source: src/ControlStruct/MultiLevelExit.cpp@ fc72696c

//
// 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.
//
// MultiLevelExit.cpp -- Replaces CFA's local control flow with C's versions.
//
// Author           : Andrew Beach
// Created On       : Mon Nov  1 13:48:00 2021
// Last Modified By : Peter A. Buhr
// Last Modified On : Mon Jan 31 22:35:08 2022
// Update Count     : 28
//

#include "MultiLevelExit.hpp"

#include "AST/Pass.hpp"
#include "AST/Stmt.hpp"
#include "LabelGeneratorNew.hpp"

#include <set>
using namespace std;
using namespace ast;

namespace ControlStruct {
class Entry {
  public:
        const Stmt * stmt;
  private:
        // Organized like a manual ADT. Avoids creating a bunch of dead data.
        struct Target {
                Label label;
                bool used = false;
                Target( const Label & label ) : label( label ) {}
                Target() : label( CodeLocation() ) {}
        };
        Target firstTarget;
        Target secondTarget;

        enum Kind {
                ForStmtK, WhileStmtK, CompoundStmtK, IfStmtK, CaseStmtK, SwitchStmtK, TryStmtK
        } kind;

        bool fallDefaultValid = true;

        static Label & useTarget( Target & target ) {
                target.used = true;
                return target.label;
        }

  public:
        Entry( const ForStmt * stmt, Label breakExit, Label contExit ) :
                stmt( stmt ), firstTarget( breakExit ), secondTarget( contExit ), kind( ForStmtK ) {}
        Entry( const WhileStmt * stmt, Label breakExit, Label contExit ) :
                stmt( stmt ), firstTarget( breakExit ), secondTarget( contExit ), kind( WhileStmtK ) {}
        Entry( const CompoundStmt *stmt, Label breakExit ) :
                stmt( stmt ), firstTarget( breakExit ), secondTarget(), kind( CompoundStmtK ) {}
        Entry( const IfStmt *stmt, Label breakExit ) :
                stmt( stmt ), firstTarget( breakExit ), secondTarget(), kind( IfStmtK ) {}
        Entry( const CaseStmt *stmt, Label fallExit ) :
                stmt( stmt ), firstTarget( fallExit ), secondTarget(), kind( CaseStmtK ) {}
        Entry( const SwitchStmt *stmt, Label breakExit, Label fallDefaultExit ) :
                stmt( stmt ), firstTarget( breakExit ), secondTarget( fallDefaultExit ), kind( SwitchStmtK ) {}
        Entry( const TryStmt *stmt, Label breakExit ) :
                stmt( stmt ), firstTarget( breakExit ), secondTarget(), kind( TryStmtK ) {}

        bool isContTarget() const { return kind <= WhileStmtK; }
        bool isBreakTarget() const { return kind != CaseStmtK; }
        bool isFallTarget() const { return kind == CaseStmtK; }
        bool isFallDefaultTarget() const { return kind == SwitchStmtK; }

        Label useContExit() { assert( kind <= WhileStmtK ); return useTarget(secondTarget); }
        Label useBreakExit() { assert( kind != CaseStmtK ); return useTarget(firstTarget); }
        Label useFallExit() { assert( kind == CaseStmtK );  return useTarget(firstTarget); }
        Label useFallDefaultExit() { assert( kind == SwitchStmtK ); return useTarget(secondTarget); }

        bool isContUsed() const { assert( kind <= WhileStmtK ); return secondTarget.used; }
        bool isBreakUsed() const { assert( kind != CaseStmtK ); return firstTarget.used; }
        bool isFallUsed() const { assert( kind == CaseStmtK ); return firstTarget.used; }
        bool isFallDefaultUsed() const { assert( kind == SwitchStmtK ); return secondTarget.used; }
        void seenDefault() { fallDefaultValid = false; }
        bool isFallDefaultValid() const { return fallDefaultValid; }
};

