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BytecodeEmitter.cpp
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BytecodeEmitter.cpp
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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/. */
/*
* JS bytecode generation.
*/
#include "frontend/BytecodeEmitter.h"
#include "mozilla/ArrayUtils.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/FloatingPoint.h"
#include "mozilla/Maybe.h"
#include "mozilla/PodOperations.h"
#include "mozilla/UniquePtr.h"
#include <string.h>
#include "jsapi.h"
#include "jsatom.h"
#include "jscntxt.h"
#include "jsfun.h"
#include "jsnum.h"
#include "jsopcode.h"
#include "jsscript.h"
#include "jstypes.h"
#include "jsutil.h"
#include "asmjs/AsmJSLink.h"
#include "frontend/Parser.h"
#include "frontend/TokenStream.h"
#include "vm/Debugger.h"
#include "vm/GeneratorObject.h"
#include "vm/Stack.h"
#include "jsatominlines.h"
#include "jsobjinlines.h"
#include "jsscriptinlines.h"
#include "frontend/ParseMaps-inl.h"
#include "frontend/ParseNode-inl.h"
#include "vm/NativeObject-inl.h"
#include "vm/ScopeObject-inl.h"
using namespace js;
using namespace js::gc;
using namespace js::frontend;
using mozilla::Maybe;
using mozilla::Some;
using mozilla::DebugOnly;
using mozilla::NumberIsInt32;
using mozilla::PodCopy;
using mozilla::UniquePtr;
struct frontend::StmtInfoBCE : public StmtInfoBase
{
StmtInfoBCE* enclosing;
StmtInfoBCE* enclosingScope;
ptrdiff_t update; /* loop update offset (top if none) */
ptrdiff_t breaks; /* offset of last break in loop */
ptrdiff_t continues; /* offset of last continue in loop */
uint32_t blockScopeIndex; /* index of scope in BlockScopeArray */
explicit StmtInfoBCE(ExclusiveContext* cx) : StmtInfoBase(cx) {}
void setTop(ptrdiff_t top) {
update = top;
breaks = -1;
continues = -1;
}
/*
* To reuse space, alias two of the ptrdiff_t fields for use during
* try/catch/finally code generation and backpatching.
*
* Only a loop, switch, or label statement info record can have breaks and
* continues, and only a for loop has an update backpatch chain, so it's
* safe to overlay these for the "trying" StmtTypes.
*/
ptrdiff_t& gosubs() {
MOZ_ASSERT(type == StmtType::FINALLY);
return breaks;
}
ptrdiff_t& guardJump() {
MOZ_ASSERT(type == StmtType::TRY || type == StmtType::FINALLY);
return continues;
}
};
struct frontend::LoopStmtInfo : public StmtInfoBCE
{
int32_t stackDepth; // Stack depth when this loop was pushed.
uint32_t loopDepth; // Loop depth.
// Can we OSR into Ion from here? True unless there is non-loop state on the stack.
bool canIonOsr;
explicit LoopStmtInfo(ExclusiveContext* cx) : StmtInfoBCE(cx) {}
static LoopStmtInfo* fromStmtInfo(StmtInfoBCE* stmt) {
MOZ_ASSERT(stmt->isLoop());
return static_cast<LoopStmtInfo*>(stmt);
}
};
BytecodeEmitter::BytecodeEmitter(BytecodeEmitter* parent,
Parser<FullParseHandler>* parser, SharedContext* sc,
HandleScript script, Handle<LazyScript*> lazyScript,
bool insideEval, HandleScript evalCaller,
bool insideNonGlobalEval, uint32_t lineNum,
EmitterMode emitterMode)
: sc(sc),
cx(sc->context),
parent(parent),
script(cx, script),
lazyScript(cx, lazyScript),
prologue(cx, lineNum),
main(cx, lineNum),
current(&main),
parser(parser),
evalCaller(evalCaller),
stmtStack(cx),
atomIndices(cx),
firstLine(lineNum),
localsToFrameSlots_(cx),
stackDepth(0), maxStackDepth(0),
arrayCompDepth(0),
emitLevel(0),
constList(cx),
tryNoteList(cx),
blockScopeList(cx),
yieldOffsetList(cx),
typesetCount(0),
hasSingletons(false),
hasTryFinally(false),
emittingForInit(false),
emittingRunOnceLambda(false),
insideEval(insideEval),
insideNonGlobalEval(insideNonGlobalEval),
insideModule(false),
emitterMode(emitterMode)
{
MOZ_ASSERT_IF(evalCaller, insideEval);
MOZ_ASSERT_IF(emitterMode == LazyFunction, lazyScript);
}
bool
BytecodeEmitter::init()
{
return atomIndices.ensureMap(cx);
}
bool
BytecodeEmitter::updateLocalsToFrameSlots()
{
// Assign stack slots to unaliased locals (aliased locals are stored in the
// call object and don't need their own stack slots). We do this by filling
// a Vector that can be used to map a local to its stack slot.
