source: src/ControlStruct/MLEMutator.cc @ 35f730f

//
// 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 : Peter A. Buhr
// Last Modified On : Thu Mar  8 17:08:25 2018
// Update Count     : 219
//

// 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
// It is unclear 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 <ext/alloc_traits.h>              // for __alloc_traits<>::value_type
#include <algorithm>                       // for find, find_if
#include <cassert>                         // for assert, assertf
#include <memory>                          // for allocator_traits<>::value_...

#include "Common/utility.h"                // for toString, operator+
#include "ControlStruct/LabelGenerator.h"  // for LabelGenerator
#include "MLEMutator.h"
#include "SynTree/Attribute.h"             // for Attribute
#include "SynTree/Expression.h"            // for Expression
#include "SynTree/Statement.h"             // for BranchStmt, CompoundStmt

namespace ControlStruct {
        MLEMutator::~MLEMutator() {
                delete targetTable;
                targetTable = 0;
        }
        namespace {
                bool isLoop( const MLEMutator::Entry & e ) { return dynamic_cast< WhileStmt * >( e.get_controlStructure() ) || dynamic_cast< ForStmt * >( e.get_controlStructure() ); }
                bool isSwitch( const MLEMutator::Entry & e ) { return dynamic_cast< SwitchStmt *>( e.get_controlStructure() ); }

                bool isBreakTarget( const MLEMutator::Entry & e ) { return isLoop( e ) || isSwitch( e ) || dynamic_cast< CompoundStmt *>( e.get_controlStructure() ); }
                bool isContinueTarget( const MLEMutator::Entry & e ) { return isLoop( e ); }
                bool isFallthroughTarget( const MLEMutator::Entry & e ) { return dynamic_cast< CaseStmt *>( e.get_controlStructure() );; }
                bool isFallthroughDefaultTarget( const MLEMutator::Entry & e ) { return isSwitch( e ); }
        } // namespace

        // 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, bool caseClause ) {
                SemanticErrorException errors;

                for ( std::list< Statement * >::iterator k = kids.begin(); k != kids.end(); k++ ) {
                        if ( caseClause ) {
                                // once a label is seen, it's no longer a valid fallthrough target
                                for ( Label & l : (*k)->labels ) {
                                        fallthroughLabels.erase( l );
                                }
                        }

                        // aggregate errors since the PassVisitor mutate loop was unrollled
                        try {
                                *k = (*k)->acceptMutator(*visitor);
                        } catch( SemanticErrorException &e ) {
                                errors.append( e );
                        }

                        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

                if ( ! errors.isEmpty() ) {
                        throw errors;
                }
        }

        void MLEMutator::premutate( CompoundStmt *cmpndStmt ) {
                visit_children = false;
                bool labeledBlock = !(cmpndStmt->labels.empty());
                if ( labeledBlock ) {
                        Label brkLabel = generator->newLabel("blockBreak", cmpndStmt);
                        enclosingControlStructures.push_back( Entry( cmpndStmt, brkLabel ) );
                        GuardAction( [this]() { enclosingControlStructures.pop_back(); } );
                } // if

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

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


        void addUnused( Statement * stmt, const Label & originalTarget ) {
                // break/continue without a label doesn't need unused attribute
                if ( originalTarget == "" ) return;
                // add unused attribute to the originalTarget of a labelled break/continue
                for ( Label & l : stmt->get_labels() ) {
                        // find the label to add unused attribute to
                        if ( l == originalTarget ) {
                                for ( Attribute * attr : l.get_attributes() ) {
                                        // ensure attribute isn't added twice
                                        if ( attr->get_name() == "unused" ) return;
                                }
                                l.get_attributes().push_back( new Attribute( "unused" ) );
                                return;
                        }
                }
                assertf( false, "Could not find label '%s' on statement %s", originalTarget.get_name().c_str(), toString( stmt ).c_str() );
        }


