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NodeStack

PushResult

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Line Code
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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "frontend/ParseNode-inl.h"

#include "frontend/Parser.h"

#include "jscntxtinlines.h"

using namespace js;
using namespace js::frontend;

using mozilla::ArrayLength;
using mozilla::IsFinite;

#ifdef DEBUG
void
ParseNode::checkListConsistency()
{
    MOZ_ASSERT(isArity(PN_LIST));
    ParseNode** tail;
    uint32_t count = 0;
    if (pn_head) {
        ParseNode* last = pn_head;
        ParseNode* pn = last;
        while (pn) {
            last = pn;
            pn = pn->pn_next;
            count++;
        }

        tail = &last->pn_next;
    } else {
        tail = &pn_head;
    }
    MOZ_ASSERT(pn_tail == tail);
    MOZ_ASSERT(pn_count == count);
}
#endif

/* Add |node| to |parser|'s free node list. */
void
ParseNodeAllocator::freeNode(ParseNode* pn)
{
    /* Catch back-to-back dup recycles. */
    MOZ_ASSERT(pn != freelist);

#ifdef DEBUG
    /* Poison the node, to catch attempts to use it without initializing it. */
    memset(pn, 0xab, sizeof(*pn));
#endif

    pn->pn_next = freelist;
    freelist = pn;
}

namespace {

/*
 * A work pool of ParseNodes. The work pool is a stack, chained together
 * by nodes' pn_next fields. We use this to avoid creating deep C++ stacks
 * when recycling deep parse trees.
 *
 * Since parse nodes are probably allocated in something close to the order
 * they appear in a depth-first traversal of the tree, making the work pool
 * a stack should give us pretty good locality.
 */
class NodeStack {
  public:
    NodeStack() : top(nullptr) { }
    bool empty() { return top == nullptr; }
    void push(ParseNode* pn) {
        pn->pn_next = top;
        top = pn;
    }
    /* Push the children of the PN_LIST node |pn| on the stack. */
    void pushList(ParseNode* pn) {
        /* This clobbers pn->pn_head if the list is empty; should be okay. */
        *pn->pn_tail = top;
        top = pn->pn_head;
    }
    ParseNode* pop() {
        MOZ_ASSERT(!empty());
        ParseNode* hold = top; /* my kingdom for a prog1 */
        top = top->pn_next;
        return hold;
    }
  private:
    ParseNode* top;
};

} /* anonymous namespace */

enum class PushResult { Recyclable, CleanUpLater };

static PushResult
PushCodeNodeChildren(ParseNode* node, NodeStack* stack)
{
    MOZ_ASSERT(node->isArity(PN_CODE));

    /*
     * Function nodes are linked into the function box tree, and may appear
     * on method lists. Both of those lists are singly-linked, so trying to
     * update them now could result in quadratic behavior when recycling
     * trees containing many functions; and the lists can be very long. So
     * we put off cleaning the lists up until just before function
     * analysis, when we call CleanFunctionList.
     *
     * In fact, we can't recycle the parse node yet, either: it may appear
     * on a method list, and reusing the node would corrupt that. Instead,
     * we clear its pn_funbox pointer to mark it as deleted;
     * CleanFunctionList recycles it as well.
     *
     * We do recycle the nodes around it, though, so we must clear pointers
     * to them to avoid leaving dangling references where someone can find
     * them.
     */
    node->pn_funbox = nullptr;
    if (node->pn_body)
        stack->push(node->pn_body);
    node->pn_body = nullptr;

    return PushResult::CleanUpLater;
}

static PushResult
PushNameNodeChildren(ParseNode* node, NodeStack* stack)
{
    MOZ_ASSERT(node->isArity(PN_NAME));

    if (node->pn_expr)
        stack->push(node->pn_expr);
    node->pn_expr = nullptr;
    return PushResult::Recyclable;
}

static PushResult
PushScopeNodeChildren(ParseNode* node, NodeStack* stack)
{
    MOZ_ASSERT(node->isArity(PN_SCOPE));

    if (node->scopeBody())
        stack->push(node->scopeBody());
    node->setScopeBody(nullptr);
    return PushResult::Recyclable;
}

