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Bug 1147371: Implement IteratorClose for array destructuring
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Issue #74
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@janekptacijarabaci
janekptacijarabaci committed Mar 24, 2018
1 parent 4b487ef commit 2bb0252
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Showing 7 changed files with 322 additions and 135 deletions.
218 changes: 126 additions & 92 deletions js/src/frontend/BytecodeEmitter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4947,7 +4947,7 @@ BytecodeEmitter::emitIteratorClose(Maybe<JumpTarget> yieldStarTryStart, bool all

template <typename InnerEmitter>
bool
BytecodeEmitter::wrapWithIteratorCloseTryNote(int32_t iterDepth, InnerEmitter emitter)
BytecodeEmitter::wrapWithDestructuringIteratorCloseTryNote(int32_t iterDepth, InnerEmitter emitter)
{
MOZ_ASSERT(this->stackDepth >= iterDepth);

Expand All @@ -4956,7 +4956,7 @@ BytecodeEmitter::wrapWithIteratorCloseTryNote(int32_t iterDepth, InnerEmitter em
return false;
ptrdiff_t end = offset();
if (start != end)
return tryNoteList.append(JSTRY_ITERCLOSE, iterDepth, start, end);
return tryNoteList.append(JSTRY_DESTRUCTURING_ITERCLOSE, iterDepth, start, end);
return true;
}

Expand Down Expand Up @@ -5057,14 +5057,17 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav

// Here's pseudo code for |let [a, b, , c=y, ...d] = x;|
//
// Lines that are annotated "covered by trynote" mean that upon throwing
// an exception, IteratorClose is called on iter only if done is false.
//
// let x, y;
// let a, b, c, d;
// let iter, lref, result, done, value; // stack values
//
// iter = x[Symbol.iterator]();
//
// // ==== emitted by loop for a ====
// lref = GetReference(a);
// lref = GetReference(a); // covered by trynote
//
// result = iter.next();
// done = result.done;
Expand All @@ -5074,10 +5077,10 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
// else
// value = result.value;
//
// SetOrInitialize(lref, value);
// SetOrInitialize(lref, value); // covered by trynote
//
// // ==== emitted by loop for b ====
// lref = GetReference(b);
// lref = GetReference(b); // covered by trynote
//
// if (done) {
// value = undefined;
Expand All @@ -5090,7 +5093,7 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
// value = result.value;
// }
//
// SetOrInitialize(lref, value);
// SetOrInitialize(lref, value); // covered by trynote
//
// // ==== emitted by loop for elision ====
// if (done) {
Expand All @@ -5105,7 +5108,7 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
// }
//
// // ==== emitted by loop for c ====
// lref = GetReference(c);
// lref = GetReference(c); // covered by trynote
//
// if (done) {
// value = undefined;
Expand All @@ -5119,19 +5122,23 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
// }
//
// if (value === undefined)
// value = y;
// value = y; // covered by trynote
//
// SetOrInitialize(lref, value);
// SetOrInitialize(lref, value); // covered by trynote
//
// // ==== emitted by loop for d ====
// lref = GetReference(d);
// lref = GetReference(d); // covered by trynote
//
// if (done)
// value = [];
// else
// value = [...iter];
//
// SetOrInitialize(lref, value);
// SetOrInitialize(lref, value); // covered by trynote
//
// // === emitted after loop ===
// if (!done)
// IteratorClose(iter);

// Use an iterator to destructure the RHS, instead of index lookup. We
// must leave the *original* value on the stack.
Expand All @@ -5140,25 +5147,61 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
if (!emitIterator()) // ... OBJ ITER
return false;

// For an empty pattern [], call IteratorClose unconditionally. Nothing
// else needs to be done.
if (!pattern->pn_head)
return emitIteratorClose(); // ... OBJ

// Push an initial FALSE value for DONE.
if (!emit1(JSOP_FALSE)) // ... OBJ ITER FALSE
return false;

// JSTRY_DESTRUCTURING_ITERCLOSE expects the iterator and the done value
// to be the second to top and the top of the stack, respectively.
// IteratorClose is called upon exception only if done is false.
int32_t tryNoteDepth = stackDepth;

for (ParseNode* member = pattern->pn_head; member; member = member->pn_next) {
bool isHead = member == pattern->pn_head;
bool hasNext = !!member->pn_next;
bool isFirst = member == pattern->pn_head;
DebugOnly<bool> hasNext = !!member->pn_next;

if (member->isKind(PNK_SPREAD)) {
size_t emitted = 0;
if (!emitDestructuringLHSRef(member, &emitted)) // ... OBJ ITER ?DONE *LREF
size_t emitted = 0;

// Spec requires LHS reference to be evaluated first.
ParseNode* lhsPattern = member;
if (lhsPattern->isKind(PNK_ASSIGN))
lhsPattern = lhsPattern->pn_left;

bool isElision = lhsPattern->isKind(PNK_ELISION);
if (!isElision) {
auto emitLHSRef = [lhsPattern, &emitted](BytecodeEmitter* bce) {
return bce->emitDestructuringLHSRef(lhsPattern, &emitted); // ... OBJ ITER DONE *LREF
};
if (!wrapWithDestructuringIteratorCloseTryNote(tryNoteDepth, emitLHSRef))
return false;
}