        Statement *MLEMutator::postmutate( BranchStmt *branchStmt ) throw ( SemanticErrorException ) {
                std::string originalTarget = branchStmt->originalTarget;

                std::list< Entry >::reverse_iterator targetEntry;
                switch ( branchStmt->get_type() ) {
                        case BranchStmt::Goto:
                                return branchStmt;
                        case BranchStmt::Continue:
                        case BranchStmt::Break: {
                                bool isContinue = branchStmt->get_type() == BranchStmt::Continue;
                                // unlabeled break/continue
                                if ( branchStmt->get_target() == "" ) {
                                        if ( isContinue ) {
                                                // continue target is outermost loop
                                                targetEntry = std::find_if( enclosingControlStructures.rbegin(), enclosingControlStructures.rend(), isContinueTarget );
                                        } else {
                                                // break target is outermost loop, switch, or block control structure
                                                if ( enclosingControlStructures.empty() ) SemanticError( branchStmt->location, "'break' outside a loop, 'switch', or labelled block" );
                                                targetEntry = std::find_if( enclosingControlStructures.rbegin(), enclosingControlStructures.rend(), isBreakTarget );
                                        } // if
                                } else {
                                        // labeled break/continue - lookup label in table to find attached control structure
                                        targetEntry = std::find( enclosingControlStructures.rbegin(), enclosingControlStructures.rend(), (*targetTable)[branchStmt->get_target()] );
                                } // if
                                // ensure that selected target is valid
                                if ( targetEntry == enclosingControlStructures.rend() || (isContinue && ! isContinueTarget( *targetEntry ) ) ) {
                                        SemanticError( branchStmt->location, toString( (isContinue ? "'continue'" : "'break'"), " target must be an enclosing ", (isContinue ? "loop: " : "control structure: "), originalTarget ) );
                                } // if
                                break;
                        }
                        case BranchStmt::FallThrough:
                                targetEntry = std::find_if( enclosingControlStructures.rbegin(), enclosingControlStructures.rend(), isFallthroughTarget );
                                // ensure that selected target is valid
                                if ( targetEntry == enclosingControlStructures.rend() ) {
                                        SemanticError( branchStmt->location, "'fallthrough' must be enclosed in a 'switch' or 'choose'" );
                                } // if
                                if ( branchStmt->get_target() != "" ) {
                                        // labelled fallthrough
                                        // target must be in the set of valid fallthrough labels
                                        if ( ! fallthroughLabels.count( branchStmt->get_target() ) ) {
                                                SemanticError( branchStmt->location, toString( "'fallthrough' target must be a later case statement: ", originalTarget ) );
                                        }
                                        return new BranchStmt( originalTarget, BranchStmt::Goto );
                                }
                                break;
                        case BranchStmt::FallThroughDefault: {
                                // fallthrough default
                                targetEntry = std::find_if( enclosingControlStructures.rbegin(), enclosingControlStructures.rend(), isFallthroughDefaultTarget );

                                // ensure that fallthrough is within a switch or choose
                                if ( targetEntry == enclosingControlStructures.rend() ) {
                                        SemanticError( branchStmt->location, "'fallthrough' must be enclosed in a 'switch' or 'choose'" );
                                } // if

                                // ensure that switch or choose has a default clause
                                SwitchStmt * switchStmt = strict_dynamic_cast< SwitchStmt * >( targetEntry->get_controlStructure() );
                                bool foundDefault = false;
                                for ( Statement * stmt : switchStmt->statements ) {
                                        CaseStmt * caseStmt = strict_dynamic_cast< CaseStmt * >( stmt );
                                        if ( caseStmt->isDefault() ) {
                                                foundDefault = true;
                                        } // if
                                } // for
                                if ( ! foundDefault ) {
                                        SemanticError( branchStmt->location, "'fallthrough default' must be enclosed in a 'switch' or 'choose' control structure with a 'default' clause" );
                                }
                                break;
                        }

                        default:
                                assert( false );
                } // switch