// Helper predicates used in find_if calls (it doesn't take methods):
bool isBreakTarget( const Entry & entry ) {
        return entry.isBreakTarget();
}

bool isContinueTarget( const Entry & entry ) {
        return entry.isContTarget();
}

bool isFallthroughTarget( const Entry & entry ) {
        return entry.isFallTarget();
}

bool isFallthroughDefaultTarget( const Entry & entry ) {
        return entry.isFallDefaultTarget();
}

struct MultiLevelExitCore final :
        public WithVisitorRef<MultiLevelExitCore>,
        public WithShortCircuiting, public WithGuards {
        MultiLevelExitCore( const LabelToStmt & lt );

        void previsit( const FunctionDecl * );

        const CompoundStmt * previsit( const CompoundStmt * );
        const BranchStmt * postvisit( const BranchStmt * );
        void previsit( const WhileStmt * );
        const WhileStmt * postvisit( const WhileStmt * );
        void previsit( const ForStmt * );
        const ForStmt * postvisit( const ForStmt * );
        const CaseStmt * previsit( const CaseStmt * );
        void previsit( const IfStmt * );
        const IfStmt * postvisit( const IfStmt * );
        void previsit( const SwitchStmt * );
        const SwitchStmt * postvisit( const SwitchStmt * );
        void previsit( const ReturnStmt * );
        void previsit( const TryStmt * );
        void postvisit( const TryStmt * );
        void previsit( const FinallyStmt * );

        const Stmt * mutateLoop( const Stmt * body, Entry& );

        const LabelToStmt & target_table;
        set<Label> fallthrough_labels;
        vector<Entry> enclosing_control_structures;
        Label break_label;
        bool inFinally;

        template<typename LoopNode>
        void prehandleLoopStmt( const LoopNode * loopStmt );
        template<typename LoopNode>
        const LoopNode * posthandleLoopStmt( const LoopNode * loopStmt );

        list<ptr<Stmt>> fixBlock(
                const list<ptr<Stmt>> & kids, bool caseClause );

        template<typename UnaryPredicate>
        auto findEnclosingControlStructure( UnaryPredicate pred ) {
                return find_if( enclosing_control_structures.rbegin(),
                                                enclosing_control_structures.rend(), pred );
        }
};

NullStmt * labelledNullStmt(
        const CodeLocation & cl, const Label & label ) {
        return new NullStmt( cl, vector<Label>{ label } );
}

MultiLevelExitCore::MultiLevelExitCore( const LabelToStmt & lt ) :
        target_table( lt ), break_label( CodeLocation(), "" ),
        inFinally( false )
{}

void MultiLevelExitCore::previsit( const FunctionDecl * ) {
        visit_children = false;
}

const CompoundStmt * MultiLevelExitCore::previsit(
        const CompoundStmt * stmt ) {
        visit_children = false;
        bool isLabeled = !stmt->labels.empty();
        if ( isLabeled ) {
                Label breakLabel = newLabel( "blockBreak", stmt );
                enclosing_control_structures.emplace_back( stmt, breakLabel );
                GuardAction( [this]() { enclosing_control_structures.pop_back(); } );
        }

        auto mutStmt = mutate( stmt );
        // A child statement may set the break label.
        mutStmt->kids = move( fixBlock( stmt->kids, false ) );

        if ( isLabeled ) {
                assert( !enclosing_control_structures.empty() );
                Entry & entry = enclosing_control_structures.back();
                if ( !entry.useBreakExit().empty() ) {
                        break_label = entry.useBreakExit();
                }
        }
        return mutStmt;
}

size_t getUnusedIndex(
        const Stmt * stmt, const Label & originalTarget ) {
        const size_t size = stmt->labels.size();

        // If the label is empty, do not add unused attribute.
  if ( originalTarget.empty() ) return size;