if (localsToFrameSlots_.length() == script->bindings.numLocals()) {
// CompileScript calls updateNumBlockScoped to update the block scope
// depth. Do nothing if the depth didn't change.
return true;
}
localsToFrameSlots_.clear();
if (!localsToFrameSlots_.reserve(script->bindings.numLocals()))
return false;
uint32_t slot = 0;
for (BindingIter bi(script); !bi.done(); bi++) {
if (bi->kind() == Binding::ARGUMENT)
continue;
if (bi->aliased())
localsToFrameSlots_.infallibleAppend(UINT32_MAX);
else
localsToFrameSlots_.infallibleAppend(slot++);
}
for (size_t i = 0; i < script->bindings.numBlockScoped(); i++)
localsToFrameSlots_.infallibleAppend(slot++);
return true;
}
bool
BytecodeEmitter::emitCheck(ptrdiff_t delta, ptrdiff_t* offset)
{
*offset = code().length();
// Start it off moderately large to avoid repeated resizings early on.
// ~98% of cases fit within 1024 bytes.
if (code().capacity() == 0 && !code().reserve(1024))
return false;
if (!code().growBy(delta)) {
ReportOutOfMemory(cx);
return false;
}
return true;
}
void
BytecodeEmitter::updateDepth(ptrdiff_t target)
{
jsbytecode* pc = code(target);
int nuses = StackUses(nullptr, pc);
int ndefs = StackDefs(nullptr, pc);
stackDepth -= nuses;
MOZ_ASSERT(stackDepth >= 0);
stackDepth += ndefs;
if ((uint32_t)stackDepth > maxStackDepth)
maxStackDepth = stackDepth;
}
#ifdef DEBUG
bool
BytecodeEmitter::checkStrictOrSloppy(JSOp op)
{
if (IsCheckStrictOp(op) && !sc->strict())
return false;
if (IsCheckSloppyOp(op) && sc->strict())
return false;
return true;
}
#endif
bool
BytecodeEmitter::emit1(JSOp op)
{
MOZ_ASSERT(checkStrictOrSloppy(op));
ptrdiff_t offset;
if (!emitCheck(1, &offset))
return false;
jsbytecode* code = this->code(offset);
code[0] = jsbytecode(op);
updateDepth(offset);
return true;
}
bool
BytecodeEmitter::emit2(JSOp op, uint8_t op1)
{
MOZ_ASSERT(checkStrictOrSloppy(op));
ptrdiff_t offset;
if (!emitCheck(2, &offset))
return false;
jsbytecode* code = this->code(offset);
code[0] = jsbytecode(op);
code[1] = jsbytecode(op1);
updateDepth(offset);
return true;
}
bool
BytecodeEmitter::emit3(JSOp op, jsbytecode op1, jsbytecode op2)
{
MOZ_ASSERT(checkStrictOrSloppy(op));
/* These should filter through emitVarOp. */
MOZ_ASSERT(!IsArgOp(op));
MOZ_ASSERT(!IsLocalOp(op));
ptrdiff_t offset;
if (!emitCheck(3, &offset))
return false;
jsbytecode* code = this->code(offset);
code[0] = jsbytecode(op);
code[1] = op1;
code[2] = op2;
updateDepth(offset);
return true;
}
bool
BytecodeEmitter::emitN(JSOp op, size_t extra, ptrdiff_t* offset)
{
MOZ_ASSERT(checkStrictOrSloppy(op));
ptrdiff_t length = 1 + ptrdiff_t(extra);
ptrdiff_t off;
if (!emitCheck(length, &off))
return false;
jsbytecode* code = this->code(off);
code[0] = jsbytecode(op);
/* The remaining |extra| bytes are set by the caller */
/*
* Don't updateDepth if op's use-count comes from the immediate
* operand yet to be stored in the extra bytes after op.
