A Compilation Framework for Lifelong Program Analysis & Transformation
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The LLVM Instruction Set and Compilation Strategy
The LLVM Instruction Set and Compilation Strategy Chris Lattner Vikram Adve University of Illinois at Urbana-Champaign lattner,vadve ¡ @cs.uiuc.edu Abstract This document introduces the LLVM compiler infrastructure and instruction set, a simple approach that enables sophisticated code transformations at link time, runtime, and in the field. It is a pragmatic approach to compilation, interfering with programmers and tools as little as possible, while still retaining extensive high-level information from source-level compilers for later stages of an application’s lifetime. We describe the LLVM instruction set, the design of the LLVM system, and some of its key components. 1 Introduction Modern programming languages and software practices aim to support more reliable, flexible, and powerful software applications, increase programmer productivity, and provide higher level semantic information to the compiler. Un- fortunately, traditional approaches to compilation either fail to extract sufficient performance from the program (by not using interprocedural analysis or profile information) or interfere with the build process substantially (by requiring build scripts to be modified for either profiling or interprocedural optimization). Furthermore, they do not support optimization either at runtime or after an application has been installed at an end-user’s site, when the most relevant information about actual usage patterns would be available. The LLVM Compilation Strategy is designed to enable effective multi-stage optimization (at compile-time, link-time, runtime, and offline) and more effective profile-driven optimization, and to do so without changes to the traditional build process or programmer intervention. LLVM (Low Level Virtual Machine) is a compilation strategy that uses a low-level virtual instruction set with rich type information as a common code representation for all phases of compilation. -
What Is LLVM? and a Status Update
What is LLVM? And a Status Update. Approved for public release Hal Finkel Leadership Computing Facility Argonne National Laboratory Clang, LLVM, etc. ✔ LLVM is a liberally-licensed(*) infrastructure for creating compilers, other toolchain components, and JIT compilation engines. ✔ Clang is a modern C++ frontend for LLVM ✔ LLVM and Clang will play significant roles in exascale computing systems! (*) Now under the Apache 2 license with the LLVM Exception LLVM/Clang is both a research platform and a production-quality compiler. 2 A role in exascale? Current/Future HPC vendors are already involved (plus many others)... Apple + Google Intel (Many millions invested annually) + many others (Qualcomm, Sony, Microsoft, Facebook, Ericcson, etc.) ARM LLVM IBM Cray NVIDIA (and PGI) Academia, Labs, etc. AMD 3 What is LLVM: LLVM is a multi-architecture infrastructure for constructing compilers and other toolchain components. LLVM is not a “low-level virtual machine”! LLVM IR Architecture-independent simplification Architecture-aware optimization (e.g. vectorization) Assembly printing, binary generation, or JIT execution Backends (Type legalization, instruction selection, register allocation, etc.) 4 What is Clang: LLVM IR Clang is a C++ frontend for LLVM... Code generation Parsing and C++ Source semantic analysis (C++14, C11, etc.) Static analysis ● For basic compilation, Clang works just like gcc – using clang instead of gcc, or clang++ instead of g++, in your makefile will likely “just work.” ● Clang has a scalable LTO, check out: https://clang.llvm.org/docs/ThinLTO.html 5 The core LLVM compiler-infrastructure components are one of the subprojects in the LLVM project. These components are also referred to as “LLVM.” 6 What About Flang? ● Started as a collaboration between DOE and NVIDIA/PGI. -
CUDA Flux: a Lightweight Instruction Profiler for CUDA Applications
CUDA Flux: A Lightweight Instruction Profiler for CUDA Applications Lorenz Braun Holger Froning¨ Institute of Computer Engineering Institute of Computer Engineering Heidelberg University Heidelberg University Heidelberg, Germany Heidelberg, Germany [email protected] [email protected] Abstract—GPUs are powerful, massively parallel processors, hardware, it lacks verbosity when it comes to analyzing the which require a vast amount of thread parallelism to keep their different types of instructions executed. This problem is aggra- thousands of execution units busy, and to tolerate latency when vated by the recently frequent introduction of new instructions, accessing its high-throughput memory system. Understanding the behavior of massively threaded GPU programs can be for instance floating point operations with reduced precision difficult, even though recent GPUs provide an abundance of or special function operations including Tensor Cores for ma- hardware performance counters, which collect statistics about chine learning. Similarly, information on the use of vectorized certain events. Profiling tools that assist the user in such analysis operations is often lost. Characterizing workloads on PTX for their GPUs, like NVIDIA’s nvprof and cupti, are state-of- level is desirable as PTX allows us to determine the exact types the-art. However, instrumentation based on reading hardware performance counters can be slow, in particular when the number of the instructions a kernel executes. On the contrary, nvprof of metrics is large. Furthermore, the results can be inaccurate as metrics are based on a lower-level representation called SASS. instructions are grouped to match the available set of hardware Still, even if there was an exact mapping, some information on counters. -
