src/third_party/mozjs-45/js/src/devtools/rootAnalysis/computeGCTypes.js

/* -*- indent-tabs-mode: nil; js-indent-level: 4 -*- */

"use strict";

loadRelativeToScript('utility.js');
loadRelativeToScript('annotations.js');

var annotatedGCPointers = [];

function processCSU(csu, body)
{
    if (!("DataField" in body))
        return;
    for (var field of body.DataField) {
        var type = field.Field.Type;
        var fieldName = field.Field.Name[0];
        if (type.Kind == "Pointer") {
            var target = type.Type;
            if (target.Kind == "CSU")
                addNestedPointer(csu, target.Name, fieldName);
        }
        if (type.Kind == "Array") {
            var target = type.Type;
            if (target.Kind == "CSU")
                addNestedStructure(csu, target.Name, fieldName);
        }
        if (type.Kind == "CSU") {
            // Ignore nesting in classes which are AutoGCRooters. We only consider
            // types with fields that may not be properly rooted.
            if (type.Name == "JS::AutoGCRooter" || type.Name == "JS::CustomAutoRooter")
                return;
            addNestedStructure(csu, type.Name, fieldName);
        }
    }
    if (isGCPointer(csu))
        annotatedGCPointers.push(csu);
}

var structureParents = {}; // Map from field => list of <parent, fieldName>
var pointerParents = {}; // Map from field => list of <parent, fieldName>

function addNestedStructure(csu, inner, field)
{
    if (!(inner in structureParents))
        structureParents[inner] = [];
    structureParents[inner].push([ csu, field ]);
}

function addNestedPointer(csu, inner, field)
{
    if (!(inner in pointerParents))
        pointerParents[inner] = [];
    pointerParents[inner].push([ csu, field ]);
}

var xdb = xdbLibrary();
xdb.open("src_comp.xdb");

var minStream = xdb.min_data_stream();
var maxStream = xdb.max_data_stream();

for (var csuIndex = minStream; csuIndex <= maxStream; csuIndex++) {
    var csu = xdb.read_key(csuIndex);
    var data = xdb.read_entry(csu);
    var json = JSON.parse(data.readString());
    assert(json.length == 1);
    processCSU(csu.readString(), json[0]);

    xdb.free_string(csu);
    xdb.free_string(data);
}

var gcTypes = {}; // map from parent struct => Set of GC typed children
var gcPointers = {}; // map from parent struct => Set of GC typed children
var nonGCTypes = {}; // set of types that would ordinarily be GC types but we are suppressing
var nonGCPointers = {}; // set of types that would ordinarily be GC pointers but we are suppressing
var gcFields = new Map;

function stars(n) { return n ? '*' + stars(n-1) : '' };

// "typeName is a (pointer to a)^'typePtrLevel' GC type because it contains a field
// named 'child' of type 'why' (or pointer to 'why' if fieldPtrLevel == 1), which is
// itself a GCThing or GCPointer."
function markGCType(typeName, child, why, typePtrLevel, fieldPtrLevel, indent)
{
    //printErr(`${indent}${typeName}${stars(typePtrLevel)} may be a gctype/ptr because of its child '${child}' of type ${why}${stars(fieldPtrLevel)}`);

    // Some types, like UniquePtr, do not mark/trace/relocate their contained
    // pointers and so should not hold them live across a GC. UniquePtr in
    // particular should be the only thing pointing to a structure containing a
    // GCPointer, so nothing else can possibly trace it and it'll die when the
    // UniquePtr goes out of scope. So we say that memory pointed to by a
    // UniquePtr is just as unsafe as the stack for storing GC pointers.
    if (!fieldPtrLevel && isUnsafeStorage(typeName)) {
        // The UniquePtr itself is on the stack but when you dereference the
        // contained pointer, you get to the unsafe memory that we are treating
        // as if it were the stack (aka ptrLevel 0). Note that
        // UniquePtr<UniquePtr<JSObject*>> is fine, so we don't want to just
        // hardcode the ptrLevel.
        fieldPtrLevel = -1;
    }

