source: src/GenPoly/Specialize.cc @ 5fcba14

//
// Cforall Version 1.0.0 Copyright (C) 2015 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// Specialize.cc --
//
// Author           : Richard C. Bilson
// Created On       : Mon May 18 07:44:20 2015
// Last Modified By : Peter A. Buhr
// Last Modified On : Thu Mar 16 07:53:59 2017
// Update Count     : 31
//

#include <cassert>                       // for assert, assertf
#include <iterator>                      // for back_insert_iterator, back_i...
#include <map>                           // for _Rb_tree_iterator, _Rb_tree_...
#include <memory>                        // for unique_ptr
#include <string>                        // for string
#include <tuple>                         // for get
#include <utility>                       // for pair

#include "Common/PassVisitor.h"
#include "Common/SemanticError.h"        // for SemanticError
#include "Common/UniqueName.h"           // for UniqueName
#include "Common/utility.h"              // for group_iterate
#include "GenPoly.h"                     // for getFunctionType
#include "InitTweak/InitTweak.h"         // for isIntrinsicCallExpr
#include "Parser/LinkageSpec.h"          // for C
#include "ResolvExpr/FindOpenVars.h"     // for findOpenVars
#include "ResolvExpr/TypeEnvironment.h"  // for OpenVarSet, AssertionSet
#include "Specialize.h"
#include "SynTree/Attribute.h"           // for Attribute
#include "SynTree/Declaration.h"         // for FunctionDecl, DeclarationWit...
#include "SynTree/Expression.h"          // for ApplicationExpr, Expression
#include "SynTree/Label.h"               // for Label
#include "SynTree/Mutator.h"             // for mutateAll
#include "SynTree/Statement.h"           // for CompoundStmt, DeclStmt, Expr...
#include "SynTree/Type.h"                // for FunctionType, TupleType, Type
#include "SynTree/TypeSubstitution.h"    // for TypeSubstitution
#include "SynTree/Visitor.h"             // for Visitor

namespace GenPoly {
        struct Specialize final : public WithTypeSubstitution, public WithStmtsToAdd, public WithVisitorRef<Specialize> {
                Expression * postmutate( ApplicationExpr *applicationExpr );
                Expression * postmutate( CastExpr *castExpr );

                void handleExplicitParams( ApplicationExpr *appExpr );
                Expression * createThunkFunction( FunctionType *funType, Expression *actual, InferredParams *inferParams );
                Expression * doSpecialization( Type *formalType, Expression *actual, InferredParams *inferParams );

                std::string paramPrefix = "_p";
        };

        /// Looks up open variables in actual type, returning true if any of them are bound in the environment or formal type.
        bool needsPolySpecialization( Type *formalType, Type *actualType, TypeSubstitution *env ) {
                if ( env ) {
                        using namespace ResolvExpr;
                        OpenVarSet openVars, closedVars;
                        AssertionSet need, have;
                        findOpenVars( formalType, openVars, closedVars, need, have, false );
                        findOpenVars( actualType, openVars, closedVars, need, have, true );
                        for ( OpenVarSet::const_iterator openVar = openVars.begin(); openVar != openVars.end(); ++openVar ) {
                                Type *boundType = env->lookup( openVar->first );
                                if ( ! boundType ) continue;
                                if ( TypeInstType *typeInst = dynamic_cast< TypeInstType* >( boundType ) ) {
                                        // bound to another type variable
                                        if ( closedVars.find( typeInst->get_name() ) == closedVars.end() ) {
                                                // bound to a closed variable => must specialize
                                                return true;
                                        } // if
                                } else {
                                        // variable is bound to a concrete type => must specialize
                                        return true;
                                } // if
                        } // for
                        // none of the type variables are bound
                        return false;
                } else {
                        // no env
                        return false;
                } // if
        }

