Welcome to Flang’s documentation

Flang is LLVM’s Fortran frontend that can be found here. It is often referred to as “LLVM Flang” to differentiate itself from “Classic Flang” - these are two separate and independent Fortran compilers. LLVM Flang is under active development. While it is capable of generating executables for a number of examples, some functionality is still missing. See Getting Involved for tips on how to get in touch with us and to learn more about the current status.

• Flang |version| (In-Progress) Release Notes

Contributing to Flang

• C++14/17 features used in f18
• Flang C++ Style Guide
• Design Guideline
• Fortran For C Programmers
• Getting Involved
• Getting Started
• How to implement a Sematic Check in Flang
• Pull request checklist

Design Documents

• Aliasing in Fortran
• Aliasing analysis in FIR
• Array Composition
• Assumed-Rank Objects
• Bijective Internal Name Uniquing
• Representation of Fortran function calls
• Implementation of CHARACTER types in f18
• Complex Operations
• Control Flow Graph
• Debug Generation
• Testing
• Resources
• Compiler directives supported by Flang
• Directive Details
• DO CONCURRENT isn’t necessarily concurrent
• Fortran Extensions supported by Flang
• A first take on Fortran 202X features for LLVM Flang
• Design: FIR Array operations
• FIR Language Reference
• Flang command line argument reference
• Flang drivers
• A Fortran feature history cheat sheet
• Design: Fortran IR
• Fortran Tests in the LLVM Test Suite
• High-Level Fortran IR (HLFIR)
• Fortran I/O Runtime Library Internal Design
• Trampolines for pointers to internal procedures.
• A categorization of standard (2018) and extended Fortran intrinsic procedures
• Implementation of Intrinsic types in f18
• Semantics: Resolving Labels and Construct Names
• Module Files
• OpenACC in Flang
• OpenACC dialect: Fortran descriptor management in the offload data environment
• OpenMP 4.5 Grammar
• Introduction to Declare Target
• Declare Target as represented in the OpenMP Dialect
• Declare Target Fortran OpenMP Lowering
• Declare Target Transformation Passes for Flang
• Declare Target OpenMP Dialect To LLVM-IR Lowering
• Current Support
• OpenMP dialect: Fortran descriptor type mapping for offload
• OpenMP dialect differences from OpenACC dialect
• OpenMP Semantic Analysis
• Compiler options comparison
• Overview of Compiler Phases
• Parameterized Derived Types (PDTs)
• Parser Combinators
• The F18 Parser
• Polymorphic Entities
• Fortran Preprocessing
• Procedure Pointer
• Runtime Descriptors
• Environment variables of significance to Fortran execution
• The derived type runtime information table
• Semantic Analysis
• Fortran 2018 Grammar
• Stack arrays pass
• Flang support for REAL(16) math intrinsics

Indices and tables

• Index

• Search Page