static PushResult
PushListNodeChildren(ParseNode* node, NodeStack* stack)
{
    MOZ_ASSERT(node->isArity(PN_LIST));
    node->checkListConsistency();

    stack->pushList(node);

    return PushResult::Recyclable;
}

static PushResult
PushUnaryNodeChild(ParseNode* node, NodeStack* stack)
{
    MOZ_ASSERT(node->isArity(PN_UNARY));

    stack->push(node->pn_kid);

    return PushResult::Recyclable;
}

/*
 * Push the children of |pn| on |stack|. Return true if |pn| itself could be
 * safely recycled, or false if it must be cleaned later (pn_used and pn_defn
 * nodes, and all function nodes; see comments for CleanFunctionList in
 * SemanticAnalysis.cpp). Some callers want to free |pn|; others
 * (js::ParseNodeAllocator::prepareNodeForMutation) don't care about |pn|, and
 * just need to take care of its children.
 */
static PushResult
PushNodeChildren(ParseNode* pn, NodeStack* stack)
{
    switch (pn->getKind()) {
      // Trivial nodes that refer to no nodes, are referred to by nothing
      // but their parents, are never used, and are never a definition.
      case PNK_NOP:
      case PNK_STRING:
      case PNK_TEMPLATE_STRING:
      case PNK_REGEXP:
      case PNK_TRUE:
      case PNK_FALSE:
      case PNK_NULL:
      case PNK_RAW_UNDEFINED:
      case PNK_ELISION:
      case PNK_GENERATOR:
      case PNK_NUMBER:
      case PNK_BREAK:
      case PNK_CONTINUE:
      case PNK_DEBUGGER:
      case PNK_EXPORT_BATCH_SPEC:
      case PNK_OBJECT_PROPERTY_NAME:
      case PNK_POSHOLDER:
        MOZ_ASSERT(pn->isArity(PN_NULLARY));
        return PushResult::Recyclable;

      // Nodes with a single non-null child.
      case PNK_TYPEOFNAME:
      case PNK_TYPEOFEXPR:
      case PNK_VOID:
      case PNK_NOT:
      case PNK_BITNOT:
      case PNK_THROW:
      case PNK_DELETENAME:
      case PNK_DELETEPROP:
      case PNK_DELETEELEM:
      case PNK_DELETEEXPR:
      case PNK_POS:
      case PNK_NEG:
      case PNK_PREINCREMENT:
      case PNK_POSTINCREMENT:
      case PNK_PREDECREMENT:
      case PNK_POSTDECREMENT:
      case PNK_COMPUTED_NAME:
      case PNK_ARRAYPUSH:
      case PNK_SPREAD:
      case PNK_MUTATEPROTO:
      case PNK_EXPORT:
      case PNK_SUPERBASE:
        return PushUnaryNodeChild(pn, stack);

      // Nodes with a single nullable child.
      case PNK_THIS:
      case PNK_SEMI: {
        MOZ_ASSERT(pn->isArity(PN_UNARY));
        if (pn->pn_kid)
            stack->push(pn->pn_kid);
        return PushResult::Recyclable;
      }

      // Binary nodes with two non-null children.

      // All assignment and compound assignment nodes qualify.
      case PNK_ASSIGN:
      case PNK_ADDASSIGN:
      case PNK_SUBASSIGN:
      case PNK_BITORASSIGN:
      case PNK_BITXORASSIGN:
      case PNK_BITANDASSIGN:
      case PNK_LSHASSIGN:
      case PNK_RSHASSIGN:
      case PNK_URSHASSIGN:
      case PNK_MULASSIGN:
      case PNK_DIVASSIGN:
      case PNK_MODASSIGN:
      case PNK_POWASSIGN:
      // ...and a few others.
      case PNK_ELEM:
      case PNK_IMPORT_SPEC:
      case PNK_EXPORT_SPEC:
      case PNK_COLON:
      case PNK_SHORTHAND:
      case PNK_DOWHILE:
      case PNK_WHILE:
      case PNK_SWITCH:
      case PNK_CLASSMETHOD:
      case PNK_NEWTARGET:
      case PNK_SETTHIS:
      case PNK_FOR:
      case PNK_COMPREHENSIONFOR:
      case PNK_WITH: {
        MOZ_ASSERT(pn->isArity(PN_BINARY));
        stack->push(pn->pn_left);
        stack->push(pn->pn_right);
        return PushResult::Recyclable;
      }

