Developing Optimizations

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DevelopingOptimizationsProgrammable Optimization AndEmpirical Tuning7/11/2014DragonStar 2014 - Qing Yi1

Outlinep Programmable composition ofoptimizationsn Pattern-based optimization compositionp p E.g., dense matrix codes, stencils, graphsEmpirical tuningn 7/11/2014Searching the optimization spaceDragonStar 2014 - Qing Yi2

Programmable Optimization and Empirical Tuningp 7/11/2014Goal: customizable programoptimization environmentn Analysis engine(compiler) interacts withdevelopersp Use the ROSE C/C compilern Analysis resultsexpressed in POETp An open-sourceprogramtransformationscripting languagewww.cs.uccs.edu/ qyi/poetp Programmable controlby developersn POET transformationsempirically tunedDragonStar 2014 - Qing Yi3

What is POET?p It is a scripting language forn n n p Applying parameterized program transformationsProgrammable control of compiler optimizationsAd-hoc translation between arbitrary languagesDeveloped since 2007 at UTSA and UCCSn n Open source (BSD license)Language documentation and download availableatp www.cs.uccs.edu/ qyi/poetFeedback welcome and appreciated7/11/2014DragonStar 2014 - Qing Yi4

Use Cases Of POETp Parameterization of Optimizations forEmpirical Tuningn n p Programmable control of compileroptimizationsn p Lightweight portable program transformationengineParameterized at the finest granularityFlexible composition of independently defined optsDomain-specific code generation/ad-hoctranslationn 7/11/2014Source-to-source translator among arbitrarylanguagesDragonStar 2014 - Qing Yi5

An example POET scriptinclude opt.pip parameter inFile message "input file"/ parameter outFile message "output file"/ parameter p threads default (2) / parameter b factor default (32) / parameter p block default (256 ) / trace inputCode,Nest1,Nest2,Nest3,Nest4 / Can be autogenerated fromhigher-leveltransformationspecifications input from inFile syntax "Cfront.code"to inputCode / eval BlockLoops[factor p block](Nest2 grp3[Nest.body],Nest2 grp3); / output to outFile syntax "Cfront.code"from inputCode / 7/11/2014DragonStar 2014 - Qing Yin n n Invokes predefinedoptimizations in thePOET opt.pt librarySimple input/outputcommandsDynamically tracep p n Input code fragmentsResult oftransformationsFlexible compositionof optimizations6

Example Annotated Input Codevoid dgemm test(const int M,const int N,const int K,const double alpha,const double*A,const int lda,const double *B,const int ldb,const double beta,double *C,const int ldc){int I,j,l;/*@; BEGIN(nest1 Nest) @*/for (j 0; j -1 N; j 1) {/*@; BEGIN(nest3 Nest) @*/for (i 0; i -1 M; i 1) {C[(j * ldc) i] (beta * (C[(j * ldc) i]));/*@; BEGIN(nest2 Nest) @*/for (l 0; l -1 K; l 1) {C[(j * ldc) i] ((C[(j * ldc) i]) ((alpha * (A[(l * lda) i])) * (B[(j * ldb) l])));} } } }p Each loop to be optimized is given a handle namen n 7/11/2014POET transformations can directly operate on these handlesEach transformation modifies the handles to containequivalent optimized codeDragonStar 2014 - Qing Yi7

Domain-Specific Optimizationp Utilize domain knowledge from the HPCn n n p E.g., strategies for stencil code and dense matricesTrace key components of input code (e.g., loops)Apply optimizations known to be beneficialSupport small annotation and specificationlanguagesn Quickly translate between ad-hoc languagesp n Map multiple languages to a single ASTp p 7/11/2014E.g., tester/timer generation, dependence oroptimization specificationInput: read in the AST using one syntaxOutput: unparse the AST using a different syntaxDragonStar 2014 - Qing Yi8

Empirical Tuning of POET ScriptsFinal optconfig.SearchengineRuntimefeedbackp DeveloperPOET scriptInput code POET scriptParameter valuesPOETxformengineOptimizedcode driverExecutableVentor compiler(gcc)Used POET to parse parameter declarations and construct searchspace description7/11/2014DragonStar 2014 - Qing Yi9

