source: src/ControlStruct/MLEMutator.cc @ 3a808fd

//
// 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.
//
// MLEMutator.cc --
//
// Author           : Rodolfo G. Esteves
// Created On       : Mon May 18 07:44:20 2015
// Last Modified By : Rob Schluntz
// Last Modified On : Mon Jul 20 13:58:35 2015
// Update Count     : 176
//

// NOTE: There are two known subtle differences from the code that uC++
// generates for the same input
// -CFA puts the break label inside at the end of a switch, uC++ puts it after
// -CFA puts the break label after a block, uC++ puts it inside at the end
// we don't yet know if these differences are important, but if they are then
// the fix would go in this file, since this is where these labels are generated.

#include <cassert>
#include <algorithm>

#include "MLEMutator.h"
#include "SynTree/Statement.h"
#include "SynTree/Expression.h"
#include "SynTree/Attribute.h"

namespace ControlStruct {
        MLEMutator::~MLEMutator() {
                delete targetTable;
                targetTable = 0;
        }
        namespace {
                Statement * isLoop( Statement * stmt ) { return dynamic_cast< WhileStmt * >( stmt ) ? stmt : dynamic_cast< ForStmt * >( stmt ) ? stmt : 0; }
        }

        // break labels have to come after the statement they break out of,
        // so mutate a statement, then if they inform us through the breakLabel field
        // tha they need a place to jump to on a break statement, add the break label
        // to the body of statements
        void MLEMutator::fixBlock( std::list< Statement * > &kids ) {
                for ( std::list< Statement * >::iterator k = kids.begin(); k != kids.end(); k++ ) {
                        *k = (*k)->acceptMutator(*this);

                        if ( ! get_breakLabel().empty() ) {
                                std::list< Statement * >::iterator next = k+1;
                                std::list<Label> ls; ls.push_back( get_breakLabel() );
                                kids.insert( next, new NullStmt( ls ) );
                                set_breakLabel("");
                        } // if
                } // for
        }

        CompoundStmt* MLEMutator::mutate( CompoundStmt *cmpndStmt ) {
                bool labeledBlock = !(cmpndStmt->get_labels().empty());
                if ( labeledBlock ) {
                        Label brkLabel = generator->newLabel("blockBreak");
                        enclosingControlStructures.push_back( Entry( cmpndStmt, brkLabel ) );
                } // if

                // a child statement may set the break label
                // - if they do, attach it to the next statement
                std::list< Statement * > &kids = cmpndStmt->get_kids();
                fixBlock( kids );

                if ( labeledBlock ) {
                        assert( ! enclosingControlStructures.empty() );
                        if ( ! enclosingControlStructures.back().useBreakExit().empty() ) {
                                set_breakLabel( enclosingControlStructures.back().useBreakExit() );
                        }
                        enclosingControlStructures.pop_back();
                } // if

                return cmpndStmt;
        }

        template< typename LoopClass >
        Statement *MLEMutator::handleLoopStmt( LoopClass *loopStmt ) {
                // remember this as the most recent enclosing loop, then mutate
                // the body of the loop -- this will determine whether brkLabel
                // and contLabel are used with branch statements
                // and will recursively do the same to nested loops
                Label brkLabel = generator->newLabel("loopBreak");
                Label contLabel = generator->newLabel("loopContinue");
                enclosingControlStructures.push_back( Entry( loopStmt, brkLabel, contLabel ) );
                loopStmt->set_body ( loopStmt->get_body()->acceptMutator( *this ) );

                // sanity check that the enclosing loops have been popped correctly
                Entry &e = enclosingControlStructures.back();
                assert ( e == loopStmt );

                // this will take the necessary steps to add definitions of the previous
                // two labels, if they are used.
                loopStmt->set_body( mutateLoop( loopStmt->get_body(), e ) );
                enclosingControlStructures.pop_back();

                return loopStmt;
        }

        Statement *MLEMutator::mutate( CaseStmt *caseStmt ) {
                caseStmt->set_condition( maybeMutate( caseStmt->get_condition(), *this ) );
                fixBlock( caseStmt->get_statements() );

                return caseStmt;
        }

        template< typename SwitchClass >
        Statement *MLEMutator::handleSwitchStmt( SwitchClass *switchStmt ) {
                // generate a label for breaking out of a labeled switch
                Label brkLabel = generator->newLabel("switchBreak");
                enclosingControlStructures.push_back( Entry(switchStmt, brkLabel) );
                mutateAll( switchStmt->get_branches(), *this );

                Entry &e = enclosingControlStructures.back();
                assert ( e == switchStmt );

                // only generate break label if labeled break is used
                if (e.isBreakUsed()) {
                        // for the purposes of keeping switch statements uniform (i.e. all statements that are
                        // direct children of a switch should be CastStmts), append the exit label + break to the
                        // last case statement; create a default case if there are no cases
                        std::list< Statement * > &branches = switchStmt->get_branches();
                        if ( branches.empty() ) {
                                branches.push_back( CaseStmt::makeDefault() );
                        }