        // Search for a label that matches the originalTarget.
        for ( size_t i = 0 ; i < size ; ++i ) {
                const Label & label = stmt->labels[i];
                if ( label == originalTarget ) {
                        for ( const Attribute * attr : label.attributes ) {
                                if ( attr->name == "unused" ) return size;
                        }
                        return i;
                }
        }
        assertf( false, "Could not find label '%s' on statement %s",
                         originalTarget.name.c_str(), toString( stmt ).c_str() );
}

const Stmt * addUnused(
        const Stmt * stmt, const Label & originalTarget ) {
        size_t i = getUnusedIndex( stmt, originalTarget );
        if ( i == stmt->labels.size() ) {
                return stmt;
        }
        Stmt * mutStmt = mutate( stmt );
        mutStmt->labels[i].attributes.push_back( new Attribute( "unused" ) );
        return mutStmt;
}

const BranchStmt * MultiLevelExitCore::postvisit( const BranchStmt * stmt ) {
        vector<Entry>::reverse_iterator targetEntry =
                enclosing_control_structures.rend();
        switch ( stmt->kind ) {
          case BranchStmt::Goto:
                return stmt;
          case BranchStmt::Continue:
          case BranchStmt::Break: {
                  bool isContinue = stmt->kind == BranchStmt::Continue;
                  // Handle unlabeled break and continue.
                  if ( stmt->target.empty() ) {
                          if ( isContinue ) {
                                  targetEntry = findEnclosingControlStructure( isContinueTarget );
                          } else {
                                  if ( enclosing_control_structures.empty() ) {
                                          SemanticError( stmt->location,
                                                                         "'break' outside a loop, 'switch', or labelled block" );
                                  }
                                  targetEntry = findEnclosingControlStructure( isBreakTarget );
                          }
                          // Handle labeled break and continue.
                  } else {
                          // Lookup label in table to find attached control structure.
                          targetEntry = findEnclosingControlStructure(
                                  [ targetStmt = target_table.at(stmt->target) ](auto entry){
                                          return entry.stmt == targetStmt;
                                  } );
                  }
                  // Ensure that selected target is valid.
                  if ( targetEntry == enclosing_control_structures.rend() || ( isContinue && !isContinueTarget( *targetEntry ) ) ) {
                          SemanticError( stmt->location, toString( (isContinue ? "'continue'" : "'break'"),
                                                        " target must be an enclosing ", (isContinue ? "loop: " : "control structure: "),
                                                        stmt->originalTarget ) );
                  }
                  break;
          }
          case BranchStmt::FallThrough: {
                  targetEntry = findEnclosingControlStructure( isFallthroughTarget );
                  // Check that target is valid.
                  if ( targetEntry == enclosing_control_structures.rend() ) {
                          SemanticError( stmt->location, "'fallthrough' must be enclosed in a 'switch' or 'choose'" );
                  }
                  if ( !stmt->target.empty() ) {
                          // Labelled fallthrough: target must be a valid fallthough label.
                          if ( !fallthrough_labels.count( stmt->target ) ) {
                                  SemanticError( stmt->location, toString( "'fallthrough' target must be a later case statement: ",
                                                                                                                   stmt->originalTarget ) );
                          }
                          return new BranchStmt(
                                  stmt->location, BranchStmt::Goto, stmt->originalTarget );
                  }
                  break;
          }
          case BranchStmt::FallThroughDefault: {
                  targetEntry = findEnclosingControlStructure( isFallthroughDefaultTarget );

                  // Check if in switch or choose statement.
                  if ( targetEntry == enclosing_control_structures.rend() ) {
                          SemanticError( stmt->location, "'fallthrough' must be enclosed in a 'switch' or 'choose'" );
                  }

                  // Check if switch or choose has default clause.
                  auto switchStmt = strict_dynamic_cast< const SwitchStmt * >( targetEntry->stmt );
                  bool foundDefault = false;
                  for ( auto subStmt : switchStmt->stmts ) {
                          const CaseStmt * caseStmt = subStmt.strict_as<CaseStmt>();
                          if ( caseStmt->isDefault() ) {
                                  foundDefault = true;
                                  break;
                          }
                  }
                  if ( ! foundDefault ) {
                          SemanticError( stmt->location, "'fallthrough default' must be enclosed in a 'switch' or 'choose'"
                                                         "control structure with a 'default' clause" );
                  }
                  break;
          }
          default:
                assert( false );
        }