// Pick the DONE value to the top of the stack.
if (emitted) {
if (!emit2(JSOP_PICK, emitted)) // ... OBJ ITER *LREF DONE
return false;
}

if (isFirst) {
// If this element is the first, DONE is always FALSE, so pop it.
//
// Non-first elements should emit if-else depending on the
// member pattern, below.
if (!emit1(JSOP_POP)) // ... OBJ ITER *LREF
return false;
}

if (member->isKind(PNK_SPREAD)) {
IfThenElseEmitter ifThenElse(this);
if (!isHead) {
if (!isFirst) {
// If spread is not the first element of the pattern,
// iterator can already be completed.
// ... OBJ ITER DONE *LREF
if (emitted) {
if (!emit2(JSOP_PICK, emitted)) // ... OBJ ITER *LREF DONE
return false;
}

// ... OBJ ITER *LREF DONE
if (!ifThenElse.emitIfElse()) // ... OBJ ITER *LREF
return false;

Expand All @@ -5181,77 +5224,53 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
if (!emit1(JSOP_POP)) // ... OBJ ITER *LREF ARRAY
return false;

if (!isHead) {
if (!isFirst) {
if (!ifThenElse.emitEnd())
return false;
MOZ_ASSERT(ifThenElse.pushed() == 1);
}

if (!emitSetOrInitializeDestructuring(member, flav)) // ... OBJ ITER
// At this point the iterator is done. Unpick a TRUE value for DONE above ITER.
if (!emit1(JSOP_TRUE)) // ... OBJ ITER *LREF ARRAY TRUE
return false;
if (!emit2(JSOP_UNPICK, emitted + 1)) // ... OBJ ITER TRUE *LREF ARRAY
return false;

auto emitAssignment = [member, flav](BytecodeEmitter* bce) {
return bce->emitSetOrInitializeDestructuring(member, flav); // ... OBJ ITER TRUE
};
if (!wrapWithDestructuringIteratorCloseTryNote(tryNoteDepth, emitAssignment))
return false;

MOZ_ASSERT(!hasNext);
break;
}

ParseNode* pndefault = nullptr;
ParseNode* subpattern = member;
if (subpattern->isKind(PNK_ASSIGN)) {
pndefault = subpattern->pn_right;
subpattern = subpattern->pn_left;
}

bool isElision = subpattern->isKind(PNK_ELISION);

MOZ_ASSERT(!subpattern->isKind(PNK_SPREAD));
if (member->isKind(PNK_ASSIGN))
pndefault = member->pn_right;

size_t emitted = 0;
if (!isElision) {
if (!emitDestructuringLHSRef(subpattern, &emitted)) // ... OBJ ITER ?DONE *LREF
return false;
}
MOZ_ASSERT(!member->isKind(PNK_SPREAD));

IfThenElseEmitter ifAlreadyDone(this);
if (!isHead) {
// If this element is not the first element of the pattern,
// iterator can already be completed.
// ... OBJ ITER DONE *LREF
if (emitted) {
if (hasNext) {
if (!emitDupAt(emitted)) // ... OBJ ITER DONE *LREF DONE
return false;
} else {
if (!emit2(JSOP_PICK, emitted)) // ... OBJ ITER *LREF DONE
return false;
}
} else {
if (hasNext) {
// The position of LREF in the following stack comment
// isn't accurate for the operation, but it's equivalent
// since LREF is nothing
if (!emit1(JSOP_DUP)) // ... OBJ ITER DONE *LREF DONE
return false;
}
}
if (!ifAlreadyDone.emitIfElse()) // ... OBJ ITER ?DONE *LREF
if (!isFirst) {
// ... OBJ ITER *LREF DONE
if (!ifAlreadyDone.emitIfElse()) // ... OBJ ITER *LREF
return false;

if (!emit1(JSOP_UNDEFINED)) // ... OBJ ITER ?DONE *LREF UNDEF
if (!emit1(JSOP_UNDEFINED)) // ... OBJ ITER *LREF UNDEF
return false;
if (!emit1(JSOP_NOP_DESTRUCTURING)) // ... OBJ ITER ?DONE *LREF UNDEF
if (!emit1(JSOP_NOP_DESTRUCTURING)) // ... OBJ ITER *LREF UNDEF
return false;

if (!ifAlreadyDone.emitElse()) // ... OBJ ITER ?DONE *LREF
// The iterator is done. Unpick a TRUE value for DONE above ITER.
if (!emit1(JSOP_TRUE)) // ... OBJ ITER *LREF UNDEF TRUE
return false;
if (!emit2(JSOP_UNPICK, emitted + 1)) // ... OBJ ITER TRUE *LREF UNDEF
return false;

