Automating Fortran - C Interoperability - PowerPoint Presentation

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Automating Fortran - C Interoperability

Prepared by: Sisi Liu (Garnet)Mentor: Dan NagleCo-Mentor: Davide del Vento

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Background: Fortran-C Interoperability

Scientific programs supported by the large systems at NCAR are often written in a combination of Fortran and CFortran modules connect C

library functions to the Fortran

program with Fortran compiler’s support

Currently, modules are written manually to express C interfaces. In other words, the translation from C to Fortran is done by hand.

2Slide3

Background: Fortran-C Interoperability

3Slide4

Introduction: Automating Fortran Project

What is the object of this project?Build a source to source translation toolTranslate C headers to Fortran modules to let Fortran programs use C library functions

Why such tool is needed?

Automated module generation helps

avoid redundant work and error-prone manual laboringEasy for maintenance and update

4Slide5

Introduction: Automating Fortran Project

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Approaches: Finding the Right Tool

ANTLR

Lexer

and p

arser tool

– manually write the parser, last

resort

GCC

GENERIC – complicated and hard to modify

GIMPLE – unused

variables are optimized (nearly the entire

header is removed in the output)

ROSE Compiler

Intermediate representation

and support both C and Fortran

lack of public

APIsClang LLVMClang AST – modular design, abundant APIs

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Abstract Syntax Tree (AST)

A tree representation of the abstract syntactic structure of codewidely used in compilers as intermediate representation

Language-independent

A Simple Abstract

Syntax Tree

Example, tokens of the source code become tree nodes.

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Steps to Automate

Source-to-Source TranslationLexical analysis and parse C to AST

Traversing through each node of AST recursively

Identify the node: cast to specific declaration, type or expression

Tree structure. May expand to more nodes. (e.g.

FunctionDecl

expands to return type and multiple

VarDecl

)

Create a object for each node with all needed info for translation

Unparse

the content of each node to Fortran code by calling the “

formatASString

()” method of this object to dump the Fortran code

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Source-to-Source Translation Workflow

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Implementation—Using Clang Tool to Traverse AST

Clang AST

Node

Structure Overview

Declaration

FunctionDecl

—declares functions, might contain a function body

VarDecl

—declares values or types to variables

RecordDecl

—declares

struct

or union

EnumDecl

—declares enumerations

TypeDefDecl

—defines a type to variablesStatement (function body, unlikely to be seen in headers)Type (inside declaration)Iso_c_binding—convert intrinsic C types to Fortran typesType defined identifiersTypes can be more complicated10Slide11

The source code can expand to very long abstract syntax tree!

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Implementation—Declarations

Function Declaration

Expand to

r

eturn and argument type

Support

intrinsic

types: all literal type,

c

ptr

and

funptr

, and type defined identifiers

Function body is preserved as comment

Unnamed arguments are automatically named as arg_1, arg_2

…

Add import attribute to import derived types12Slide13

Implementation—Declarations

Record Declaration (

struct

)

and

Typedef

Declaration

Translate as derived types in Fortran

Identifier is required in Fortran but not in C

Anonymous

struct

will be preserved as comment

Enumeration

Declaration

Directly translate to Fortran

Enumeration

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Implementation— Variable Declarations

VarDecl without an init valueSupport all intrinsic and declared types

Names that are valid in C (“_id”) but not in Fortran are commented out

VarDecl

with an init value

Support literal type, pointers, string and multidimensional array

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Implementation—Macros are Different

Macros are not part of AST but preprocessorPreprocessor functions only return the macro kind (object or function) and the source textUnlike dealing with object-oriented AST, values

or types have to be manually

parsed

Limited types (only intrinsic types) are supported

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Implementation—Macros

Object MacroLiteral value declaration (e.g.

#define INT_VARIABLE 128

)->variable

declarationAlias type declaration (e.g.

#define long unsigned long

int

)->derived

type

Identifier declaration

(e.g.

#define

id1 id2

) -> no type information, so commented out

Function Macro (e.g.

#define SQUARE(x) (x*x)

)Lack of argument and return types (assume to be integer) ->function declaration16Slide17

Example:

PTHREAD_CANCELED is commented out due to the value’s type is non-trivial

PTHREAD_MUTEX_DEFAULT is commented out because there is no type information for this declaration

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Overall Performance

About 40% of the system headers in the /usr/include can be correctly compiledAnother 40% headers contain unavoidable compilation errors (minor errors that need to be manually modified)

Same module (file name) and function name, not allowed in Fortran but allowed in C

Some symbols are valid in C but not in Fortran (e.g. ‘_id’ and ‘id-1’)

Type defined (tag named

)

struct

with an identifier will be declared twice due to they are 2 separate nodes in AST

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Future Work

Potential improvements for the rest 20% headersNon-intrinsic undeclared types cannot be recognized such as unrecognized_type

(void (

Tcl_Time

*,

ClientData

)

No

suitable auto

translation for Union in

Fortran

Remove the redundant

struct

that is defined twice

Out of source types that are defined other files can cause

u

ndeclared variables errors19Slide20

Brief Demo

20

Shell

script of using the tool to generate

pthread

module

A mini

Fortran hello world

program that uses Fortran

pthread

module Slide21

Acknowledgement

Many thanks to:Mentors: Dan Nagle and Davide Del Vento

NCAR and

SIParCS

staff

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References

H2m tool repository:https://github.com/garnetliu/llvm-clang-autoFortranTool

Building instruction:

https

://

github.com/garnetliu/llvm-clang-autoFortranTool/blob/master/Tool%20Building%20Instruction.pdf

Figure reference:

Performing

Source-to-Source Transformations with Clang by Olaf

Krzikalla

http://llvm.org/devmtg/2013-04/krzikalla-slides.pdf

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