*/
if (CodeSpec[op].nuses >= 0)
updateDepth(off);
if (offset)
*offset = off;
return true;
}
bool
BytecodeEmitter::emitJump(JSOp op, ptrdiff_t off, ptrdiff_t* jumpOffset)
{
ptrdiff_t offset;
if (!emitCheck(5, &offset))
return false;
jsbytecode* code = this->code(offset);
code[0] = jsbytecode(op);
SET_JUMP_OFFSET(code, off);
updateDepth(offset);
if (jumpOffset)
*jumpOffset = offset;
return true;
}
bool
BytecodeEmitter::emitCall(JSOp op, uint16_t argc, ParseNode* pn)
{
if (pn && !updateSourceCoordNotes(pn->pn_pos.begin))
return false;
return emit3(op, ARGC_HI(argc), ARGC_LO(argc));
}
bool
BytecodeEmitter::emitDupAt(unsigned slotFromTop)
{
MOZ_ASSERT(slotFromTop < unsigned(stackDepth));
if (slotFromTop >= JS_BIT(24)) {
reportError(nullptr, JSMSG_TOO_MANY_LOCALS);
return false;
}
ptrdiff_t off;
if (!emitN(JSOP_DUPAT, 3, &off))
return false;
jsbytecode* pc = code(off);
SET_UINT24(pc, slotFromTop);
return true;
}
/* XXX too many "... statement" L10N gaffes below -- fix via js.msg! */
const char js_with_statement_str[] = "with statement";
const char js_finally_block_str[] = "finally block";
static const char * const statementName[] = {
"label statement", /* LABEL */
"if statement", /* IF */
"else statement", /* ELSE */
"destructuring body", /* BODY */
"switch statement", /* SWITCH */
"block", /* BLOCK */
js_with_statement_str, /* WITH */
"catch block", /* CATCH */
"try block", /* TRY */
js_finally_block_str, /* FINALLY */
js_finally_block_str, /* SUBROUTINE */
"do loop", /* DO_LOOP */
"for loop", /* FOR_LOOP */
"for/in loop", /* FOR_IN_LOOP */
"for/of loop", /* FOR_OF_LOOP */
"while loop", /* WHILE_LOOP */
"spread", /* SPREAD */
};
static_assert(MOZ_ARRAY_LENGTH(statementName) == uint16_t(StmtType::LIMIT),
"statementName array and StmtType enum must be consistent");
static const char*
StatementName(StmtInfoBCE* stmt)
{
if (!stmt)
return js_script_str;
return statementName[uint16_t(stmt->type)];
}
static void
ReportStatementTooLarge(TokenStream& ts, StmtInfoBCE* stmt)
{
ts.reportError(JSMSG_NEED_DIET, StatementName(stmt));
}
/*
* Emit a backpatch op with offset pointing to the previous jump of this type,
* so that we can walk back up the chain fixing up the op and jump offset.