        /// True if both types have the same structure, but not necessarily the same types.
        /// That is, either both types are tuple types with the same size (recursively), or
        /// both are not tuple types.
        bool matchingTupleStructure( Type * t1, Type * t2 ) {
                TupleType * tuple1 = dynamic_cast< TupleType * >( t1 );
                TupleType * tuple2 = dynamic_cast< TupleType * >( t2 );
                if ( tuple1 && tuple2 ) {
                        if ( tuple1->size() != tuple2->size() ) return false;
                        for ( auto types : group_iterate( tuple1->get_types(), tuple2->get_types() ) ) {
                                if ( ! matchingTupleStructure( std::get<0>( types ), std::get<1>( types ) ) ) return false;
                        }
                        return true;
                } else if ( ! tuple1 && ! tuple2 ) return true;
                return false;
        }

        // walk into tuple type and find the number of components
        size_t singleParameterSize( Type * type ) {
                if ( TupleType * tt = dynamic_cast< TupleType * >( type ) ) {
                        size_t sz = 0;
                        for ( Type * t : *tt ) {
                                sz += singleParameterSize( t );
                        }
                        return sz;
                } else {
                        return 1;
                }
        }

        // find the total number of components in a parameter list
        size_t functionParameterSize( FunctionType * ftype ) {
                size_t sz = 0;
                for ( DeclarationWithType * p : ftype->get_parameters() ) {
                        sz += singleParameterSize( p->get_type() );
                }
                return sz;
        }

        bool needsTupleSpecialization( Type *formalType, Type *actualType ) {
                // Needs tuple specialization if the structure of the formal type and actual type do not match.
                // This is the case if the formal type has ttype polymorphism, or if the structure  of tuple types
                // between the function do not match exactly.
                if ( FunctionType * fftype = getFunctionType( formalType ) ) {
                        if ( fftype->isTtype() ) return true;
                        // conversion of 0 (null) to function type does not require tuple specialization
                        if ( dynamic_cast< ZeroType * >( actualType ) ) return false;
                        FunctionType * aftype = getFunctionType( actualType->stripReferences() );
                        assertf( aftype, "formal type is a function type, but actual type is not: %s", toString( actualType ).c_str() );
                        // Can't tuple specialize if parameter sizes deeply-differ.
                        if ( functionParameterSize( fftype ) != functionParameterSize( aftype ) ) return false;
                        // tuple-parameter sizes are the same, but actual parameter sizes differ - must tuple specialize
                        if ( fftype->parameters.size() != aftype->parameters.size() ) return true;
                        // total parameter size can be the same, while individual parameters can have different structure
                        for ( auto params : group_iterate( fftype->parameters, aftype->parameters ) ) {
                                DeclarationWithType * formal = std::get<0>(params);
                                DeclarationWithType * actual = std::get<1>(params);
                                if ( ! matchingTupleStructure( formal->get_type(), actual->get_type() ) ) return true;
                        }
                }
                return false;
        }

        bool needsSpecialization( Type *formalType, Type *actualType, TypeSubstitution *env ) {
                return needsPolySpecialization( formalType, actualType, env ) || needsTupleSpecialization( formalType, actualType );
        }

        Expression * Specialize::doSpecialization( Type *formalType, Expression *actual, InferredParams *inferParams ) {
                assertf( actual->result, "attempting to specialize an untyped expression" );
                if ( needsSpecialization( formalType, actual->get_result(), env ) ) {
                        if ( FunctionType *funType = getFunctionType( formalType ) ) {
                                if ( ApplicationExpr * appExpr = dynamic_cast<ApplicationExpr*>( actual ) ) {
                                        return createThunkFunction( funType, appExpr->get_function(), inferParams );
                                } else if ( VariableExpr * varExpr = dynamic_cast<VariableExpr*>( actual ) ) {
                                        return createThunkFunction( funType, varExpr, inferParams );
                                } else {
                                        // This likely won't work, as anything that could build an ApplicationExpr probably hit one of the previous two branches
                                        return createThunkFunction( funType, actual, inferParams );
                                }
                        } else {
                                return actual;
                        } // if
                } else {
                        return actual;
                } // if
        }

