The algorithms illustrated are claimed to have the same run time efficiency, o r 3, as shown in earlier papers, but require a single examination of each assignment statement. Briefly, in one embodiment, the invention is a method for eliminating common subexpressions in an initial ssa intermediate language representation of at least a portion of a computer program. A stateoftheart register allocator is among the most complicated parts of a compiler, partly because register allocation is npcomplete in general. Compiler construction 20092010 ssastatic single assignment form peter thiemann march 15, 2010. Advantages of ssa over usedef chains flavors of ssa dominance frontiers inserting. The static singleassignment ssa form of a program provides data flow information in a form which makes some compiler optimizations easy to perform. Static single assignment form and the control dependence graph.
Efficiently computing static single assignment form and. Many modern compilers feature intermediate representations ir based on the static single assignment form ssa form. The design and implementation of a ssabased register. According to the wikipedia page on static single assignment ssa, ssa is used by large and wellknown projects such as llvm, gcc, msvc, mono, dalvik, spidermonkey, and v8 while the page on projects using continuationpassing style cps is a bit lacking in comparison.
Compiler developers cite many qualitative reasons for choosing ssa. Static single assignment ssa form is a program representation that is useful for compilerbased code optimization. Compiler design single static assignment consider the following code segment. Static single assignment form for messagepassing programs. Over the past 20 years, static single assignment form ssa has risen to become the compiler intermediate representation of choice. May 01, 2017 i am working on a compiler that uses ssa for a language which contains global variables. Static single assignment book wednesday 30th may, 2018. Everyone seems quite aware of the pros, so let me try to cover the cons. Verified construction of static single assignment form. Pdf singlepass generation of static singleassignment form for. We describe static single assignment ssa based algorithms to build up an intermediate representation of a sequential program while targeting code generation for distributed memory machines employing the single program multiple data spmd model of programming. According to the wikipedia page on staticsingle assignment ssa, ssa is used by large and wellknown projects such as llvm, gcc, msvc, mono, dalvik, spidermonkey, and v8 while the page on projects using continuationpassing style cps is a bit lacking in comparison.
Static singleassignment form arranges for every value computed by a program to have a unique assignment aka, definition a procedure is in ssa form if every variable has statically exactly one definition ssa form simplifies several important optimizations, including various forms of redundancy elimination. In compiler design, static single assignment form often abbreviated as ssa form or ssa is an intermediate representation ir in which every variable is assigned exactly once. Tracedriven, justintime compilation with a new application. Sebastian buchwald, denis lohner, sebastian ullrich, verified construction of static single assignment form, proceedings of the 25th international conference on compiler construction, march 1718, 2016, barcelona, spain. Embedded justintime compilers also tend to use less ambitious data structures than unconstrained compilersfor example, while the use of static single assignment ssa form is fairly standard in large justintime compilers running on serverclass machines, the time and memory needed to convert the 10% most frequently executed methods to. A compiler translates a program in a source language to a program in a target language. The development of static single assignment form kenneth zadeck naturalbridge, inc. Jul 12, 2011 static single assignment for functional programmers. The elimination of the goto results in a program structure that enables the generation and insertion of phi assignments in a single pass during the parsing process. In particular, from nowhere in the program do we jump into the middle of the. Computing static single assignment form computing control dependencies identify natural loops in cfg all nodes x dominated by entry node h, where x can reach h, and there is exactly one back edge head dominates tail in loop why are dominators useful. If you want to retain definitions of variables upon reentry to subprograms, you must use the save attribute. Interprocedural static single assignment form tspace repository. The most well known form of a compiler is one that translates a high level language like c into the native assembly language of a machine so that it can be executed.
Computing static single assignment ssa form overview. The static single assignment form indian institute of. Simple and efficient construction of static single assignment form. I am wondering how i should implement uses and definitions of global variables, for example how should i convert the below code. Im writing a compiler for a registerbased bytecode to an ir with static single assignment ssa form specifically, from dalvik vm bytecode to llvm ir, but im hoping the question can be taken for the general topic and am wondering the best, or theoretically cleanest way to go about this. The arc here is away from the machine, and towards more abstraction, in order to be. This video explains the concept of static single assignment.
The design and implementation of a ssabased register allocator. Structural encoding of static single assignment form andreas gal christian w. Static single assignment form and dominators, postdominators, dominance frontiers cs252r spring 2011 almost all slides shamelessly stolen from. Mar 21, 2016 everyone seems quite aware of the pros, so let me try to cover the cons. Static declarations only affect how data is allocated in storage.
The method includes a inserting a phinode for an unambiguous definition used in an unambiguous subexpression reaching a join point in the initial intermediate language subsequent to the join point. Pdf using software metrics to evaluate static single. Download jflex script which contains paths to the java compiler and jflex classes. The name static single assignment form came from the fact that single assignment. Verified construction of static singleassignment form lohnerformalssa. Adding static single assignment form and a graph coloring. Using software metrics to evaluate static single assignment. Us6002879a method for performing common subexpression. I am working on a compiler that uses ssa for a language which contains global variables. Socalled minimal ssa is not minimal in any meaningful sense, and so pr. In compiler design, static single assignment form often abbreviated as ssa form or simply ssa is a property of an intermediate representation ir, which requires that each variable is assigned exactly once, and every variable is defined. Static single assignment ssa cfgs but with immutable variables plus a slight hack to make graphs work out now widely used e.
