//
// 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.
//
// Lvalue.cc --
//
// Author           : Richard C. Bilson
// Created On       : Mon May 18 07:44:20 2015
// Last Modified By : Peter A. Buhr
// Last Modified On : Fri Mar 17 09:11:18 2017
// Update Count     : 5
//

#include <cassert>

#include "Lvalue.h"

#include "GenPoly.h"

#include "SynTree/Declaration.h"
#include "SynTree/Type.h"
#include "SynTree/Expression.h"
#include "SynTree/Statement.h"
#include "SynTree/Visitor.h"
#include "SynTree/Mutator.h"
#include "SymTab/Indexer.h"
#include "SymTab/Autogen.h"
#include "ResolvExpr/Resolver.h"
#include "ResolvExpr/typeops.h"

#include "Common/UniqueName.h"
#include "Common/utility.h"
#include "InitTweak/InitTweak.h"

#include "Common/PassVisitor.h"

// need to be careful about polymorphic references... e.g. in *? (___operator_deref__A0_1_0_0__Fd0_Pd0_intrinsic___1)
// the variable is automatically dereferenced and this causes errors dereferencing void*.

#if 0
#define PRINT(x) x
#else
#define PRINT(x)
#endif

namespace GenPoly {
	namespace {
		// TODO: fold this into the general createDeref function??
		Expression * mkDeref( Expression * arg ) {
			if ( SymTab::dereferenceOperator ) {
				VariableExpr * deref = new VariableExpr( SymTab::dereferenceOperator );
				deref->set_result( new PointerType( Type::Qualifiers(), deref->get_result() ) );
				Type * base = InitTweak::getPointerBase( arg->get_result() );
				assertf( base, "expected pointer type in dereference (type was %s)", toString( arg->get_result() ).c_str() );
				ApplicationExpr * ret = new ApplicationExpr( deref, { arg } );
				delete ret->get_result();
				ret->set_result( new ReferenceType( Type::Qualifiers(), base->clone() ) );
				return ret;
			} else {
				return UntypedExpr::createDeref( arg );
			}
		}

		struct ReferenceConversions final {
			Expression * postmutate( CastExpr * castExpr );
			Expression * postmutate( AddressExpr * addrExpr );
		};

		/// Intrinsic functions that take reference parameters don't REALLY take reference parameters -- their reference arguments must always be implicitly dereferenced.
		struct FixIntrinsicArgs final {
			Expression * postmutate( ApplicationExpr *appExpr );
		};


		/// Replace reference types with pointer types
		struct ReferenceTypeElimination final {
			Type * postmutate( ReferenceType * refType );
		};

		/// GCC-like Generalized Lvalues (which have since been removed from GCC)
		/// https://gcc.gnu.org/onlinedocs/gcc-3.4.6/gcc/Lvalues.html#Lvalues
		/// Replaces &(a,b) with (a, &b), &(a ? b : c) with (a ? &b : &c)
		struct GeneralizedLvalue final : public WithVisitorRef<GeneralizedLvalue> {
			Expression * postmutate( AddressExpr * addressExpr );
		};

		/// Removes redundant &*/*& pattern that this pass can generate
		struct CollapseAddrDeref final {
			Expression * postmutate( AddressExpr * addressExpr );
			Expression * postmutate( ApplicationExpr * appExpr );
		};
	} // namespace

	static bool referencesEliminated = false;
	// used by UntypedExpr::createDeref to determine whether result type of dereference should be ReferenceType or value type.
	bool referencesPermissable() {
		return ! referencesEliminated;
	}

	void convertLvalue( std::list< Declaration* >& translationUnit ) {
		std::cerr << "convertLvalue" << std::endl;
		PassVisitor<ReferenceConversions> refCvt;
		PassVisitor<ReferenceTypeElimination> elim;
		PassVisitor<GeneralizedLvalue> genLval;
		PassVisitor<FixIntrinsicArgs> fixer;
		PassVisitor<CollapseAddrDeref> collapser;
		mutateAll( translationUnit, refCvt );
		mutateAll( translationUnit, fixer );
		mutateAll( translationUnit, genLval );
		mutateAll( translationUnit, collapser );
		mutateAll( translationUnit, elim );  // last because other passes need reference types to work

		// from this point forward, no other pass should create reference types.
		referencesEliminated = true;
	}

	namespace {
		// true for intrinsic function calls that return a reference
		bool isIntrinsicReference( Expression * expr ) {
			if ( UntypedExpr * untyped = dynamic_cast< UntypedExpr * >( expr ) ) {
				std::string fname = InitTweak::getFunctionName( untyped );
				// known intrinsic-reference prelude functions
				return fname == "*?" || fname == "?[?]";
			} else if ( ApplicationExpr * appExpr = dynamic_cast< ApplicationExpr * > ( expr ) ) {
				if ( DeclarationWithType * func = InitTweak::getFunction( appExpr ) ) {
					// use type of return variable rather than expr result type, since it may have been changed to a pointer type
					FunctionType * ftype = GenPoly::getFunctionType( func->get_type() );
					Type * ret = ftype->get_returnVals().empty() ? nullptr : ftype->get_returnVals().front()->get_type();
					return func->get_linkage() == LinkageSpec::Intrinsic && dynamic_cast<ReferenceType *>( ret );
				}
			}
			return false;
		}