        /// restructures the arguments to match the structure of the formal parameters of the actual function.
        /// [begin, end) are the exploded arguments.
        template< typename Iterator, typename OutIterator >
        void structureArg( Type * type, Iterator & begin, Iterator end, OutIterator out ) {
                if ( TupleType * tuple = dynamic_cast< TupleType * >( type ) ) {
                        std::list< Expression * > exprs;
                        for ( Type * t : *tuple ) {
                                structureArg( t, begin, end, back_inserter( exprs ) );
                        }
                        *out++ = new TupleExpr( exprs );
                } else {
                        assertf( begin != end, "reached the end of the arguments while structuring" );
                        *out++ = *begin++;
                }
        }

        /// explode assuming simple cases: either type is pure tuple (but not tuple expr) or type is non-tuple.
        template< typename OutputIterator >
        void explodeSimple( Expression * expr, OutputIterator out ) {
                if ( TupleType * tupleType = dynamic_cast< TupleType * > ( expr->get_result() ) ) {
                        // tuple type, recursively index into its components
                        for ( unsigned int i = 0; i < tupleType->size(); i++ ) {
                                explodeSimple( new TupleIndexExpr( expr->clone(), i ), out );
                        }
                        delete expr;
                } else {
                        // non-tuple type - output a clone of the expression
                        *out++ = expr;
                }
        }

        struct EnvTrimmer {
                TypeSubstitution * env, * newEnv;
                EnvTrimmer( TypeSubstitution * env, TypeSubstitution * newEnv ) : env( env ), newEnv( newEnv ){}
                void previsit( TypeDecl * tyDecl ) {
                        // transfer known bindings for seen type variables
                        if ( Type * t = env->lookup( tyDecl->name ) ) {
                                newEnv->add( tyDecl->name, t );
                        }
                }
        };

        /// reduce environment to just the parts that are referenced in a given expression
        TypeSubstitution * trimEnv( ApplicationExpr * expr, TypeSubstitution * env ) {
                if ( env ) {
                        TypeSubstitution * newEnv = new TypeSubstitution();
                        PassVisitor<EnvTrimmer> trimmer( env, newEnv );
                        expr->accept( trimmer );
                        return newEnv;
                }
                return nullptr;
        }

        /// Generates a thunk that calls `actual` with type `funType` and returns its address
        Expression * Specialize::createThunkFunction( FunctionType *funType, Expression *actual, InferredParams *inferParams ) {
                static UniqueName thunkNamer( "_thunk" );

                FunctionType *newType = funType->clone();
                if ( env ) {
                        // it is important to replace only occurrences of type variables that occur free in the
                        // thunk's type
                        env->applyFree( newType );
                } // if
                // create new thunk with same signature as formal type (C linkage, empty body)
                FunctionDecl *thunkFunc = new FunctionDecl( thunkNamer.newName(), Type::StorageClasses(), LinkageSpec::C, newType, new CompoundStmt() );
                thunkFunc->fixUniqueId();

                // thunks may be generated and not used - silence warning with attribute
                thunkFunc->get_attributes().push_back( new Attribute( "unused" ) );

                // thread thunk parameters into call to actual function, naming thunk parameters as we go
                UniqueName paramNamer( paramPrefix );
                ApplicationExpr *appExpr = new ApplicationExpr( actual );

                FunctionType * actualType = getFunctionType( actual->get_result() )->clone();
                if ( env ) {
                        // need to apply the environment to the actual function's type, since it may itself be polymorphic
                        env->apply( actualType );
                }
                std::unique_ptr< FunctionType > actualTypeManager( actualType ); // for RAII
                std::list< DeclarationWithType * >::iterator actualBegin = actualType->get_parameters().begin();
                std::list< DeclarationWithType * >::iterator actualEnd = actualType->get_parameters().end();

                std::list< Expression * > args;
                for ( DeclarationWithType* param : thunkFunc->get_functionType()->get_parameters() ) {
                        // name each thunk parameter and explode it - these are then threaded back into the actual function call.
                        param->set_name( paramNamer.newName() );
                        explodeSimple( new VariableExpr( param ), back_inserter( args ) );
                }