Efficiently computing static single assignment form and the control dependence graph ron cytron, jeanne ferrante, barry k. Prior work 3 has conjectured that the use of ssa form could be bene. Over the last few years, static single assignment ssa form 5 has been established as a suitable. Efficiently computing static single assignment form and the. Single assignment is the only form of assignment available in purely functional languages, such as haskell, which do not have variables in the sense of imperative programming languages but rather named constant values possibly of compound nature with their elements progressively defined ondemand. Design and implementation of a static single assignment form. Singlepass generation of static singleassignment form. Most of the tree optimizers rely on the data flow information provided by the static single assignment ssa form. Design and implementation of a static single assignment. Single static assignment optimization mikroelektronika.
Sebastian buchwald, denis lohner, sebastian ullrich, verified construction of static single assignment form, proceedings of the 25th international conference. Static single assignment ssa is an intermediate representation ir that simplifies the design and implementation of analyses and optimizations. Translating out of static single assigment form lncs 1694. Simple generation of static singleassignment form springerlink. Modern compilers use an intermediate representation in static single assignment ssa form, which simplifies many optimizations. What are the pros and cons of using single static assignment.
Multiple assignments to the same variable create new versions of that variable. Efficiently computing static single assignment form and the control. An ssabased compiler modifies the program representation so that every time a variable is assigned in the original. Originally written and maintained by michael van acken and erick nikitin classictoolsooc. Ssa form in this lecture we introduce static single assignment ssa form this is a way of structuring the intermediate representation so that every variable is assigned exactly once this is formally equivalent to.
Home conferences cc proceedings cc 2016 verified construction of static single assignment form. We describe static single assignment ssa based algorithms to build up an intermediate representation of a sequential program while targeting code generation for distributed memory machines employing the single program multiple data spmd. Optimizing oberon2 compiler ooc based on static single assignment ssa representation also known as ooc2. Over the past 20 years, static single assignment form ssa. In compiler design, static single assignment form often abbreviated as ssa form or simply ssa is a property of an intermediate representation ir, which requires that each variable is assigned exactly once, and every variable is defined before it is used. Verified construction of static singleassignment form github. Package ssa defines a representation of the elements of go programs packages, types, functions, variables and constants using a static singleassignment ssa form intermediate representation ir for the bodies of functions. We present a new static single assignment form which can be used by an optimizing compiler as its internal representation and the microarchitecture as its.
Efficiently computing static single assignment form and the control dependence graph. Kenneth zadeck brown university in optimizing compilers, data structure choices directly influence the power and efficiency of practical program optimization. Simple and efficient construction of static single assignment. By default, the compiler allocates local scalar variables of nonrecursive subprograms in the static storage area. Methods to implement a registerbased ir in static single. The value of ssa form is that many popular compiler optimizations constant propagation, e. Originally written and maintained by michael van acken and erick nikitin. Mar 07, 2019 static declarations only affect how data is allocated in storage. Net compiler platform sdk roslyn apis microsoft docs. Probst michael franz 1 donald bren school of information and computer science university of california irvine, ca, 92697, usa abstract static single assignment ssa form is often used as an intermediate representation during code optimization in java virtual machines.
This paper presents a novel scheme for maintaining accurate information about distributed data in messagepassing programs. Originally written and maintained by michael van acken and erick nikitin classicto. While intraprocedural ssa is ubiquitous in modern compilers, the use of interprocedural ssa issa, although seemingly a natural extension, is limited. Because you can use this single codebase, you can write analyzers and code fixes more easily by leveraging the syntactic and semantic analysis apis provided by the. Many modern compilers feature intermediate representations ir based on the. Structural encoding of static single assignment form. However in this study, we present clear quantitative benefits of ssa, by applying several standard software. Aug 08, 2017 this video explains the concept of static single assignment. It is decidedly nontrivial to take a given program and produce a sanely efficient set of phi nodes. In the next assignment, this file will be automatically generated. Static single assignment 15411 compiler design september 23, 2008. Compiler developers cite many qualitative reasons for. In compiler design, static single assignment form is a property of an intermediate representation ir, which requires that each variable is assigned exactly once.
Static single assignment enables the e cient implementation of many important deompilerc ompconents, including expression propagation, preservation analysis, type analysis, and the analysis of indircte jumps and alcls. Interprocedural static single assignment form tspace. Practical improvements to the construction and destruction of static. Single assignment compiler, single assignment architecture. However it does not help the implementor of a compiler to a normal machine, and intermediate languages are all about utility. Directed acyclic graphs dags in compiler design explained step by step. However it does not help the implementor of a compiler to a normal machine, and intermediate languages are all. Modern compilers use intermediate representations in static single assignment ssa form, which simplifies many optimizations. Single static assignment optimization introduction. However, the high implementation complexity of efficient ssa construction algorithms poses a challenge to verified compilers. Source code is an essential part of all software development. Outline 1 static singleassignment form 2 converting to ssa form 3 optimization algorithms using ssa 4 dependencies. Pdf simple and efficient construction of static single assignment. Citeseerx document details isaac councill, lee giles, pradeep teregowda.
367 350 114 206 1027 597 49 1064 312 319 1351 202 932 778 309 229 1203 1450 724 125 1263 243 245 910 18 969 1363 812 243 852 1358 1265 376 1196 59 1175 1269 644 1381 1194 120 1343