*/
bool
BytecodeEmitter::emitBackPatchOp(ptrdiff_t* lastp)
{
ptrdiff_t delta = offset() - *lastp;
*lastp = offset();
MOZ_ASSERT(delta > 0);
return emitJump(JSOP_BACKPATCH, delta);
}
static inline unsigned
LengthOfSetLine(unsigned line)
{
return 1 /* SN_SETLINE */ + (line > SN_4BYTE_OFFSET_MASK ? 4 : 1);
}
/* Updates line number notes, not column notes. */
bool
BytecodeEmitter::updateLineNumberNotes(uint32_t offset)
{
TokenStream* ts = &parser->tokenStream;
bool onThisLine;
if (!ts->srcCoords.isOnThisLine(offset, currentLine(), &onThisLine))
return ts->reportError(JSMSG_OUT_OF_MEMORY);
if (!onThisLine) {
unsigned line = ts->srcCoords.lineNum(offset);
unsigned delta = line - currentLine();
/*
* Encode any change in the current source line number by using
* either several SRC_NEWLINE notes or just one SRC_SETLINE note,
* whichever consumes less space.
*
* NB: We handle backward line number deltas (possible with for
* loops where the update part is emitted after the body, but its
* line number is <= any line number in the body) here by letting
* unsigned delta_ wrap to a very large number, which triggers a
* SRC_SETLINE.
*/
current->currentLine = line;
current->lastColumn = 0;
if (delta >= LengthOfSetLine(line)) {
if (!newSrcNote2(SRC_SETLINE, ptrdiff_t(line)))
return false;
} else {
do {
if (!newSrcNote(SRC_NEWLINE))
return false;
} while (--delta != 0);
}
}
return true;
}
/* Updates the line number and column number information in the source notes. */
bool
BytecodeEmitter::updateSourceCoordNotes(uint32_t offset)
{
if (!updateLineNumberNotes(offset))
return false;
uint32_t columnIndex = parser->tokenStream.srcCoords.columnIndex(offset);
ptrdiff_t colspan = ptrdiff_t(columnIndex) - ptrdiff_t(current->lastColumn);
if (colspan != 0) {
// If the column span is so large that we can't store it, then just
// discard this information. This can happen with minimized or otherwise
// machine-generated code. Even gigantic column numbers are still
// valuable if you have a source map to relate them to something real;
// but it's better to fail soft here.
if (!SN_REPRESENTABLE_COLSPAN(colspan))
return true;
if (!newSrcNote2(SRC_COLSPAN, SN_COLSPAN_TO_OFFSET(colspan)))
return false;
current->lastColumn = columnIndex;
}
return true;
}
bool
BytecodeEmitter::emitLoopHead(ParseNode* nextpn)
{
if (nextpn) {
/*
* Try to give the JSOP_LOOPHEAD the same line number as the next
* instruction. nextpn is often a block, in which case the next
* instruction typically comes from the first statement inside.
*/
MOZ_ASSERT_IF(nextpn->isKind(PNK_STATEMENTLIST), nextpn->isArity(PN_LIST));
if (nextpn->isKind(PNK_STATEMENTLIST) && nextpn->pn_head)
nextpn = nextpn->pn_head;
if (!updateSourceCoordNotes(nextpn->pn_pos.begin))
return false;
}
return emit1(JSOP_LOOPHEAD);
}
bool
BytecodeEmitter::emitLoopEntry(ParseNode* nextpn)
{
if (nextpn) {
/* Update the line number, as for LOOPHEAD. */
MOZ_ASSERT_IF(nextpn->isKind(PNK_STATEMENTLIST), nextpn->isArity(PN_LIST));
if (nextpn->isKind(PNK_STATEMENTLIST) && nextpn->pn_head)
nextpn = nextpn->pn_head;
if (!updateSourceCoordNotes(nextpn->pn_pos.begin))