      // Default clauses are PNK_CASE but do not have case expressions.
      // Named class expressions do not have outer binding nodes.
      // So both are binary nodes with a possibly-null pn_left.
      case PNK_CASE:
      case PNK_CLASSNAMES: {
        MOZ_ASSERT(pn->isArity(PN_BINARY));
        if (pn->pn_left)
            stack->push(pn->pn_left);
        stack->push(pn->pn_right);
        return PushResult::Recyclable;
      }

      // The child is an assignment of a PNK_GENERATOR node to the
      // '.generator' local, for a synthesized, prepended initial yield.
      case PNK_INITIALYIELD: {
        MOZ_ASSERT(pn->isArity(PN_UNARY));
        MOZ_ASSERT(pn->pn_kid->isKind(PNK_ASSIGN) &&
                   pn->pn_kid->pn_left->isKind(PNK_NAME) &&
                   pn->pn_kid->pn_right->isKind(PNK_GENERATOR));
        stack->push(pn->pn_kid);
        return PushResult::Recyclable;
      }

      // The child is the expression being yielded.
      case PNK_YIELD_STAR:
      case PNK_YIELD:
      case PNK_AWAIT: {
        MOZ_ASSERT(pn->isArity(PN_UNARY));
        if (pn->pn_kid)
            stack->push(pn->pn_kid);
        return PushResult::Recyclable;
      }

      // A return node's child is what you'd expect: the return expression,
      // if any.
      case PNK_RETURN: {
        MOZ_ASSERT(pn->isArity(PN_UNARY));
        if (pn->pn_kid)
            stack->push(pn->pn_kid);
        return PushResult::Recyclable;
      }

      // Import and export-from nodes have a list of specifiers on the left
      // and a module string on the right.
      case PNK_IMPORT:
      case PNK_EXPORT_FROM: {
        MOZ_ASSERT(pn->isArity(PN_BINARY));
        MOZ_ASSERT_IF(pn->isKind(PNK_IMPORT), pn->pn_left->isKind(PNK_IMPORT_SPEC_LIST));
        MOZ_ASSERT_IF(pn->isKind(PNK_EXPORT_FROM), pn->pn_left->isKind(PNK_EXPORT_SPEC_LIST));
        MOZ_ASSERT(pn->pn_left->isArity(PN_LIST));
        MOZ_ASSERT(pn->pn_right->isKind(PNK_STRING));
        stack->pushList(pn->pn_left);
        stack->push(pn->pn_right);
        return PushResult::Recyclable;
      }

      case PNK_EXPORT_DEFAULT: {
        MOZ_ASSERT(pn->isArity(PN_BINARY));
        MOZ_ASSERT_IF(pn->pn_right, pn->pn_right->isKind(PNK_NAME));
        stack->push(pn->pn_left);
        if (pn->pn_right)
            stack->push(pn->pn_right);
        return PushResult::Recyclable;
      }

      // Ternary nodes with all children non-null.
      case PNK_CONDITIONAL: {
        MOZ_ASSERT(pn->isArity(PN_TERNARY));
        stack->push(pn->pn_kid1);
        stack->push(pn->pn_kid2);
        stack->push(pn->pn_kid3);
        return PushResult::Recyclable;
      }

      // For for-in and for-of, the first child is the left-hand side of the
      // 'in' or 'of' (a declaration or an assignment target). The second
      // child is always null, and the third child is the expression looped
      // over.  For example, in |for (var p in obj)|, the first child is |var
      // p|, the second child is null, and the third child is |obj|.
      case PNK_FORIN:
      case PNK_FOROF: {
        MOZ_ASSERT(pn->isArity(PN_TERNARY));
        MOZ_ASSERT(!pn->pn_kid2);
        stack->push(pn->pn_kid1);
        stack->push(pn->pn_kid3);
        return PushResult::Recyclable;
      }