    // Example: with:
    //    struct Pair { JSObject* foo; int bar; };
    //    struct { Pair** info }***
    // make a call to:
    //    child='info' typePtrLevel=3 fieldPtrLevel=2
    // for a final ptrLevel of 5, used to later call:
    //    child='foo' typePtrLevel=5 fieldPtrLevel=1
    //
    var ptrLevel = typePtrLevel + fieldPtrLevel;

    // ...except when > 2 levels of pointers away from an actual GC thing, stop
    // searching the graph. (This would just be > 1, except that a UniquePtr
    // field might still have a GC pointer.)
    if (ptrLevel > 2)
        return;

    if (ptrLevel == 0 && isRootedGCTypeName(typeName))
        return;
    if (ptrLevel == 1 && isRootedGCPointerTypeName(typeName))
        return;

    if (ptrLevel == 0) {
        if (typeName in nonGCTypes)
            return;
        if (!(typeName in gcTypes))
            gcTypes[typeName] = new Set();
        gcTypes[typeName].add(why);
    } else if (ptrLevel == 1) {
        if (typeName in nonGCPointers)
            return;
        if (!(typeName in gcPointers))
            gcPointers[typeName] = new Set();
        gcPointers[typeName].add(why);
    }

    if (ptrLevel < 2) {
        if (!gcFields.has(typeName))
            gcFields.set(typeName, new Map());
        gcFields.get(typeName).set(child, [ why, fieldPtrLevel ]);
    }

    if (typeName in structureParents) {
        for (var field of structureParents[typeName]) {
            var [ holderType, fieldName ] = field;
            markGCType(holderType, fieldName, typeName, ptrLevel, 0, indent + "  ");
        }
    }
    if (typeName in pointerParents) {
        for (var field of pointerParents[typeName]) {
            var [ holderType, fieldName ] = field;
            markGCType(holderType, fieldName, typeName, ptrLevel, 1, indent + "  ");
        }
    }
}

function addGCType(typeName, child, why, depth, fieldPtrLevel)
{
    markGCType(typeName, '<annotation>', '(annotation)', 0, 0, "");
}

function addGCPointer(typeName)
{
    markGCType(typeName, '<pointer-annotation>', '(annotation)', 1, 0, "");
}

for (var type of listNonGCTypes())
    nonGCTypes[type] = true;
for (var type of listNonGCPointers())
    nonGCPointers[type] = true;
for (var type of listGCTypes())
    addGCType(type);
for (var type of listGCPointers())
    addGCPointer(type);

for (var typeName of annotatedGCPointers)
    addGCPointer(typeName);

function explain(csu, indent, seen) {
    if (!seen)
        seen = new Set();
    seen.add(csu);
    if (!gcFields.has(csu))
        return;
    var fields = gcFields.get(csu);

    if (fields.has('<annotation>')) {
        print(indent + "which is a GCThing because I said so");
        return;
    }
    if (fields.has('<pointer-annotation>')) {
        print(indent + "which is a GCPointer because I said so");
        return;
    }
    for (var [ field, [ child, ptrdness ] ] of fields) {
        var inherit = "";
        if (field == "field:0")
            inherit = " (probably via inheritance)";
        var msg = indent + "contains field '" + field + "' ";
        if (ptrdness == -1)
            msg += "(with a pointer to unsafe storage) holding a ";
        else if (ptrdness == 0)
            msg += "of type ";
        else
            msg += "pointing to type ";
        msg += child + inherit;
        print(msg);
        if (!seen.has(child))
            explain(child, indent + "  ", seen);
    }
}

for (var csu in gcTypes) {
    print("GCThing: " + csu);
    explain(csu, "  ");
}
for (var csu in gcPointers) {
    print("GCPointer: " + csu);
    explain(csu, "  ");
}