return false;
}
LoopStmtInfo* loop = LoopStmtInfo::fromStmtInfo(innermostStmt());
MOZ_ASSERT(loop->loopDepth > 0);
uint8_t loopDepthAndFlags = PackLoopEntryDepthHintAndFlags(loop->loopDepth, loop->canIonOsr);
return emit2(JSOP_LOOPENTRY, loopDepthAndFlags);
}
void
BytecodeEmitter::checkTypeSet(JSOp op)
{
if (CodeSpec[op].format & JOF_TYPESET) {
if (typesetCount < UINT16_MAX)
typesetCount++;
}
}
bool
BytecodeEmitter::emitUint16Operand(JSOp op, uint32_t operand)
{
MOZ_ASSERT(operand <= UINT16_MAX);
if (!emit3(op, UINT16_HI(operand), UINT16_LO(operand)))
return false;
checkTypeSet(op);
return true;
}
bool
BytecodeEmitter::emitUint32Operand(JSOp op, uint32_t operand)
{
ptrdiff_t off;
if (!emitN(op, 4, &off))
return false;
SET_UINT32(code(off), operand);
checkTypeSet(op);
return true;
}
bool
BytecodeEmitter::flushPops(int* npops)
{
MOZ_ASSERT(*npops != 0);
if (!emitUint16Operand(JSOP_POPN, *npops))
return false;
*npops = 0;
return true;
}
namespace {
class NonLocalExitScope {
BytecodeEmitter* bce;
const uint32_t savedScopeIndex;
const int savedDepth;
uint32_t openScopeIndex;
NonLocalExitScope(const NonLocalExitScope&) = delete;
public:
explicit NonLocalExitScope(BytecodeEmitter* bce_)
: bce(bce_),
savedScopeIndex(bce->blockScopeList.length()),
savedDepth(bce->stackDepth),
openScopeIndex(UINT32_MAX)
{
if (StmtInfoBCE* stmt = bce->innermostScopeStmt())
openScopeIndex = stmt->blockScopeIndex;
}
~NonLocalExitScope() {
for (uint32_t n = savedScopeIndex; n < bce->blockScopeList.length(); n++)
bce->blockScopeList.recordEnd(n, bce->offset(), bce->inPrologue());
bce->stackDepth = savedDepth;
}
bool popScopeForNonLocalExit(uint32_t blockScopeIndex) {
uint32_t scopeObjectIndex = bce->blockScopeList.findEnclosingScope(blockScopeIndex);
uint32_t parent = openScopeIndex;
if (!bce->blockScopeList.append(scopeObjectIndex, bce->offset(), bce->inPrologue(), parent))
return false;
openScopeIndex = bce->blockScopeList.length() - 1;
return true;
}
bool prepareForNonLocalJump(StmtInfoBCE* toStmt);
};
/*
* Emit additional bytecode(s) for non-local jumps.
*/
bool
NonLocalExitScope::prepareForNonLocalJump(StmtInfoBCE* toStmt)
{
int npops = 0;
#define FLUSH_POPS() if (npops && !bce->flushPops(&npops)) return false
for (StmtInfoBCE* stmt = bce->innermostStmt(); stmt != toStmt; stmt = stmt->enclosing) {
switch (stmt->type) {
case StmtType::FINALLY:
FLUSH_POPS();
if (!bce->emitBackPatchOp(&stmt->gosubs()))
return false;
break;
case StmtType::WITH:
if (!bce->emit1(JSOP_LEAVEWITH))
return false;
MOZ_ASSERT(stmt->linksScope());
if (!popScopeForNonLocalExit(stmt->blockScopeIndex))
return false;
break;
case StmtType::FOR_OF_LOOP:
npops += 2;
break;
case StmtType::FOR_IN_LOOP:
/* The iterator and the current value are on the stack. */
npops += 1;
FLUSH_POPS();
if (!bce->emit1(JSOP_ENDITER))
return false;
break;
case StmtType::SPREAD:
MOZ_ASSERT_UNREACHABLE("can't break/continue/return from inside a spread");
break;
case StmtType::SUBROUTINE:
/*
* There's a [exception or hole, retsub pc-index] pair and the
* possible return value on the stack that we need to pop.