      // for (;;) nodes have one child per optional component of the loop head.
      case PNK_FORHEAD: {
        MOZ_ASSERT(pn->isArity(PN_TERNARY));
        if (pn->pn_kid1)
            stack->push(pn->pn_kid1);
        if (pn->pn_kid2)
            stack->push(pn->pn_kid2);
        if (pn->pn_kid3)
            stack->push(pn->pn_kid3);
        return PushResult::Recyclable;
      }

      // classes might have an optional node for the heritage, as well as the names
      case PNK_CLASS: {
        MOZ_ASSERT(pn->isArity(PN_TERNARY));
        if (pn->pn_kid1)
            stack->push(pn->pn_kid1);
        if (pn->pn_kid2)
            stack->push(pn->pn_kid2);
        stack->push(pn->pn_kid3);
        return PushResult::Recyclable;
      }

      // if-statement nodes have condition and consequent children and a
      // possibly-null alternative.
      case PNK_IF: {
        MOZ_ASSERT(pn->isArity(PN_TERNARY));
        stack->push(pn->pn_kid1);
        stack->push(pn->pn_kid2);
        if (pn->pn_kid3)
            stack->push(pn->pn_kid3);
        return PushResult::Recyclable;
      }

      // try-statements have statements to execute, and one or both of a
      // catch-list and a finally-block.
      case PNK_TRY: {
        MOZ_ASSERT(pn->isArity(PN_TERNARY));
        MOZ_ASSERT(pn->pn_kid2 || pn->pn_kid3);
        stack->push(pn->pn_kid1);
        if (pn->pn_kid2)
            stack->push(pn->pn_kid2);
        if (pn->pn_kid3)
            stack->push(pn->pn_kid3);
        return PushResult::Recyclable;
      }

      // A catch node has first kid as catch-variable pattern, the second kid
      // as catch condition (which, if non-null, records the |<cond>| in
      // SpiderMonkey's |catch (e if <cond>)| extension), and third kid as the
      // statements in the catch block.
      case PNK_CATCH: {
        MOZ_ASSERT(pn->isArity(PN_TERNARY));
        stack->push(pn->pn_kid1);
        if (pn->pn_kid2)
            stack->push(pn->pn_kid2);
        stack->push(pn->pn_kid3);
        return PushResult::Recyclable;
      }

      // List nodes with all non-null children.
      case PNK_OR:
      case PNK_AND:
      case PNK_BITOR:
      case PNK_BITXOR:
      case PNK_BITAND:
      case PNK_STRICTEQ:
      case PNK_EQ:
      case PNK_STRICTNE:
      case PNK_NE:
      case PNK_LT:
      case PNK_LE:
      case PNK_GT:
      case PNK_GE:
      case PNK_INSTANCEOF:
      case PNK_IN:
      case PNK_LSH:
      case PNK_RSH:
      case PNK_URSH:
      case PNK_ADD:
      case PNK_SUB:
      case PNK_STAR:
      case PNK_DIV:
      case PNK_MOD:
      case PNK_POW:
      case PNK_COMMA:
      case PNK_NEW:
      case PNK_CALL:
      case PNK_SUPERCALL:
      case PNK_GENEXP:
      case PNK_ARRAY:
      case PNK_OBJECT:
      case PNK_TEMPLATE_STRING_LIST:
      case PNK_TAGGED_TEMPLATE:
      case PNK_CALLSITEOBJ:
      case PNK_VAR:
      case PNK_CONST:
      case PNK_LET:
      case PNK_CATCHLIST:
      case PNK_STATEMENTLIST:
      case PNK_IMPORT_SPEC_LIST:
      case PNK_EXPORT_SPEC_LIST:
      case PNK_PARAMSBODY:
      case PNK_CLASSMETHODLIST:
        return PushListNodeChildren(pn, stack);

      // Array comprehension nodes are lists with a single child:
      // PNK_COMPREHENSIONFOR for comprehensions, PNK_LEXICALSCOPE for legacy
      // comprehensions.  Probably this should be a non-list eventually.
      case PNK_ARRAYCOMP: {
#ifdef DEBUG
        MOZ_ASSERT(pn->isKind(PNK_ARRAYCOMP));
        MOZ_ASSERT(pn->isArity(PN_LIST));
        MOZ_ASSERT(pn->pn_count == 1);
        MOZ_ASSERT(pn->pn_head->isKind(PNK_LEXICALSCOPE) ||
                   pn->pn_head->isKind(PNK_COMPREHENSIONFOR));
#endif
        return PushListNodeChildren(pn, stack);
      }

      case PNK_LABEL:
      case PNK_DOT:
      case PNK_NAME:
        return PushNameNodeChildren(pn, stack);

      case PNK_LEXICALSCOPE:
        return PushScopeNodeChildren(pn, stack);

      case PNK_FUNCTION:
      case PNK_MODULE:
        return PushCodeNodeChildren(pn, stack);

      case PNK_LIMIT: // invalid sentinel value
        MOZ_CRASH("invalid node kind");
    }