                        if ( CaseStmt * c = dynamic_cast< CaseStmt * >( branches.back() ) ) {
                                std::list<Label> temp; temp.push_back( brkLabel );
                                c->get_statements().push_back( new BranchStmt( temp, Label("brkLabel"), BranchStmt::Break ) );
                        } else assert(0); // as of this point, all branches of a switch are still CaseStmts
                }

                assert ( enclosingControlStructures.back() == switchStmt );
                enclosingControlStructures.pop_back();
                return switchStmt;
        }

        Statement *MLEMutator::mutate( BranchStmt *branchStmt ) throw ( SemanticError ) {
                std::string originalTarget = branchStmt->get_originalTarget();

                std::list< Entry >::reverse_iterator targetEntry;
                if ( branchStmt->get_type() == BranchStmt::Goto ) {
                        return branchStmt;
                } else if ( branchStmt->get_type() == BranchStmt::Continue) {
                        // continue target must be a loop
                        if ( branchStmt->get_target() == "" ) {
                                targetEntry = std::find_if( enclosingControlStructures.rbegin(), enclosingControlStructures.rend(), [](Entry &e) { return isLoop( e.get_controlStructure() ); } );
                        } else {
                                // labelled continue - lookup label in table ot find attached control structure
                                targetEntry = std::find( enclosingControlStructures.rbegin(), enclosingControlStructures.rend(), (*targetTable)[branchStmt->get_target()] );
                        }
                        if ( targetEntry == enclosingControlStructures.rend() || ! isLoop( targetEntry->get_controlStructure() ) ) {
                                throw SemanticError( "'continue' target must be an enclosing loop: " + originalTarget );
                        }
                } else if ( branchStmt->get_type() == BranchStmt::Break ) {
                        if ( enclosingControlStructures.empty() ) throw SemanticError( "'break' outside a loop, switch, or labelled block" );
                        targetEntry = enclosingControlStructures.rbegin();
                } else {
                        assert( false );
                }

                if ( branchStmt->get_target() != "" && targetTable->find( branchStmt->get_target() ) == targetTable->end() ) {
                        throw SemanticError("The label defined in the exit loop statement does not exist: " + originalTarget );  // shouldn't happen (since that's already checked)
                }

                // branch error checks, get the appropriate label name and create a goto
                Label exitLabel;
                switch ( branchStmt->get_type() ) {
                  case BranchStmt::Break:
                                assert( targetEntry->useBreakExit() != "");
                                exitLabel = targetEntry->useBreakExit();
                                break;
                  case BranchStmt::Continue:
                                assert( targetEntry->useContExit() != "");
                                exitLabel = targetEntry->useContExit();
                                break;
                  default:
                                assert(0);                                      // shouldn't be here
                } // switch

                if ( branchStmt->get_target() == "" && branchStmt->get_type() != BranchStmt::Continue ) {
                        // unlabelled break/continue - can keep branch as break/continue for extra semantic information, but add
                        // exitLabel as its destination so that label passes can easily determine where the break/continue goes to
                        branchStmt->set_target( exitLabel );
                        return branchStmt;
                } else {
                        // labelled break/continue - can't easily emulate this with break and continue, so transform into a goto
                        delete branchStmt;
                        return new BranchStmt( std::list<Label>(), exitLabel, BranchStmt::Goto );
                }
        }

        Statement *MLEMutator::mutateLoop( Statement *bodyLoop, Entry &e ) {
                // ensure loop body is a block
                CompoundStmt *newBody;
                if ( ! (newBody = dynamic_cast<CompoundStmt *>( bodyLoop )) ) {
                        newBody = new CompoundStmt( std::list< Label >() );
                        newBody->get_kids().push_back( bodyLoop );
                } // if

                // only generate these when needed

                if ( e.isContUsed() ) {
                        // continue label goes in the body as the last statement
                        std::list< Label > labels; labels.push_back( e.useContExit() );
                        newBody->get_kids().push_back( new NullStmt( labels ) );
                }

                if ( e.isBreakUsed() ) {
                        // break label goes after the loop -- it'll get set by the
                        // outer mutator if we do this
                        set_breakLabel( e.useBreakExit() );
                }

                return newBody;
        }

        Statement *MLEMutator::mutate( WhileStmt *whileStmt ) {
                return handleLoopStmt( whileStmt );
        }

        Statement *MLEMutator::mutate( ForStmt *forStmt ) {
                return handleLoopStmt( forStmt );
        }

        Statement *MLEMutator::mutate( SwitchStmt *switchStmt ) {
                return handleSwitchStmt( switchStmt );
        }

        Statement *MLEMutator::mutate( ChooseStmt *switchStmt ) {
                return handleSwitchStmt( switchStmt );
        }

} // namespace ControlStruct

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