if (hasNext) {
if (emitted) {
if (!emit2(JSOP_PICK, emitted)) // ... OBJ ITER *LREF DONE
return false;
}
if (!emit1(JSOP_POP)) // ... OBJ ITER *LREF
return false;
}
if (!ifAlreadyDone.emitElse()) // ... OBJ ITER *LREF
return false;
}

if (emitted) {
Expand All @@ -5268,59 +5287,74 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
if (!emitAtomOp(cx->names().done, JSOP_GETPROP)) // ... OBJ ITER *LREF RESULT DONE
return false;

if (hasNext) {
if (!emit1(JSOP_DUP)) // ... OBJ ITER *LREF RESULT DONE DONE
return false;
if (!emit2(JSOP_UNPICK, emitted + 2)) // ... OBJ ITER DONE *LREF RESULT DONE
return false;
}
if (!emit1(JSOP_DUP)) // ... OBJ ITER *LREF RESULT DONE DONE
return false;
if (!emit2(JSOP_UNPICK, emitted + 2)) // ... OBJ ITER DONE *LREF RESULT DONE
return false;

IfThenElseEmitter ifDone(this);
if (!ifDone.emitIfElse()) // ... OBJ ITER ?DONE *LREF RESULT
if (!ifDone.emitIfElse()) // ... OBJ ITER DONE *LREF RESULT
return false;

if (!emit1(JSOP_POP)) // ... OBJ ITER ?DONE *LREF
if (!emit1(JSOP_POP)) // ... OBJ ITER DONE *LREF
return false;
if (!emit1(JSOP_UNDEFINED)) // ... OBJ ITER ?DONE *LREF UNDEF
if (!emit1(JSOP_UNDEFINED)) // ... OBJ ITER DONE *LREF UNDEF
return false;
if (!emit1(JSOP_NOP_DESTRUCTURING)) // ... OBJ ITER ?DONE *LREF UNDEF
if (!emit1(JSOP_NOP_DESTRUCTURING)) // ... OBJ ITER DONE *LREF UNDEF
return false;

if (!ifDone.emitElse()) // ... OBJ ITER ?DONE *LREF RESULT
if (!ifDone.emitElse()) // ... OBJ ITER DONE *LREF RESULT
return false;

if (!emitAtomOp(cx->names().value, JSOP_GETPROP)) // ... OBJ ITER ?DONE *LREF VALUE
if (!emitAtomOp(cx->names().value, JSOP_GETPROP)) // ... OBJ ITER DONE *LREF VALUE
return false;

if (!ifDone.emitEnd())
return false;
MOZ_ASSERT(ifDone.pushed() == 0);

if (!isHead) {
if (!isFirst) {
if (!ifAlreadyDone.emitEnd())
return false;
MOZ_ASSERT(ifAlreadyDone.pushed() == 1);
MOZ_ASSERT(ifAlreadyDone.pushed() == 2);
}

if (pndefault) {
if (!emitDefault(pndefault, subpattern)) // ... OBJ ITER ?DONE *LREF VALUE
auto emitDefault = [pndefault, lhsPattern](BytecodeEmitter* bce) {
return bce->emitDefault(pndefault, lhsPattern); // ... OBJ ITER DONE *LREF VALUE
};

if (!wrapWithDestructuringIteratorCloseTryNote(tryNoteDepth, emitDefault))
return false;
}

if (!isElision) {
if (!emitSetOrInitializeDestructuring(subpattern,
flav)) // ... OBJ ITER ?DONE
{
auto emitAssignment = [lhsPattern, flav](BytecodeEmitter* bce) {
return bce->emitSetOrInitializeDestructuring(lhsPattern, flav); // ... OBJ ITER DONE
};

if (!wrapWithDestructuringIteratorCloseTryNote(tryNoteDepth, emitAssignment))
return false;
}
} else {
if (!emit1(JSOP_POP)) // ... OBJ ITER ?DONE
if (!emit1(JSOP_POP)) // ... OBJ ITER DONE
return false;
}
}

// The last DONE value is on top of the stack. If not DONE, call
// IteratorClose.
// ... OBJ ITER DONE
IfThenElseEmitter ifDone(this);
if (!ifDone.emitIfElse()) // ... OBJ ITER
return false;
if (!emit1(JSOP_POP)) // ... OBJ
return false;
if (!ifDone.emitElse()) // ... OBJ ITER
return false;
if (!emitIteratorClose()) // ... OBJ
return false;
if (!ifDone.emitEnd())
return false;

return true;
}
Expand Down
3 changes: 2 additions & 1 deletion js/src/frontend/BytecodeEmitter.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -684,7 +684,8 @@ struct MOZ_STACK_CLASS BytecodeEmitter
bool allowSelfHosted = false);

template <typename InnerEmitter>
MOZ_MUST_USE bool wrapWithIteratorCloseTryNote(int32_t iterDepth, InnerEmitter emitter);
MOZ_MUST_USE bool wrapWithDestructuringIteratorCloseTryNote(int32_t iterDepth,
InnerEmitter emitter);

// Check if the value on top of the stack is "undefined". If so, replace
// that value on the stack with the value defined by |defaultExpr|.
Expand Down
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