    MOZ_CRASH("bad ParseNodeKind");
    return PushResult::CleanUpLater;
}

/*
 * Prepare |pn| to be mutated in place into a new kind of node. Recycle all
 * |pn|'s recyclable children (but not |pn| itself!), and disconnect it from
 * metadata structures (the function box tree).
 */
void
ParseNodeAllocator::prepareNodeForMutation(ParseNode* pn)
{
    // Nothing to do for nullary nodes.
    if (pn->isArity(PN_NULLARY))
        return;

    // Put |pn|'s children (but not |pn| itself) on a work stack.
    NodeStack stack;
    PushNodeChildren(pn, &stack);

    // For each node on the work stack, push its children on the work stack,
    // and free the node if we can.
    while (!stack.empty()) {
        pn = stack.pop();
        if (PushNodeChildren(pn, &stack) == PushResult::Recyclable)
            freeNode(pn);
    }
}

/*
 * Return the nodes in the subtree |pn| to the parser's free node list, for
 * reallocation.
 */
ParseNode*
ParseNodeAllocator::freeTree(ParseNode* pn)
{
    if (!pn)
        return nullptr;

    ParseNode* savedNext = pn->pn_next;

    NodeStack stack;
    for (;;) {
        if (PushNodeChildren(pn, &stack) == PushResult::Recyclable)
            freeNode(pn);
        if (stack.empty())
            break;
        pn = stack.pop();
    }

    return savedNext;
}

/*
 * Allocate a ParseNode from parser's node freelist or, failing that, from
 * cx's temporary arena.
 */
void*
ParseNodeAllocator::allocNode()
{
    if (ParseNode* pn = freelist) {
        freelist = pn->pn_next;
        return pn;
    }

    LifoAlloc::AutoFallibleScope fallibleAllocator(&alloc);
    void* p = alloc.alloc(sizeof (ParseNode));
    if (!p)
        ReportOutOfMemory(cx);
    return p;
}

ParseNode*
ParseNode::appendOrCreateList(ParseNodeKind kind, JSOp op, ParseNode* left, ParseNode* right,
                              FullParseHandler* handler, ParseContext* pc)
{
    // The asm.js specification is written in ECMAScript grammar terms that
    // specify *only* a binary tree.  It's a royal pain to implement the asm.js
    // spec to act upon n-ary lists as created below.  So for asm.js, form a
    // binary tree of lists exactly as ECMAScript would by skipping the
    // following optimization.
    if (!pc->useAsmOrInsideUseAsm()) {
        // Left-associative trees of a given operator (e.g. |a + b + c|) are
        // binary trees in the spec: (+ (+ a b) c) in Lisp terms.  Recursively
        // processing such a tree, exactly implemented that way, would blow the
        // the stack.  We use a list node that uses O(1) stack to represent
        // such operations: (+ a b c).
        //
        // (**) is right-associative; per spec |a ** b ** c| parses as
        // (** a (** b c)). But we treat this the same way, creating a list
        // node: (** a b c). All consumers must understand that this must be
        // processed with a right fold, whereas the list (+ a b c) must be
        // processed with a left fold because (+) is left-associative.
        //
        if (left->isKind(kind) &&
            left->isOp(op) &&
            (CodeSpec[op].format & JOF_LEFTASSOC ||
             (kind == PNK_POW && !left->pn_parens)))
        {
            ListNode* list = &left->as<ListNode>();

            list->append(right);
            list->pn_pos.end = right->pn_pos.end;

            return list;
        }
    }

    ParseNode* list = handler->new_<ListNode>(kind, op, left);
    if (!list)
        return nullptr;