Analysis of Program Optimization Possibilities and Further Development
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Theoretical Computer Science 90 (1991) 17-36 17 Elsevier Analysis of program optimization possibilities and further development I.V. Pottosin Institute of Informatics Systems, Siberian Division of the USSR Acad. Sci., 630090 Novosibirsk, USSR 1. Introduction Program optimization has appeared in the framework of program compilation and includes special techniques and methods used in compiler construction to obtain a rather efficient object code. These techniques and methods constituted in the past and constitute now an essential part of the so called optimizing compilers whose goal is to produce an object code in run time, saving such computer resources as CPU time and memory. For contemporary supercomputers, the requirement of the proper use of hardware peculiarities is added. In our opinion, the existence of a sufficiently large number of optimizing compilers with real possibilities of producing “good” object code has evidently proved to be practically significant for program optimization. The methods and approaches that have accumulated in program optimization research seem to be no lesser valuable, since they may be successfully used in the general techniques of program construc- tion, i.e. in program synthesis, program transformation and at different steps of program development. At the same time, there has been criticism on program optimization and even doubts about its necessity. On the one hand, this viewpoint is based on blind faith in the new possibilities bf computers which will be so powerful that any necessity to worry about program efficiency will disappear. -
Implementing Continuation Based Language in LLVM and Clang
Implementing Continuation based language in LLVM and Clang Kaito TOKUMORI Shinji KONO University of the Ryukyus University of the Ryukyus Email: [email protected] Email: [email protected] Abstract—The programming paradigm which use data seg- 1 __code f(Allocate allocate){ 2 allocate.size = 0; ments and code segments are proposed. This paradigm uses 3 goto g(allocate); Continuation based C (CbC), which a slight modified C language. 4 } 5 Code segments are units of calculation and Data segments are 6 // data segment definition sets of typed data. We use these segments as units of computation 7 // (generated automatically) 8 union Data { and meta computation. In this paper we show the implementation 9 struct Allocate { of CbC on LLVM and Clang 3.7. 10 long size; 11 } allocate; 12 }; I. A PRACTICAL CONTINUATION BASED LANGUAGE TABLE I The proposed units of programming are named code seg- CBCEXAMPLE ments and data segments. Code segments are units of calcu- lation which have no state. Data segments are sets of typed data. Code segments are connected to data segments by a meta data segment called a context. After the execution of a code have input data segments and output data segments. Data segment and its context, the next code segment (continuation) segments have two kind of dependency with code segments. is executed. First, Code segments access the contents of data segments Continuation based C (CbC) [1], hereafter referred to as using field names. So data segments should have the named CbC, is a slight modified C which supports code segments. -
Register Allocation and Method Inlining
Combining Offline and Online Optimizations: Register Allocation and Method Inlining Hiroshi Yamauchi and Jan Vitek Department of Computer Sciences, Purdue University, {yamauchi,jv}@cs.purdue.edu Abstract. Fast dynamic compilers trade code quality for short com- pilation time in order to balance application performance and startup time. This paper investigates the interplay of two of the most effective optimizations, register allocation and method inlining for such compil- ers. We present a bytecode representation which supports offline global register allocation, is suitable for fast code generation and verification, and yet is backward compatible with standard Java bytecode. 1 Introduction Programming environments which support dynamic loading of platform-indep- endent code must provide supports for efficient execution and find a good balance between responsiveness (shorter delays due to compilation) and performance (optimized compilation). Thus, most commercial Java virtual machines (JVM) include several execution engines. Typically, there is an interpreter or a fast com- piler for initial executions of all code, and a profile-guided optimizing compiler for performance-critical code. Improving the quality of the code of a fast compiler has the following bene- fits. It raises the performance of short-running and medium length applications which exit before the expensive optimizing compiler fully kicks in. It also ben- efits long-running applications with improved startup performance and respon- siveness (due to less eager optimizing compilation). One way to achieve this is to shift some of the burden to an offline compiler. The main question is what optimizations are profitable when performed offline and are either guaranteed to be safe or can be easily validated by a fast compiler. -