        // Branch error checks: get the appropriate label name:
        // (This label is always replaced.)
        Label exitLabel( CodeLocation(), "" );
        switch ( stmt->kind ) {
          case BranchStmt::Break:
                assert( !targetEntry->useBreakExit().empty() );
                exitLabel = targetEntry->useBreakExit();
                break;
          case BranchStmt::Continue:
                assert( !targetEntry->useContExit().empty() );
                exitLabel = targetEntry->useContExit();
                break;
          case BranchStmt::FallThrough:
                assert( !targetEntry->useFallExit().empty() );
                exitLabel = targetEntry->useFallExit();
                break;
          case BranchStmt::FallThroughDefault:
                assert( !targetEntry->useFallDefaultExit().empty() );
                exitLabel = targetEntry->useFallDefaultExit();
                // Check that fallthrough default comes before the default clause.
                if ( !targetEntry->isFallDefaultValid() ) {
                        SemanticError( stmt->location, "'fallthrough default' must precede the 'default' clause" );
                }
                break;
          default:
                assert(0);
        }

        // Add unused attribute to silence warnings.
        targetEntry->stmt = addUnused( targetEntry->stmt, stmt->originalTarget );

        // Replace with goto to make later passes more uniform.
        return new BranchStmt( stmt->location, BranchStmt::Goto, exitLabel );
}

void MultiLevelExitCore::previsit( const WhileStmt * stmt ) {
        return prehandleLoopStmt( stmt );
}

const WhileStmt * MultiLevelExitCore::postvisit( const WhileStmt * stmt ) {
        return posthandleLoopStmt( stmt );
}

void MultiLevelExitCore::previsit( const ForStmt * stmt ) {
        return prehandleLoopStmt( stmt );
}

const ForStmt * MultiLevelExitCore::postvisit( const ForStmt * stmt ) {
        return posthandleLoopStmt( stmt );
}

// Mimic what the built-in push_front would do anyways. It is O(n).
void push_front(
        vector<ptr<Stmt>> & vec, const Stmt * element ) {
        vec.emplace_back( nullptr );
        for ( size_t i = vec.size() - 1 ; 0 < i ; --i ) {
                vec[ i ] = move( vec[ i - 1 ] );
        }
        vec[ 0 ] = element;
}

const CaseStmt * MultiLevelExitCore::previsit( const CaseStmt * stmt ) {
        visit_children = false;

        // If default, mark seen.
        if ( stmt->isDefault() ) {
                assert( !enclosing_control_structures.empty() );
                enclosing_control_structures.back().seenDefault();
        }

        // The cond may not exist, but if it does update it now.
        visitor->maybe_accept( stmt, &CaseStmt::cond );

        // Just save the mutated node for simplicity.
        CaseStmt * mutStmt = mutate( stmt );

        Label fallLabel = newLabel( "fallThrough", stmt );
        if ( ! mutStmt->stmts.empty() ) {
                // Ensure that the stack isn't corrupted by exceptions in fixBlock.
                auto guard = makeFuncGuard(
                        [&](){ enclosing_control_structures.emplace_back( mutStmt, fallLabel ); },
                        [this](){ enclosing_control_structures.pop_back(); }
                        );

                // These should already be in a block.
                auto block = mutate( mutStmt->stmts.front().strict_as<CompoundStmt>() );
                block->kids = fixBlock( block->kids, true );