                // branch error checks, get the appropriate label name and create a goto
                Label exitLabel;
                switch ( branchStmt->type ) {
                  case BranchStmt::Break:
                                assert( targetEntry->useBreakExit() != "");
                                exitLabel = targetEntry->useBreakExit();
                                break;
                  case BranchStmt::Continue:
                                assert( targetEntry->useContExit() != "");
                                exitLabel = targetEntry->useContExit();
                                break;
                  case BranchStmt::FallThrough:
                                assert( targetEntry->useFallExit() != "");
                                exitLabel = targetEntry->useFallExit();
                                break;
                  case BranchStmt::FallThroughDefault:
                                assert( targetEntry->useFallDefaultExit() != "");
                                exitLabel = targetEntry->useFallDefaultExit();
                                // check that fallthrough default comes before the default clause
                                if ( ! targetEntry->isFallDefaultValid() ) {
                                        SemanticError( branchStmt->location, "'fallthrough default' must precede the 'default' clause" );
                                }
                                break;
                  default:
                                assert(0);                                      // shouldn't be here
                } // switch

                // add unused attribute to label to silence warnings
                addUnused( targetEntry->get_controlStructure(), branchStmt->originalTarget );

                // transform break/continue statements into goto to simplify later handling of branches
                delete branchStmt;
                return new BranchStmt( 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();
                        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

                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() );
                } // if

                return newBody;
        }

        template< typename LoopClass >
        void MLEMutator::prehandleLoopStmt( 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", loopStmt);
                Label contLabel = generator->newLabel("loopContinue", loopStmt);
                enclosingControlStructures.push_back( Entry( loopStmt, brkLabel, contLabel ) );
                GuardAction( [this]() { enclosingControlStructures.pop_back(); } );
        }

        template< typename LoopClass >
        Statement * MLEMutator::posthandleLoopStmt( LoopClass * loopStmt ) {
                assert( ! enclosingControlStructures.empty() );
                Entry &e = enclosingControlStructures.back();
                // sanity check that the enclosing loops have been popped correctly
                assert ( e == loopStmt );

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

        void MLEMutator::premutate( WhileStmt * whileStmt ) {
                return prehandleLoopStmt( whileStmt );
        }

        void MLEMutator::premutate( ForStmt * forStmt ) {
                return prehandleLoopStmt( forStmt );
        }

        Statement * MLEMutator::postmutate( WhileStmt * whileStmt ) {
                return posthandleLoopStmt( whileStmt );
        }

        Statement * MLEMutator::postmutate( ForStmt * forStmt ) {
                return posthandleLoopStmt( forStmt );
        }

        void MLEMutator::premutate( IfStmt * ifStmt ) {
                // generate a label for breaking out of a labeled if
                bool labeledBlock = !(ifStmt->get_labels().empty());
                if ( labeledBlock ) {
                        Label brkLabel = generator->newLabel("blockBreak", ifStmt);
                        enclosingControlStructures.push_back( Entry( ifStmt, brkLabel ) );
                        GuardAction( [this]() { enclosingControlStructures.pop_back(); } );
                } // if
        }

        Statement * MLEMutator::postmutate( IfStmt * ifStmt ) {
                bool labeledBlock = !(ifStmt->get_labels().empty());
                if ( labeledBlock ) {
                        if ( ! enclosingControlStructures.back().useBreakExit().empty() ) {
                                set_breakLabel( enclosingControlStructures.back().useBreakExit() );
                        } // if
                } // if
                return ifStmt;
        }

        void MLEMutator::premutate( CaseStmt *caseStmt ) {
                visit_children = false;

                // mark default as seen before visiting its statements to catch default loops
                if ( caseStmt->isDefault() ) {
                        enclosingControlStructures.back().seenDefault();
                } // if

                caseStmt->condition = maybeMutate( caseStmt->condition, *visitor );
                Label fallLabel = generator->newLabel( "fallThrough", caseStmt );
                {
                        // ensure that stack isn't corrupted by exceptions in fixBlock
                        auto guard = makeFuncGuard( [&]() { enclosingControlStructures.push_back( Entry( caseStmt, fallLabel ) ); }, [this]() { enclosingControlStructures.pop_back(); } );