The POET Optimization Libraryp p Defined in POET/lib/opt.pt (interface in opt.pi)Loop optimizationsn Targeting multi-core architecturesp n Targeting memory performancep n Loop blocking, interchange, fusion, fission, skewingTargeting register-level performancep p OpenMP loop parallelizationLoop unroll&jam, unrolling, SSE vectorizationData layout optimizationsn Reducing the cost of array referencesp 7/11/2014Array copying, scalar replacement, strength reductionDragonStar 2014 - Qing Yi10

Required Xform Parametersp Single loop xforms: Op [optional params] (loop)n Operate on a given loop xp p p Loop nest xforms : Op [optional params] (inner,outer)n Operate between an inner body n and an outer loop xp p p ParallelizeLoop(x): OpenMP loop parallelizationCleanupBlockedNests(x): generate cleanup codeUnrollLoops(n,x)/UnrollJam(n,x): Loop ,x): loop blocking/interchangeOther xforms: opt[optional params](config, loop)n Operate on input x based on various configurationsp p p p p 7/11/2014DistributeLoops(bodiesToDist,x): distribute loop xFuseLoops(nestsToFuse,pivot): replace pivot with fused loopVectorizeLoop(r, x): loop vectorization using register assign rCopyRepl(ref,dim, x): copy memory accessed by arraysScalarRepl(ref,dim,x): use scalars to substitute memoryDragonStar 2014 - Qing Yi11

Optional Xform Parametersp Configuration parametersn factor: a list of integer blocking/unrolling factorsp n cleanup (1/0/-1): whether to generate cleanup code.p p p p p Default values are set to commonly used onescleanup 1: generate cleanup code now;cleanup -1: there is no need for cleanup codecleanup 0: will generate cleanup later (not now)By default, cleanup code is generated now (i.e., cleanup 1)Side-effects parameters: handles used to save resultsn n n n n 7/11/2014trace: result handle to save transformations to inputtrace cleanup: result handle for generated cleanup codetrace decl: result handle for inserting variable declarationstrace include: result handle for adding new include files;trace mod: trace the modification of a list of expressionsDragonStar 2014 - Qing Yi12

POET Data Typesp Atomic types and associated operationsn p Integers and stringsCompound types and associated operationsn Lists: a singly linked listp p n Tuples: a static finite sequence of valuesp p n p p Construction: Loop[maxIter 100]#(“I”,0,”m”,1), Nest#(c, b)Accessing components: n[Nest.ctrl], c[Loop.I]Handles: special variables used to track AST transformsp 7/11/2014Construction: MAP{“a” 1,”b” 2} or MAP(type1, type2)Accessing components: m[“a”] 3, b m[“b”]Code templates(ASTs): user defined types in POETp n Construction: (a,b,c,d)Accessing components: t[index] where index is an integerMaps: associate pairs of related valuesp n Construction: (a b c), a::bAccessing components: HEAD(l), TAIL(l)Can be modified by xform routines via side effectsDragonStar 2014 - Qing Yi13

Example: Loop Unrollinginclude opt.pi parameter out default "" message "output file location" / parameter ur parse INT default 2 message "Loop unrolling factor for target"/ trace inputCode,target/ input from "mgrid.f" syntax "Ffront.code" to inputCode/ eval UnrollLoops[factor ur;trace inputCode](target[Nest.body],target); / output to out syntax "Ffront.code" from (inputCode)/ p p Unroll the loop tagged by target in “mgrid.f”To tune optimizationn 7/11/2014pcg -pout “out.f” -pur 4 opt unroll.ptDragonStar 2014 - Qing Yi14

Writing Your Own Optimizationsp POET xforms are oblivious of language syntaxn p Each optimization is a routine (global function)whichn n n p Traverses the AST to collect informationModifies the AST using built-in operationsMaintains the consistency of embedded handlesPOET support for building optimizationsn n n p Operate on ASTs shared by different languagesPattern matching and pattern-based traversalC-like control flow and recursive functionsHandle aware transformation operationsGetting started:n 7/11/2014Use PRINT and DEBUG operations for debuggingDragonStar 2014 - Qing Yi15