		// xxx - might need to & every * (or every * that is an arg to non-intrinsic function??)
		Expression * FixIntrinsicArgs::postmutate( ApplicationExpr * appExpr ) {
			// intrinsic functions don't really take reference-typed parameters, so they require an implicit dereference on their arguments.
			if ( DeclarationWithType * function = InitTweak::getFunction( appExpr ) ) {
				FunctionType * ftype = GenPoly::getFunctionType( function->get_type() );
				assertf( ftype, "Function declaration does not have function type." );
				// can be of differing lengths only when function is variadic
				assertf( ftype->get_parameters().size() == appExpr->get_args().size() || ftype->get_isVarArgs(), "ApplicationExpr args do not match formal parameter type." );

				if ( isIntrinsicReference( appExpr ) ) {
					// eliminate reference types from intrinsic applications - now they return lvalues
					appExpr->set_result( appExpr->get_result()->stripReferences() );
					appExpr->get_result()->set_lvalue( true );
				}

				unsigned int i = 0;
				const unsigned int end = ftype->get_parameters().size();
				for ( auto p : unsafe_group_iterate( appExpr->get_args(), ftype->get_parameters() ) ) {
					if (i == end) break;
					Expression *& arg = std::get<0>( p );
					Type * formal = std::get<1>( p )->get_type();
					PRINT(
						std::cerr << "pair<0>: " << arg << std::endl;
						std::cerr << "pair<1>: " << formal << std::endl;
					)
					if ( dynamic_cast<ReferenceType*>( formal ) ) {
						if ( isIntrinsicReference( arg ) ) {
							if ( function->get_linkage() != LinkageSpec::Intrinsic ) { // intrinsic functions that turn pointers into references
								// if argument is dereference or array subscript, the result isn't REALLY a reference, so it's not necessary to fix the argument
								PRINT( std::cerr << "is intrinsic arg in non-intrinsic call - adding address" << std::endl; )
								arg = new AddressExpr( arg );
							}
						} else if ( function->get_linkage() == LinkageSpec::Intrinsic ) {
							// if the parameter is a reference, add a dereference to the reference-typed argument.
							Type * baseType = InitTweak::getPointerBase( arg->get_result() );
							assertf( baseType, "parameter is reference, arg must be pointer or reference: %s", toString( arg->get_result() ) );
							PointerType * ptrType = new PointerType( Type::Qualifiers(), baseType->clone() );
							delete arg->get_result();
							arg->set_result( ptrType );
							arg = mkDeref( arg );
						}
					}
					++i;
				}
			}
			return appExpr;
		}

		Expression * ReferenceConversions::postmutate( AddressExpr * addrExpr ) {
			// Inner expression may have been lvalue to reference conversion, which becomes an address expression.
			// In this case, remove the outer address expression and return the argument.
			// TODO: It's possible that this might catch too much and require a more sophisticated check.
			if ( dynamic_cast<AddressExpr*>( addrExpr->get_arg() ) ) {
				Expression * arg = addrExpr->get_arg();
				arg->set_env( addrExpr->get_env() );
				addrExpr->set_arg( nullptr );
				addrExpr->set_env( nullptr );
				delete addrExpr;
				return arg;
			}
			return addrExpr;
		}

		Expression * ReferenceConversions::postmutate( CastExpr * castExpr ) {
			// xxx - is it possible to convert directly between reference types with a different base? E.g.,
			//   int x;
			//   (double&)x;
			// At the moment, I am working off of the assumption that this is illegal, thus the cast becomes redundant
			// after this pass, so trash the cast altogether. If that changes, care must be taken to insert the correct
			// pointer casts in the right places.

			// conversion to reference type
			if ( ReferenceType * refType = dynamic_cast< ReferenceType * >( castExpr->get_result() ) ) {
				(void)refType;
				if ( ReferenceType * otherRef = dynamic_cast< ReferenceType * >( castExpr->get_arg()->get_result() ) ) {
					// nothing to do if casting from reference to reference.
					(void)otherRef;
					PRINT( std::cerr << "convert reference to reference -- nop" << std::endl; )
					if ( isIntrinsicReference( castExpr->get_arg() ) ) {
						Expression * callExpr = castExpr->get_arg();
						PRINT(
							std::cerr << "but arg is deref -- &" << std::endl;
							std::cerr << callExpr << std::endl;
						)
						// move environment out to new top-level
						callExpr->set_env( castExpr->get_env() );
						castExpr->set_arg( nullptr );
						castExpr->set_env( nullptr );
						delete castExpr;
						return callExpr;
					}
					assertf( false, "non-intrinsic reference with cast of reference to reference not yet supported: ", toString( castExpr ) );
					PRINT( std::cerr << castExpr << std::endl; )
					return castExpr;
				} else if ( castExpr->get_arg()->get_result()->get_lvalue() ) {
					// conversion from lvalue to reference
					// xxx - keep cast, but turn into pointer cast??
					// xxx - memory
					PRINT(
						std::cerr << "convert lvalue to reference -- &" << std::endl;
						std::cerr << castExpr->get_arg() << std::endl;
					)
					AddressExpr * ret = new AddressExpr( castExpr->get_arg() );
					if ( refType->get_base()->get_qualifiers() != castExpr->get_arg()->get_result()->get_qualifiers() ) {
						// must keep cast if cast-to type is different from the actual type
						castExpr->set_arg( ret );