                        // empty case statement
                        if( ! caseStmt->stmts.empty() ) {
                                // the parser ensures that all statements in a case are grouped into a block
                                CompoundStmt * block = strict_dynamic_cast< CompoundStmt * >( caseStmt->stmts.front() );
                                fixBlock( block->kids, true );

                                // add fallthrough label if necessary
                                assert( ! enclosingControlStructures.empty() );
                                if ( enclosingControlStructures.back().isFallUsed() ) {
                                        std::list<Label> ls{ enclosingControlStructures.back().useFallExit() };
                                        caseStmt->stmts.push_back( new NullStmt( ls ) );
                                } // if
                        } // if
                }
                assert( ! enclosingControlStructures.empty() );
                assertf( dynamic_cast<SwitchStmt *>( enclosingControlStructures.back().get_controlStructure() ), "Control structure enclosing a case clause must be a switch, but is: %s", toCString( enclosingControlStructures.back().get_controlStructure() ) );
                if ( caseStmt->isDefault() ) {
                        if ( enclosingControlStructures.back().isFallDefaultUsed() ) {
                                // add fallthrough default label if necessary
                                std::list<Label> ls{ enclosingControlStructures.back().useFallDefaultExit() };
                                caseStmt->stmts.push_front( new NullStmt( ls ) );
                        } // if
                } // if
        }

        void MLEMutator::premutate( SwitchStmt *switchStmt ) {
                // generate a label for breaking out of a labeled switch
                Label brkLabel = generator->newLabel("switchBreak", switchStmt);
                auto it = std::find_if( switchStmt->statements.rbegin(), switchStmt->statements.rend(), [](Statement * stmt) {
                        CaseStmt * caseStmt = strict_dynamic_cast< CaseStmt * >( stmt );
                        return caseStmt->isDefault();
                });
                CaseStmt * defaultCase = it != switchStmt->statements.rend() ? strict_dynamic_cast<CaseStmt *>( *it ) : nullptr;
                Label fallDefaultLabel = defaultCase ? generator->newLabel( "fallThroughDefault", defaultCase ) : "";
                enclosingControlStructures.push_back( Entry(switchStmt, brkLabel, fallDefaultLabel) );
                GuardAction( [this]() { enclosingControlStructures.pop_back(); } );

                // Collect valid labels for fallthrough. This is initially all labels at the same level as a case statement.
                // As labels are seen during traversal, they are removed, since fallthrough is not allowed to jump backwards.
                for ( Statement * stmt : switchStmt->statements ) {
                        CaseStmt * caseStmt = strict_dynamic_cast< CaseStmt * >( stmt );
                        if ( caseStmt->stmts.empty() ) continue;
                        CompoundStmt * block = dynamic_cast< CompoundStmt * >( caseStmt->stmts.front() );
                        for ( Statement * stmt : block->kids ) {
                                for ( Label & l : stmt->labels ) {
                                        fallthroughLabels.insert( l );
                                }
                        }
                }
        }

        Statement * MLEMutator::postmutate( SwitchStmt * switchStmt ) {
                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 * > &statements = switchStmt->statements;
                        if ( statements.empty() ) {
                                statements.push_back( CaseStmt::makeDefault() );
                        } // if

                        if ( CaseStmt * c = dynamic_cast< CaseStmt * >( statements.back() ) ) {
                                Statement * stmt = new BranchStmt( Label("brkLabel"), BranchStmt::Break );
                                stmt->labels.push_back( e.useBreakExit() );
                                c->stmts.push_back( stmt );
                        } else assert(0); // as of this point, all statements of a switch are still CaseStmts
                } // if

                assert ( enclosingControlStructures.back() == switchStmt );
                return switchStmt;
        }
} // namespace ControlStruct

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