                // Add fallthrough label if necessary.
                assert( ! enclosing_control_structures.empty() );
                Entry & entry = enclosing_control_structures.back();
                if ( entry.isFallUsed() ) {
                        mutStmt->stmts.push_back(
                                labelledNullStmt( mutStmt->location, entry.useFallExit() ) );
                }
        }
        assert( ! enclosing_control_structures.empty() );
        Entry & entry = enclosing_control_structures.back();
        assertf( dynamic_cast< const SwitchStmt * >( entry.stmt ),
                         "Control structure enclosing a case clause must be a switch, but is: %s",
                         toString( entry.stmt ).c_str() );
        if ( mutStmt->isDefault() ) {
                if ( entry.isFallDefaultUsed() ) {
                        // Add fallthrough default label if necessary.
                        push_front( mutStmt->stmts, labelledNullStmt(
                                                        stmt->location, entry.useFallDefaultExit()
                                                        ) );
                }
        }
        return mutStmt;
}

void MultiLevelExitCore::previsit( const IfStmt * stmt ) {
        bool labeledBlock = !stmt->labels.empty();
        if ( labeledBlock ) {
                Label breakLabel = newLabel( "blockBreak", stmt );
                enclosing_control_structures.emplace_back( stmt, breakLabel );
                GuardAction( [this](){ enclosing_control_structures.pop_back(); } );
        }
}

const IfStmt * MultiLevelExitCore::postvisit( const IfStmt * stmt ) {
        bool labeledBlock = !stmt->labels.empty();
        if ( labeledBlock ) {
                auto this_label = enclosing_control_structures.back().useBreakExit();
                if ( !this_label.empty() ) {
                        break_label = this_label;
                }
        }
        return stmt;
}

bool isDefaultCase( const ptr<Stmt> & stmt ) {
        const CaseStmt * caseStmt = stmt.strict_as<CaseStmt>();
        return caseStmt->isDefault();
}

void MultiLevelExitCore::previsit( const SwitchStmt * stmt ) {
        Label label = newLabel( "switchBreak", stmt );
        auto it = find_if( stmt->stmts.rbegin(), stmt->stmts.rend(), isDefaultCase );

        const CaseStmt * defaultCase = it != stmt->stmts.rend()
                ? (it)->strict_as<CaseStmt>() : nullptr;
        Label defaultLabel = defaultCase
                ? newLabel( "fallThroughDefault", defaultCase )
                : Label( stmt->location, "" );
        enclosing_control_structures.emplace_back( stmt, label, defaultLabel );
        GuardAction( [this]() { enclosing_control_structures.pop_back(); } );

        // Collect valid labels for fallthrough. It starts with all labels at
        // this level, then remove as each is seen during traversal.
        for ( const Stmt * stmt : stmt->stmts ) {
                auto * caseStmt = strict_dynamic_cast< const CaseStmt * >( stmt );
                if ( caseStmt->stmts.empty() ) continue;
                auto block = caseStmt->stmts.front().strict_as<CompoundStmt>();
                for ( const Stmt * stmt : block->kids ) {
                        for ( const Label & l : stmt->labels ) {
                                fallthrough_labels.insert( l );
                        }
                }
        }
}

const SwitchStmt * MultiLevelExitCore::postvisit( const SwitchStmt * stmt ) {
        assert( !enclosing_control_structures.empty() );
        Entry & entry = enclosing_control_structures.back();
        assert( entry.stmt == stmt );

        // Only run to generate the break label.
        if ( entry.isBreakUsed() ) {
                // To keep the switch statements uniform (all direct children of a
                // SwitchStmt should be CastStmts), append the exit label and break
                // to the last case, create a default case is there are no cases.
                SwitchStmt * mutStmt = mutate( stmt );
                if ( mutStmt->stmts.empty() ) {
                        mutStmt->stmts.push_back( new CaseStmt(
                                                                                  mutStmt->location, nullptr, {} ));
                }

                auto caseStmt = mutStmt->stmts.back().strict_as<CaseStmt>();
                auto mutCase = mutate( caseStmt );
                mutStmt->stmts.back() = mutCase;