*/
npops += 3;
break;
default:;
}
if (stmt->isBlockScope) {
StaticBlockObject& blockObj = stmt->staticBlock();
if (blockObj.needsClone()) {
if (!bce->emit1(JSOP_POPBLOCKSCOPE))
return false;
} else {
if (!bce->emit1(JSOP_DEBUGLEAVEBLOCK))
return false;
}
if (!popScopeForNonLocalExit(stmt->blockScopeIndex))
return false;
}
}
FLUSH_POPS();
return true;
#undef FLUSH_POPS
}
} // anonymous namespace
bool
BytecodeEmitter::emitGoto(StmtInfoBCE* toStmt, ptrdiff_t* lastp, SrcNoteType noteType)
{
NonLocalExitScope nle(this);
if (!nle.prepareForNonLocalJump(toStmt))
return false;
if (noteType != SRC_NULL) {
if (!newSrcNote(noteType))
return false;
}
return emitBackPatchOp(lastp);
}
void
BytecodeEmitter::backPatch(ptrdiff_t last, jsbytecode* target, jsbytecode op)
{
jsbytecode* pc = code(last);
jsbytecode* stop = code(-1);
while (pc != stop) {
ptrdiff_t delta = GET_JUMP_OFFSET(pc);
ptrdiff_t span = target - pc;
SET_JUMP_OFFSET(pc, span);
*pc = op;
pc -= delta;
}
}
void
BytecodeEmitter::pushStatementInner(StmtInfoBCE* stmt, StmtType type, ptrdiff_t top)
{
stmt->setTop(top);
stmtStack.push(stmt, type);
}
void
BytecodeEmitter::pushStatement(StmtInfoBCE* stmt, StmtType type, ptrdiff_t top)
{
pushStatementInner(stmt, type, top);
MOZ_ASSERT(!stmt->isLoop());
}
void
BytecodeEmitter::pushLoopStatement(LoopStmtInfo* stmt, StmtType type, ptrdiff_t top)
{
pushStatementInner(stmt, type, top);
MOZ_ASSERT(stmt->isLoop());
LoopStmtInfo* enclosingLoop = nullptr;
for (StmtInfoBCE* outer = stmt->enclosing; outer; outer = outer->enclosing) {
if (outer->isLoop()) {
enclosingLoop = LoopStmtInfo::fromStmtInfo(outer);
break;
}
}
stmt->stackDepth = this->stackDepth;
stmt->loopDepth = enclosingLoop ? enclosingLoop->loopDepth + 1 : 1;
int loopSlots;
if (type == StmtType::SPREAD)
loopSlots = 3;
else if (type == StmtType::FOR_IN_LOOP || type == StmtType::FOR_OF_LOOP)
loopSlots = 2;
else
loopSlots = 0;
MOZ_ASSERT(loopSlots <= stmt->stackDepth);
if (enclosingLoop) {
stmt->canIonOsr = (enclosingLoop->canIonOsr &&
stmt->stackDepth == enclosingLoop->stackDepth + loopSlots);
} else {
stmt->canIonOsr = stmt->stackDepth == loopSlots;
}
}
JSObject*
BytecodeEmitter::innermostStaticScope() const
{
if (StmtInfoBCE* stmt = innermostScopeStmt())
return stmt->staticScope;
return sc->staticScope();
}
#ifdef DEBUG
static bool
AllLocalsAliased(StaticBlockObject& obj)
{
for (unsigned i = 0; i < obj.numVariables(); i++)
if (!obj.isAliased(i))
return false;
return true;
}
#endif
bool
BytecodeEmitter::computeAliasedSlots(Handle<StaticBlockObject*> blockObj)
{
uint32_t numAliased = script->bindings.numAliasedBodyLevelLocals();
for (unsigned i = 0; i < blockObj->numVariables(); i++) {
Definition* dn = blockObj->definitionParseNode(i);
MOZ_ASSERT(dn->isDefn());
uint32_t index = dn->pn_scopecoord.slot();
uint32_t slot;
if (isAliasedName(this, dn)) {
slot = blockObj->blockIndexToSlot(index);
blockObj->setAliased(i, true);
} else {
// blockIndexToLocalIndex returns the frame slot following the
// unaliased locals. We add numAliased so that the slot value
// comes after all (aliased and unaliased) body level locals.