Intermediate Representation and LLVM
CS153: Compilers Lecture 6: Intermediate Representation and LLVM Stephen Chong https://www.seas.harvard.edu/courses/cs153 Contains content from lecture notes by Steve Zdancewic and Greg Morrisett Announcements •Homework 1 grades returned •Style •Testing •Homework 2: X86lite •Due Tuesday Sept 24 •Homework 3: LLVMlite •Will be released Tuesday Sept 24 Stephen Chong, Harvard University 2 Today •Continue Intermediate Representation •Intro to LLVM Stephen Chong, Harvard University 3 Low-Level Virtual Machine (LLVM) •Open-Source Compiler Infrastructure •see llvm.org for full documentation •Created by Chris Lattner (advised by Vikram Adve) at UIUC •LLVM: An infrastructure for Multi-stage Optimization, 2002 •LLVM: A Compilation Framework for Lifelong Program Analysis and Transformation, 2004 •2005: Adopted by Apple for XCode 3.1 •Front ends: •llvm-gcc (drop-in replacement for gcc) •Clang: C, objective C, C++ compiler supported by Apple •various languages: Swift, ADA, Scala, Haskell, … •Back ends: •x86 / Arm / PowerPC / etc. •Used in many academic/research projects Stephen Chong, Harvard University 4 LLVM Compiler Infrastructure [Lattner et al.] LLVM llc frontends Typed SSA backend like IR code gen 'clang' jit Optimizations/ Transformations Analysis Stephen Chong, Harvard University 5 Example LLVM Code factorial-pretty.ll define @factorial(%n) { •LLVM offers a textual %1 = alloca %acc = alloca store %n, %1 representation of its IR store 1, %acc •files ending in .ll br label %start start: %3 = load %1 factorial64.c %4 = icmp sgt %3, 0 br %4, label -
Ryan Holland CSC415 Term Paper Final Draft Language: Swift (OSX)
Ryan Holland CSC415 Term Paper Final Draft Language: Swift (OSX) Apple released their new programming language "Swift" on June 2nd of this year. Swift replaces current versions of objective-C used to program in the OSX and iOS environments. According to Apple, swift will make programming apps for these environments "more fun". Swift is also said to bring a significant boost in performance compared to the equivalent objective-C. Apple has not released an official document stating the reasoning behind the launch of Swift, but speculation is that it was a move to attract more developers to the iOS platform. Swift development began in 2010 by Chris Lattner, but would later be aided by many other programmers. Swift employs ideas from many languages into one, not only from objective-C. These languages include Rust, Haskell, Ruby, Python, C#, CLU mainly but many others are also included. Apple says that most of the language is built for Cocoa and Cocoa Touch. Apple claims that Swift is more friendly to new programmers, also claiming that the language is just as enjoyable to learn as scripting languages. It supports a feature known as playgrounds, that allow programmers to make modifications on the fly, and see results immediately without the need to build the entire application first. Apple controls most aspects of this language, and since they control so much of it, they keep a detailed records of information about the language on their developer site. Most information within this paper will be based upon those records. Unlike most languages, Swift has a very small set of syntax that needs to be shown compared to other languages. -
Generalizing Loop-Invariant Code Motion in a Real-World Compiler
Imperial College London Department of Computing Generalizing loop-invariant code motion in a real-world compiler Author: Supervisor: Paul Colea Fabio Luporini Co-supervisor: Prof. Paul H. J. Kelly MEng Computing Individual Project June 2015 Abstract Motivated by the perpetual goal of automatically generating efficient code from high-level programming abstractions, compiler optimization has developed into an area of intense research. Apart from general-purpose transformations which are applicable to all or most programs, many highly domain-specific optimizations have also been developed. In this project, we extend such a domain-specific compiler optimization, initially described and implemented in the context of finite element analysis, to one that is suitable for arbitrary applications. Our optimization is a generalization of loop-invariant code motion, a technique which moves invariant statements out of program loops. The novelty of the transformation is due to its ability to avoid more redundant recomputation than normal code motion, at the cost of additional storage space. This project provides a theoretical description of the above technique which is fit for general programs, together with an implementation in LLVM, one of the most successful open-source compiler frameworks. We introduce a simple heuristic-driven profitability model which manages to successfully safeguard against potential performance regressions, at the cost of missing some speedup opportunities. We evaluate the functional correctness of our implementation using the comprehensive LLVM test suite, passing all of its 497 whole program tests. The results of our performance evaluation using the same set of tests reveal that generalized code motion is applicable to many programs, but that consistent performance gains depend on an accurate cost model. -