						return castExpr;
					}
					ret->set_env( castExpr->get_env() );
					castExpr->set_env( nullptr );
					castExpr->set_arg( nullptr );
					delete castExpr;
					return ret;
				} else {
					// rvalue to reference conversion -- introduce temporary
				}
				assertf( false, "Only conversions to reference from lvalue are currently supported: %s", toString( castExpr ).c_str() );
			} else if ( ReferenceType * refType = dynamic_cast< ReferenceType * >( castExpr->get_arg()->get_result() ) ) {
				(void)refType;
				// conversion from reference to rvalue
				PRINT(
					std::cerr << "convert reference to rvalue -- *" << std::endl;
					std::cerr << "was = " << castExpr << std::endl;
				)
				Expression * ret = castExpr->get_arg();
				TypeSubstitution * env = castExpr->get_env();
				castExpr->set_env( nullptr );
				if ( ! isIntrinsicReference( ret ) ) {
					// dereference if not already dereferenced
					ret = mkDeref( ret );
				}
				if ( ResolvExpr::typesCompatibleIgnoreQualifiers( castExpr->get_result(), castExpr->get_arg()->get_result()->stripReferences(), SymTab::Indexer() ) ) {
					// can remove cast if types are compatible, changing expression type to value type
					ret->set_result( castExpr->get_result()->clone() );
					castExpr->set_arg( nullptr );
					delete castExpr;
				} else {
					// must keep cast if types are different
					castExpr->set_arg( ret );
					ret = castExpr;
				}
				ret->set_env( env );
				PRINT( std::cerr << "now: " << ret << std::endl; )
				return ret;
			}
			return castExpr;
		}

		Type * ReferenceTypeElimination::postmutate( ReferenceType * refType ) {
			Type * base = refType->get_base();
			Type::Qualifiers qualifiers = refType->get_qualifiers();
			refType->set_base( nullptr );
			delete refType;
			return new PointerType( qualifiers, base );
		}

		Expression * GeneralizedLvalue::postmutate( AddressExpr * addrExpr ) {
			if ( CommaExpr * commaExpr = dynamic_cast< CommaExpr * >( addrExpr->get_arg() ) ) {
				Expression * arg1 = commaExpr->get_arg1()->clone();
				Expression * arg2 = commaExpr->get_arg2()->clone();
				delete addrExpr;
				return new CommaExpr( arg1, (new AddressExpr( arg2 ))->acceptMutator( *visitor ) );
			} else if ( ConditionalExpr * condExpr = dynamic_cast< ConditionalExpr * >( addrExpr->get_arg() ) ) {
				Expression * arg1 = condExpr->get_arg1()->clone();
				Expression * arg2 = condExpr->get_arg2()->clone();
				Expression * arg3 = condExpr->get_arg3()->clone();
				delete addrExpr;
				return new ConditionalExpr( arg1, (new AddressExpr( arg2 ))->acceptMutator( *visitor ), (new AddressExpr( arg3 ))->acceptMutator( *visitor ) );
			}
			return addrExpr;
		}

		Expression * CollapseAddrDeref::postmutate( AddressExpr * addressExpr ) {
			Expression * arg = addressExpr->get_arg();
			if ( isIntrinsicReference( arg ) ) {
				std::string fname = InitTweak::getFunctionName( arg );
				if ( fname == "*?" ) {
					Expression *& arg0 = InitTweak::getCallArg( arg, 0 );
					Expression * ret = arg0;
					ret->set_env( addressExpr->get_env() );
					arg0 = nullptr;
					addressExpr->set_env( nullptr );
					delete addressExpr;
					return ret;
				}
			}
			return addressExpr;
		}

		Expression * CollapseAddrDeref::postmutate( ApplicationExpr * appExpr ) {
			if ( isIntrinsicReference( appExpr ) ) {
				std::string fname = InitTweak::getFunctionName( appExpr );
				if ( fname == "*?" ) {
					Expression * arg = InitTweak::getCallArg( appExpr, 0 );
					// xxx - this isn't right, because it can remove casts that should be there...
					// while ( CastExpr * castExpr = dynamic_cast< CastExpr * >( arg ) ) {
					// 	arg = castExpr->get_arg();
					// }
					if ( AddressExpr * addrExpr = dynamic_cast< AddressExpr * >( arg ) ) {
						Expression * ret = addrExpr->get_arg();
						ret->set_env( appExpr->get_env() );
						addrExpr->set_arg( nullptr );
						appExpr->set_env( nullptr );
						delete appExpr;
						return ret;
					}
				}
			}
			return appExpr;
		}
	} // namespace
} // namespace GenPoly

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