slot = numAliased + blockObj->blockIndexToLocalIndex(index);
blockObj->setAliased(i, false);
}
if (!dn->pn_scopecoord.setSlot(parser->tokenStream, slot))
return false;
#ifdef DEBUG
for (ParseNode* pnu = dn->dn_uses; pnu; pnu = pnu->pn_link) {
MOZ_ASSERT(pnu->pn_lexdef == dn);
MOZ_ASSERT(!(pnu->pn_dflags & PND_BOUND));
MOZ_ASSERT(pnu->pn_scopecoord.isFree());
}
#endif
}
MOZ_ASSERT_IF(sc->allLocalsAliased(), AllLocalsAliased(*blockObj));
return true;
}
void
BytecodeEmitter::computeLocalOffset(Handle<StaticBlockObject*> blockObj)
{
unsigned nbodyfixed = !sc->isGlobalContext()
? script->bindings.numUnaliasedBodyLevelLocals()
: 0;
unsigned localOffset = nbodyfixed;
if (StmtInfoBCE* stmt = innermostScopeStmt()) {
Rooted<NestedScopeObject*> outer(cx, stmt->staticScope);
for (; outer; outer = outer->enclosingNestedScope()) {
if (outer->is<StaticBlockObject>() && !IsStaticGlobalLexicalScope(outer)) {
StaticBlockObject& outerBlock = outer->as<StaticBlockObject>();
localOffset = outerBlock.localOffset() + outerBlock.numVariables();
break;
}
}
}
MOZ_ASSERT(localOffset + blockObj->numVariables()
<= nbodyfixed + script->bindings.numBlockScoped());
blockObj->setLocalOffset(localOffset);
}
// ~ Nested Scopes ~
//
// A nested scope is a region of a compilation unit (function, script, or eval
// code) with an additional node on the scope chain. This node may either be a
// "with" object or a "block" object. "With" objects represent "with" scopes.
// Block objects represent lexical scopes, and contain named block-scoped
// bindings, for example "let" bindings or the exception in a catch block.
// Those variables may be local and thus accessible directly from the stack, or
// "aliased" (accessed by name from nested functions, or dynamically via nested
// "eval" or "with") and only accessible through the scope chain.
//
// All nested scopes are present on the "static scope chain". A nested scope
// that is a "with" scope will be present on the scope chain at run-time as
// well. A block scope may or may not have a corresponding link on the run-time
// scope chain; if no variable declared in the block scope is "aliased", then no
// scope chain node is allocated.
//
// To help debuggers, the bytecode emitter arranges to record the PC ranges
// comprehended by a nested scope, and ultimately attach them to the JSScript.
// An element in the "block scope array" specifies the PC range, and links to a
// NestedScopeObject in the object list of the script. That scope object is
// linked to the previous link in the static scope chain, if any. The static
// scope chain at any pre-retire PC can be retrieved using
// JSScript::getStaticScope(jsbytecode* pc).
//
// Block scopes store their locals in the fixed part of a stack frame, after the
// "fixed var" bindings. A fixed var binding is a "var" or legacy "const"
// binding that occurs in a function (as opposed to a script or in eval code).
// Only functions have fixed var bindings.
//
// To assist the debugger, we emit a DEBUGLEAVEBLOCK opcode before leaving a
// block scope, if the block has no aliased locals. This allows DebugScopes
// to invalidate any association between a debugger scope object, which can
// proxy access to unaliased stack locals, and the actual live frame. In
// normal, non-debug mode, this opcode does not cause any baseline code to be
// emitted.
//
// If the block has aliased locals, no DEBUGLEAVEBLOCK is emitted, and
// POPBLOCKSCOPE itself balances the debug scope mapping. This gets around a
// comedic situation where DEBUGLEAVEBLOCK may remove a block scope from the
// debug scope map, but the immediate following POPBLOCKSCOPE adds it back due
// to an onStep hook.
//
// Enter a nested scope with enterNestedScope. It will emit
// PUSHBLOCKSCOPE/ENTERWITH if needed, and arrange to record the PC bounds of
// the scope. Leave a nested scope with leaveNestedScope, which, for blocks,
// will emit DEBUGLEAVEBLOCK and may emit POPBLOCKSCOPE. (For "with" scopes it
// emits LEAVEWITH, of course.) Pass enterNestedScope a fresh StmtInfoBCE
// object, and pass that same object to the corresponding leaveNestedScope. If
// the statement is a block scope, pass StmtType::BLOCK as stmtType; otherwise for
// with scopes pass StmtType::WITH.