Example: Collecting Information xform FindLoopsInNest pars (inner, input) if (input : inner) {“” } * reaching inner, stopelse if (input : Nest#(loop,body))? {innerloops FindLoopsInNest(inner, body); * recursion(innerloops "")? loop : loop::innerloops; * concatenate}else ERROR(“Did not find inner body: ” inner); /xform p Find all the loops outside inner and inside inputn p Pattern matching:n n p Recursively navigates down input until reaching innerx:yDoes x equal to y or match the structure of y?input : Nest#(loop,body) : is input a Nest? if yes, use loop and body tosave its childrenList concatenation: x :: yn 7/11/2014Build a new list with x as the first element followed by yDragonStar 2014 - Qing Yi16

Example: Pattern-based Traversal xform FindStmtsOutsideNest pars (nest, input) res NULL;foreach (input : (cur (nest ExpStmt)) : TRUE) {if (cur ! nest) res cur::res;}ReverseList(res) /xform p Find all ExpStmts that are outside nest and inside inputn p The last expression ReverseList(res) is returned as resultAST traversal loop: evaluates body for each matching ASTp n n n succ true : do not traverse inside the matching ASTssucc false : continue traversal inside each matching ASTTo traverse input in reverse orderp 7/11/2014foreach (input : pattern : succ) bodyforeach r (input : pattern : succ) bodyDragonStar 2014 - Qing Yi17

Using Maps To Save Information xform MapLoopsInNest pars (input, map) foreach (input : (cur Nest#((CLEAR loop), )): FALSE){if (map[loop] "") map[loop] cur;else map[loop] cur :: map[loop];} /xform p Map each loop control in input to the whole loopn Among all POET compound data structures, Maps arethe only type of value that can be modifiedp p E.g., you can build a new list, but not modify an existing one,as different lists may share internal componentsPattern specifiersn n n 7/11/2014cur pattern: use cur to save the matched ASTCLEAR var : uninitialize var so that it matches anarbitray value and then saves the matched value: matches an arbitrary value (without saving it)DragonStar 2014 - Qing Yi18

Developing Program Xformsp A program transformation takes an input ASTand returns a new onen n For optimization purposes, the new code must beequivalent to the original oneMay want to modify the original AST directlyp p E.g., to keep a single version of working ASTEach POET transformation is an operationthatn n Takes an AST and returns the transformed oneModifies the input AST if it contains result handlesp 7/11/2014An AST cannot be directly modified as different ASTsmay share common componentsDragonStar 2014 - Qing Yi19

Support Of AST Transformationsp Built-in AST transforming operations (input AST: e)n n REPLACE(c1,c2,e): replace all occurrences of c1 with c2REPLACE(((o1 ,r1 ).(om, rm)), e)p p n REBUILD(e) : rebuild the input ASTp n Each copy replacing c1 by a different component in c2PERMUTE( (I 1 , I 2 , ., I m),e): reorder the input listp p p Invoke an associated rebuild routine for each AST nodeDUPLICATE(c1,c2,e): replicate input ASTp n Locate and replace each oi (i 1,.,m) with riMust encounter o1, ,om in order in pre-order traversal of eThe input must be a list of AST nodesThe j th (j 1,.,m) element is located at I j in the resultAll transformations return a single list/AST as resultn 7/11/2014Modify trace handles inside the input AST if appropriateDragonStar 2014 - Qing Yi20

Handles In POETp A special kind of global variablesn n p Lifetime span all POET files in a programCan be embedded inside ASTs to tracetransformationsHandles can be declared in groupsp n n 7/11/2014 trace inputCode, nest1, nest3, nest2/ They are encountered in order in a pre-ordertraversal of inputThey are used as input/output of POET xformroutinesDragonStar 2014 - Qing Yi21

Handle Operationsp Insertion and removal of handles (input AST: e)n INSERT (x, e): insert handle x inside input AST ep p n ERASE(x, e): remove all occurrences of handle x from ep n p All handles following x in the same group are also insertedAll handles must already contain fragments of e as valuesDoes not affect other handles in the same groupCOPY(e): remove all handles in e and return the resultMust save modification result unless input is itselfa handlen 7/11/2014In which case the input handle is modified to containresultDragonStar 2014 - Qing Yi22

Example: Erase Handles xform EraseTraceHandle pars (handle, trace) nested handle TRUErepl " keep” trace ERASE(handle, trace);for (origvlaue ERASE(handle); * return the value of handle * origvalue : VAR && nested handle; origvalue ERASE(origvalue)){ trace ERASE(origvalue, trace); }if (repl ! " keep") trace REPLACE(origvalue, repl, trace);(origvalue, trace) /xform p Erase a handle from an input AST tracen n Return the value of handle and modified traceTrace handles may directly nest inside one anotherp p Erase nested handles holding the same valueUse tuple to directly return multiple values to the caller7/11/2014DragonStar 2014 - Qing Yi23