                // walk parameters to the actual function alongside the exploded thunk parameters and restructure the arguments to match the actual parameters.
                std::list< Expression * >::iterator argBegin = args.begin(), argEnd = args.end();
                for ( ; actualBegin != actualEnd; ++actualBegin ) {
                        structureArg( (*actualBegin)->get_type(), argBegin, argEnd, back_inserter( appExpr->get_args() ) );
                }

                appExpr->set_env( trimEnv( appExpr, env ) );
                if ( inferParams ) {
                        appExpr->get_inferParams() = *inferParams;
                } // if

                // handle any specializations that may still be present
                std::string oldParamPrefix = paramPrefix;
                paramPrefix += "p";
                // save stmtsToAddBefore in oldStmts
                std::list< Statement* > oldStmts;
                oldStmts.splice( oldStmts.end(), stmtsToAddBefore );
                appExpr->acceptMutator( *visitor );
                paramPrefix = oldParamPrefix;
                // write any statements added for recursive specializations into the thunk body
                thunkFunc->statements->kids.splice( thunkFunc->statements->kids.end(), stmtsToAddBefore );
                // restore oldStmts into stmtsToAddBefore
                stmtsToAddBefore.splice( stmtsToAddBefore.end(), oldStmts );

                // add return (or valueless expression) to the thunk
                Statement *appStmt;
                if ( funType->returnVals.empty() ) {
                        appStmt = new ExprStmt( appExpr );
                } else {
                        appStmt = new ReturnStmt( appExpr );
                } // if
                thunkFunc->statements->kids.push_back( appStmt );

                // add thunk definition to queue of statements to add
                stmtsToAddBefore.push_back( new DeclStmt( thunkFunc ) );
                // return address of thunk function as replacement expression
                return new AddressExpr( new VariableExpr( thunkFunc ) );
        }

        void Specialize::handleExplicitParams( ApplicationExpr *appExpr ) {
                // create thunks for the explicit parameters
                assert( appExpr->function->result );
                FunctionType *function = getFunctionType( appExpr->function->result );
                assert( function );
                std::list< DeclarationWithType* >::iterator formal;
                std::list< Expression* >::iterator actual;
                for ( formal = function->get_parameters().begin(), actual = appExpr->get_args().begin(); formal != function->get_parameters().end() && actual != appExpr->get_args().end(); ++formal, ++actual ) {
                        *actual = doSpecialization( (*formal)->get_type(), *actual, &appExpr->get_inferParams() );
                }
        }

        Expression * Specialize::postmutate( ApplicationExpr *appExpr ) {
                if ( ! InitTweak::isIntrinsicCallExpr( appExpr ) ) {
                        // create thunks for the inferred parameters
                        // don't need to do this for intrinsic calls, because they aren't actually passed
                        // need to handle explicit params before inferred params so that explicit params do not recieve a changed set of inferParams (and change them again)
                        // alternatively, if order starts to matter then copy appExpr's inferParams and pass them to handleExplicitParams.
                        handleExplicitParams( appExpr );
                        for ( InferredParams::iterator inferParam = appExpr->get_inferParams().begin(); inferParam != appExpr->get_inferParams().end(); ++inferParam ) {
                                inferParam->second.expr = doSpecialization( inferParam->second.formalType, inferParam->second.expr, inferParam->second.inferParams.get() );
                        }
                }
                return appExpr;
        }

        Expression * Specialize::postmutate( CastExpr *castExpr ) {
                if ( castExpr->result->isVoid() ) {
                        // can't specialize if we don't have a return value
                        return castExpr;
                }
                Expression *specialized = doSpecialization( castExpr->result, castExpr->arg, &castExpr->inferParams );
                if ( specialized != castExpr->arg ) {
                        // assume here that the specialization incorporates the cast
                        return specialized;
                } else {
                        return castExpr;
                }
        }

        void convertSpecializations( std::list< Declaration* >& translationUnit ) {
                PassVisitor<Specialize> spec;
                mutateAll( translationUnit, spec );
        }
} // namespace GenPoly

// Local Variables: //
// tab-width: 4 //
// mode: c++ //
// compile-command: "make install" //
// End: //