//
bool
BytecodeEmitter::enterNestedScope(StmtInfoBCE* stmt, ObjectBox* objbox, StmtType stmtType)
{
Rooted<NestedScopeObject*> scopeObj(cx, &objbox->object->as<NestedScopeObject>());
uint32_t scopeObjectIndex = objectList.add(objbox);
switch (stmtType) {
case StmtType::BLOCK: {
Rooted<StaticBlockObject*> blockObj(cx, &scopeObj->as<StaticBlockObject>());
computeLocalOffset(blockObj);
if (!computeAliasedSlots(blockObj))
return false;
if (blockObj->needsClone()) {
if (!emitInternedObjectOp(scopeObjectIndex, JSOP_PUSHBLOCKSCOPE))
return false;
}
// Non-global block scopes are non-extensible. At this point the
// Parser has added all bindings to the StaticBlockObject, so we make
// it non-extensible.
if (!blockObj->makeNonExtensible(cx))
return false;
break;
}
case StmtType::WITH:
MOZ_ASSERT(scopeObj->is<StaticWithObject>());
if (!emitInternedObjectOp(scopeObjectIndex, JSOP_ENTERWITH))
return false;
break;
default:
MOZ_CRASH("Unexpected scope statement");
}
uint32_t parent = BlockScopeNote::NoBlockScopeIndex;
if (StmtInfoBCE* stmt = innermostScopeStmt())
parent = stmt->blockScopeIndex;
stmt->blockScopeIndex = blockScopeList.length();
if (!blockScopeList.append(scopeObjectIndex, offset(), inPrologue(), parent))
return false;
pushStatement(stmt, stmtType, offset());
scopeObj->initEnclosingScope(innermostStaticScope());
stmtStack.linkAsInnermostScopeStmt(stmt, *scopeObj);
MOZ_ASSERT(stmt->linksScope());
stmt->isBlockScope = (stmtType == StmtType::BLOCK);
return true;
}
// Patches |breaks| and |continues| unless the top statement info record
// represents a try-catch-finally suite.
void
BytecodeEmitter::popStatement()
{
if (!innermostStmt()->isTrying()) {
backPatch(innermostStmt()->breaks, code().end(), JSOP_GOTO);
backPatch(innermostStmt()->continues, code(innermostStmt()->update), JSOP_GOTO);
}
stmtStack.pop();
}
bool
BytecodeEmitter::leaveNestedScope(StmtInfoBCE* stmt)
{
MOZ_ASSERT(stmt == innermostScopeStmt());
MOZ_ASSERT(stmt->isBlockScope == !(stmt->type == StmtType::WITH));
uint32_t blockScopeIndex = stmt->blockScopeIndex;
#ifdef DEBUG
MOZ_ASSERT(blockScopeList.list[blockScopeIndex].length == 0);
uint32_t blockObjIndex = blockScopeList.list[blockScopeIndex].index;
ObjectBox* blockObjBox = objectList.find(blockObjIndex);
NestedScopeObject* staticScope = &blockObjBox->object->as<NestedScopeObject>();
MOZ_ASSERT(stmt->staticScope == staticScope);
MOZ_ASSERT_IF(!stmt->isBlockScope, staticScope->is<StaticWithObject>());
#endif
popStatement();
if (stmt->isBlockScope) {
if (stmt->staticScope->as<StaticBlockObject>().needsClone()) {
if (!emit1(JSOP_POPBLOCKSCOPE))
return false;
} else {
if (!emit1(JSOP_DEBUGLEAVEBLOCK))
return false;
}
} else {
if (!emit1(JSOP_LEAVEWITH))
return false;
}
blockScopeList.recordEnd(blockScopeIndex, offset(), inPrologue());
return true;
}
bool
BytecodeEmitter::emitIndex32(JSOp op, uint32_t index)
{
MOZ_ASSERT(checkStrictOrSloppy(op));
const size_t len = 1 + UINT32_INDEX_LEN;
MOZ_ASSERT(len == size_t(CodeSpec[op].length));