Telescoping Languages:

A Compiler Strategy for Implementation of High-Level

Domain-Specific Programming Systems

Ken KennedyRice University

Motivation

•Background—Increasing Complexity of Computer Architectures

and Application Structures

—Difficulty of high-performance programming

—Need to allow end-user to develop applications

—Use scripting languages like MATLAB, VisualBasic

•Problems—Performance limited : Interpreted

—Treats Libraries as black boxes

—Rewrite in C/C++/FORTRAN for “production” work

Solution 1:Translate to Low-level

•DeRose/Padua, Int. Conf. Supercomputing,1996

•Use global optimization on low-level code

component library

component library

user libraryuser library

scriptscript

intermediate code

intermediate codetranslatortranslator

global optimizerglobal

optimizer

code generator

code generator

Solution 1:Translate to Low-level

•Problems:—Potentially high compilation times,

even for simple scripts

—Expert knowledge about libraries lost

component library

component library

user libraryuser library

scriptscript

intermediate code

intermediate codetranslatortranslator

global optimizerglobal

optimizer

code generator

code generator

Telescoping Languages

• The Goals—Perform fast local optimization within scripts

—Generate efficient code from script quickly

• The Solution—Extensively pre-compile and optimize library

implementations

—Maintain database of precompiled libraries

—Use language building compiler to produce enhanced script compiler that supports library calls as language primitives

—Can be done in iterations

Domain Library

Domain Library

Language-Building Compiler

Language-Building Compiler

Script Translator

Script Translator

Enhanced-Language Compiler

Enhanced-Language Compiler

User ScriptUser ScriptOptimized

Object Program

Optimized Object

Program

AnnotationsAnnotations

could run for hours

understands library calls as primitives

Telescoping Languages

AnnotationsAnnotationsLanguage-Building Compiler

Language-Building Compiler

Domain Library

Domain Library

Language-Building Compiler

Language-Building Compiler

Script Translator

Script Translator

Enhanced-Language Compiler

Enhanced-Language Compiler

User ScriptUser ScriptOptimized

Object Program

Optimized Object

Program

AnnotationsAnnotations

Telescoping Languages

•Construction of Jump Functions—Summarize the value of output parameters for a

particular procedure in terms of its inputs

—Allows instant propagation of parameter properties (type and value) through procedure calls at script compilation time

—Library compilation computes Jump Functions for every public interface

—Helps inter-procedural analysis

—Compositions of JFs need to account for special versions of procedures

Optimization Strategies

Construction of Jump Functions : Example

PROGRAM MAIN V =1 N =0DO WHILE(V>0) V = FUNC(V) N =N +1ENDDOPRINT NEND MAIN

REAL FUNCTION FUNC(X) ! Part of library

IF (X>0) THEN RETURN (X-1)ELSE RETURN XENDIFEND FUNC

! X known > 0inline(X-1)

! X known <= 0inline(X)

! X unknowninline( (X>0 ? X-1 : X) )

PROGRAM MAIN V =1 N =0! DO eliminated V =V -1 N =N +1! ENDDO eliminatedPRINT NEND MAIN

PROGRAM MAIN PRINT 1END MAIN

Optimization Strategies

•Reverse Program Analysis —Identify points of profitable optimization within

procedure

—Propagate information backward to procedure interface

—Can work across inter-library interfaces

•Recognition and exploitation of identities—Specify when it is safe to replace composite library

calls with efficient specialized code at script compilation time

—Example: Replacing a PUSH followed immediately by a POP for calls to a stack library

Implementation

•Steps in Script Compilation—Calculate Jump Functions

—Analyze propagation of variable properties

(value and type)

—At each invocation point for libraries, select most specialized code given the variable properties

—Substitute the selected code inline

•Discussion : Loss of portability?•Supporting performance portability

—Compute specialized implementations, along with jump functions for each public interface

—Specialize the code for each target machine

Advantages

•Reliability—Script compiler can validate parameters

—Libraries can specify correctness conditions

•Client-Server communications—Optimize application along with interface specific

part of code

—Perform strength reductions for remote calls

•Protection of Source Code—Allows library developer to prohibit inlining of

specific portions of code

Discussions

•Dealing with variation in application data structures—Solution: Trade code space for configurability?

—Select from alternative implementations at run time

•Scope for more optimizations—Further work : Chauhan & Kennedy, “Optimizing

Strategies for Telescoping Languages: Procedure Strength Reduction and Procedure Vectorization”, Proceedings of the 15th ACM International Conference on Supercomputing, June 16-21, 2001

•Comparison with alternative approaches

Thank You