documentation License

ADDENDUM: How to use this License for your documents

Contributors to GCC

Option Index

Concept Index

Next: Contributing, Up: (DIR)

Introduction

This manual documents the internals of the GNU compilers, including how to port them to new targets and some information about how to write front ends for new languages. It corresponds to GCC version 4.0.1. The use of the GNU compilers is documented in a separate manual. See Introduction.

This manual is mainly a reference manual rather than a tutorial. It discusses how to contribute to GCC (see Contributing), the characteristics of the machines supported by GCC as hosts and targets (see Portability), how GCC relates to the ABIs on such systems (see Interface), and the characteristics of the languages for which GCC front ends are written (see Languages). It then describes the GCC source tree structure and build system, some of the interfaces to GCC front ends, and how support for a target system is implemented in GCC.

Additional tutorial information is linked to from http://gcc.gnu.org/readings.html.

GNU Compiler Collection (GCC) Internals

Short Contents

Table of Contents

Introduction