Example: Modify Handles xform ModifyTraceHandle pars (handle, newvalue)trace "” nested handle TRUE (handle1, newvalue) EraseTraceHandle(handle, newvalue);REPLACE(handle1, newvalue, handle) /xform p Modify handle with a new valuen n p trace: handle containing the overall ASTReturn the modified handle or traceGoal: avoid creating any cycles in ASTn n 7/11/2014The input newvalue may contain handle ascomponentsNeed to erase handle from trace or newvaluebefore replacementDragonStar 2014 - Qing Yi24

POET Code Templatesp Code templates are user-defined data types thatn Can be used to build compound acyclic data structuresp n n p To avoid cycles, internal data members cannot be modifiedCan be associated with concrete syntaxes for parsing/unparsingCan be used to automatically build ASTs for arbitrarylanguagesFor example code GraphEdge pars (from:GraphNode,to:GraphNode) "@from@"- "@to@" /code n n Data members of data structure: from and toSyntax of data structure: the body of GraphEdgep p n Type annotations for data members: GraphNodep 7/11/2014Used to automatically convert GraphEdge to/from stringsThe @ @ sign: used to surround a POET expressionUsed to specify how to parse/unparse each data memberDragonStar 2014 - Qing Yi25

Example: From C2F.code code VoidType subroutine /code code IntType pars (name:"char" "int" "unsigned" "long") @(switch(name){case "char": "integer*1"case ("int" "unsigned"): "integer"case "long" : "integer*4"})@ /code p Map C concepts to Fortrann n 7/11/2014Redefine syntax for common conceptsMay need to use global variables or tables to saveinformationDragonStar 2014 - Qing Yi26

Example: Loop Permutation xform PermuteLoops pars (inner,input) order 0 trace "" if (order 0) { input }else if (! (input : Nest#(loop,body)) ) {ERROR("Input is not a loop nest!")}else {loops FindLoopsInNest(inner, input);if (LEN(loops) ! LEN(order))ERROR("Incorrect reordering indices: " order "\n Loops are: " loops);nloops PERMUTE (order, loops);res BuildNest(nloops, inner);res TraceNestedLoops[trace input](nests, res);if (trace : VAR) REPLACE(ERASE(input), res, trace);else { res } } /xform p Key: modify handles in AST with correct values7/11/2014DragonStar 2014 - Qing Yi27

Domain-specific Code Generationp Use code templates to represent domainspecific conceptsn n n p Define a compound data type for each conceptSpecify how to parse and unparse the data typeNo need to express everything using statementsExample: generating testing driversn Code templates could be defined forp n n 7/11/2014Allocate buffer, parameter initialization, initialize timer,reading timing, The generated timer could be in C, Fortran, or anyother languageJust like translating programs from one language toanotherDragonStar 2014 - Qing Yi28

Example: Timer Generation code StaticBufferAllocate pars (type,name,size,align,nrep) @name@ size @TimerAlignSize#(size,align)@; @ (if (nrep 1) { @@name@ rep CacheSZ / @name@ size 1; @})@ /code code Static2DBufferAllocate pars (type,name,size,size2,align,nrep) @name@ size @TimerAlignSize#(size,align)@; @ (if (nrep 1) { @@name@ rep CacheSZ / @name@ size 1; @})@@name@ size2 @TimerAlignSize#(size2,align)@; /code code TimerBufferInitialize pars (name, nrep, value, valueIncr) /code "p No details of the underlying language7/11/2014DragonStar 2014 - Qing Yi29

Summaryp Compose optimizations using POETn n p Writing your own analysis or optimizationn n n n p Invoke routines from the opt libraryFrom high-level specifications to POET scriptsDefinition of code templatesUse of built-in typesTraversing the ASTModifying the AST through handlesTuning of optimizationsn 7/11/2014Navigating meaningful combinations of parametervaluesDragonStar 2014 - Qing Yi30

E.g., tester/timer generation, dependence or optimization specification " Map multiple languages to a single AST ! Input: read in the AST using one syntax ! Output: unparse the AST using

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