                Label label( mutCase->location, "breakLabel" );
                auto branch = new BranchStmt( mutCase->location, BranchStmt::Break, label );
                branch->labels.push_back( entry.useBreakExit() );
                mutCase->stmts.push_back( branch );

                return mutStmt;
        }
        return stmt;
}

void MultiLevelExitCore::previsit( const ReturnStmt * stmt ) {
        if ( inFinally ) {
                SemanticError( stmt->location, "'return' may not appear in a finally clause" );
        }
}

void MultiLevelExitCore::previsit( const TryStmt * stmt ) {
        bool isLabeled = !stmt->labels.empty();
        if ( isLabeled ) {
                Label breakLabel = newLabel( "blockBreak", stmt );
                enclosing_control_structures.emplace_back( stmt, breakLabel );
                GuardAction([this](){ enclosing_control_structures.pop_back(); } );
        }
}

void MultiLevelExitCore::postvisit( const TryStmt * stmt ) {
        bool isLabeled = !stmt->labels.empty();
        if ( isLabeled ) {
                auto this_label = enclosing_control_structures.back().useBreakExit();
                if ( !this_label.empty() ) {
                        break_label = this_label;
                }
        }
}

void MultiLevelExitCore::previsit( const FinallyStmt * ) {
        GuardAction([this, old = move(enclosing_control_structures)](){
                                        enclosing_control_structures = move(old);
                                });
        enclosing_control_structures = vector<Entry>();
        GuardValue( inFinally ) = true;
}

const Stmt * MultiLevelExitCore::mutateLoop(
        const Stmt * body, Entry & entry ) {
        if ( entry.isBreakUsed() ) {
                break_label = entry.useBreakExit();
        }

        if ( entry.isContUsed() ) {
                CompoundStmt * new_body = new CompoundStmt( body->location );
                new_body->kids.push_back( body );
                new_body->kids.push_back(
                        labelledNullStmt( body->location, entry.useContExit() ) );
                return new_body;
        }

        return body;
}

template<typename LoopNode>
void MultiLevelExitCore::prehandleLoopStmt( const LoopNode * loopStmt ) {
        // Remember is loop before going onto mutate the body.
        // The labels will be folded in if they are used.
        Label breakLabel = newLabel( "loopBreak", loopStmt );
        Label contLabel = newLabel( "loopContinue", loopStmt );
        enclosing_control_structures.emplace_back( loopStmt, breakLabel, contLabel );
        GuardAction( [this](){ enclosing_control_structures.pop_back(); } );
}

template<typename LoopNode>
const LoopNode * MultiLevelExitCore::posthandleLoopStmt( const LoopNode * loopStmt ) {
        assert( !enclosing_control_structures.empty() );
        Entry & entry = enclosing_control_structures.back();
        assert( entry.stmt == loopStmt );

        // Now check if the labels are used and add them if so.
        return mutate_field(
                loopStmt, &LoopNode::body, mutateLoop( loopStmt->body, entry ) );
}

list<ptr<Stmt>> MultiLevelExitCore::fixBlock(
        const list<ptr<Stmt>> & kids, bool is_case_clause ) {
        // Unfortunately cannot use automatic error collection.
        SemanticErrorException errors;

        list<ptr<Stmt>> ret;

        // Manually visit each child.
        for ( const ptr<Stmt> & kid : kids ) {
                if ( is_case_clause ) {
                        // Once a label is seen, it's no longer a valid for fallthrough.
                        for ( const Label & l : kid->labels ) {
                                fallthrough_labels.erase( l );
                        }
                }

                try {
                        ret.push_back( kid->accept( *visitor ) );
                } catch ( SemanticErrorException & e ) {
                        errors.append( e );
                }

                if ( !break_label.empty() ) {
                        ret.push_back(
                                labelledNullStmt( ret.back()->location, break_label ) );
                        break_label = Label( CodeLocation(), "" );
                }
        }

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

const CompoundStmt * multiLevelExitUpdate(
        const CompoundStmt * stmt,
        const LabelToStmt & labelTable ) {
        // Must start in the body, so FunctionDecls can be a stopping point.
        Pass<MultiLevelExitCore> visitor( labelTable );
        const CompoundStmt * ret = stmt->accept( visitor );
        return ret;
}
} // namespace ControlStruct

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