Efficient Symbolic Analysis for Optimizing Compilers*
Efficient Symbolic Analysis for Optimizing Compilers? Robert A. van Engelen Dept. of Computer Science, Florida State University, Tallahassee, FL 32306-4530 [email protected] Abstract. Because most of the execution time of a program is typically spend in loops, loop optimization is the main target of optimizing and re- structuring compilers. An accurate determination of induction variables and dependencies in loops is of paramount importance to many loop opti- mization and parallelization techniques, such as generalized loop strength reduction, loop parallelization by induction variable substitution, and loop-invariant expression elimination. In this paper we present a new method for induction variable recognition. Existing methods are either ad-hoc and not powerful enough to recognize some types of induction variables, or existing methods are powerful but not safe. The most pow- erful method known is the symbolic differencing method as demonstrated by the Parafrase-2 compiler on parallelizing the Perfect Benchmarks(R). However, symbolic differencing is inherently unsafe and a compiler that uses this method may produce incorrectly transformed programs without issuing a warning. In contrast, our method is safe, simpler to implement in a compiler, better adaptable for controlling loop transformations, and recognizes a larger class of induction variables. 1 Introduction It is well known that the optimization and parallelization of scientific applica- tions by restructuring compilers requires extensive analysis of induction vari- ables and dependencies -
Code Transformation and Analysis Using Clang and LLVM Static and Dynamic Analysis
Code transformation and analysis using Clang and LLVM Static and Dynamic Analysis Hal Finkel1 and G´abor Horv´ath2 Computer Science Summer School 2017 1 Argonne National Laboratory 2 Ericsson and E¨otv¨osLor´adUniversity Table of contents 1. Introduction 2. Static Analysis with Clang 3. Instrumentation and More 1 Introduction Space of Techniques During this set of lectures we'll cover a space of techniques for the analysis and transformation of code using LLVM. Each of these techniques have overlapping areas of applicability: Static Analysis LLVM Instrumentation Source Transformation 2 Space of Techniques When to use source-to-source transformation: • When you need to use the instrumented code with multiple compilers. • When you intend for the instrumentation to become a permanent part of the code base. You'll end up being concerned with the textual formatting of the instrumentation if humans also need to maintain or enhance this same code. 3 Space of Techniques When to use Clang's static analysis: • When the analysis can be performed on an AST representation. • When you'd like to maintain a strong connection to the original source code. • When false negatives are acceptable (i.e. it is okay if you miss problems). https://clang-analyzer.llvm.org/ 4 Space of Techniques When to use IR instrumentation: • When the necessary conditions can be (or can only be) detected at runtime (often in conjunction with a specialized runtime library). • When you require stronger coverage guarantees than static analysis. • When you'd like to reduce the cost of the instrumentation by running optimizations before the instrumentation is inserted, after the instrumentation is inserted, or both. -
LLVM Overview
Overview Brandon Starcheus & Daniel Hackney Outline ● What is LLVM? ● History ● Language Capabilities ● Where is it Used? What is LLVM? What is LLVM? ● Compiler infrastructure used to develop a front end for any programming language and a back end for any instruction set architecture. ● Framework to generate object code from any kind of source code. ● Originally an acronym for “Low Level Virtual Machine”, now an umbrella project ● Intended to replace the GCC Compiler What is LLVM? ● Designed to be compatible with a broad spectrum of front ends and computer architectures. What is LLVM? LLVM Project ● LLVM (Compiler Infrastructure, our focus) ● Clang (C, C++ frontend) ● LLDB (Debugger) ● Other libraries (Parallelization, Multi-level IR, C, C++) What is LLVM? LLVM Project ● LLVM (Compiler Infrastructure, our focus) ○ API ○ llc Compiler: IR (.ll) or Bitcode (.bc) -> Assembly (.s) ○ lli Interpreter: Executes Bitcode ○ llvm-link Linker: Bitcode (.bc) -> Bitcode (.bc) ○ llvm-as Assembler: IR (.ll) -> Bitcode (.bc) ○ llvm-dis Disassembler: Bitcode (.bc) -> IR (.ll) What is LLVM? What is LLVM? Optimizations History History ● Developed by Chris Lattner in 2000 for his grad school thesis ○ Initial release in 2003 ● Lattner also created: ○ Clang ○ Swift ● Other work: ○ Apple - Developer Tools, Compiler Teams ○ Tesla - VP of Autopilot Software ○ Google - Tensorflow Infrastructure ○ SiFive - Risc-V SoC’s History Language Capabilities Language Capabilities ● Infinite virtual registers ● Strongly typed ● Multiple Optimization Passes ● Link-time and Install-time