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Document (and assert) some of the safe-but-brittle implicit assumptions

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about references in the code generators.
Review URL: http://codereview.chromium.org/6301

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@453 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
kmillikin@chromium.org 2008-10-07 08:47:15 +00:00
parent c7c7b8b0e7
commit 5c80e6a83a
2 changed files with 105 additions and 59 deletions
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62
src/codegen-arm.cc
View File

@ -52,7 +52,8 @@ class ArmCodeGenerator;
class Reference BASE_EMBEDDED {
public:
enum Type { ILLEGAL = -1, EMPTY = 0, NAMED = 1, KEYED = 2 };
// The values of the types is important, see size().
enum Type { ILLEGAL = -1, SLOT = 0, NAMED = 1, KEYED = 2 };
Reference(ArmCodeGenerator* cgen, Expression* expression);
~Reference();
@ -62,9 +63,12 @@ class Reference BASE_EMBEDDED {
ASSERT(type_ == ILLEGAL);
type_ = value;
}
// The size of the reference or -1 if the reference is illegal.
int size() const { return type_; }
bool is_illegal() const { return type_ == ILLEGAL; }
bool is_slot() const { return type_ == SLOT; }
bool is_property() const { return type_ == NAMED || type_ == KEYED; }
private:
ArmCodeGenerator* cgen_;
@ -802,14 +806,17 @@ void ArmCodeGenerator::LoadReference(Reference* ref) {
Variable* var = e->AsVariableProxy()->AsVariable();
if (property != NULL) {
// The expression is either a property or a variable proxy that rewrites
// to a property.
Load(property->obj());
// Used a named reference if the key is a literal symbol.
// We don't use a named reference if they key is a string that can be
// legally parsed as an integer. This is because, otherwise we don't
// get into the slow case code that handles [] on String objects.
// We use a named reference if the key is a literal symbol, unless it is
// a string that can be legally parsed as an integer. This is because
// otherwise we will not get into the slow case code that handles [] on
// String objects.
Literal* literal = property->key()->AsLiteral();
uint32_t dummy;
if (literal != NULL && literal->handle()->IsSymbol() &&
if (literal != NULL &&
literal->handle()->IsSymbol() &&
!String::cast(*(literal->handle()))->AsArrayIndex(&dummy)) {
ref->set_type(Reference::NAMED);
} else {
@ -817,18 +824,19 @@ void ArmCodeGenerator::LoadReference(Reference* ref) {
ref->set_type(Reference::KEYED);
}
} else if (var != NULL) {
// The expression is a variable proxy that does not rewrite to a
// property. Global variables are treated as named property references.
if (var->is_global()) {
// global variable
LoadGlobal();
ref->set_type(Reference::NAMED);
} else {
// local variable
ref->set_type(Reference::EMPTY);
ASSERT(var->slot() != NULL);
ref->set_type(Reference::SLOT);
}
} else {
// Anything else is a runtime error.
Load(e);
__ CallRuntime(Runtime::kThrowReferenceError, 1);
__ push(r0);
}
}
@ -971,14 +979,13 @@ class InvokeBuiltinStub : public CodeStub {
void ArmCodeGenerator::GetReferenceProperty(Expression* key) {
ASSERT(!ref()->is_illegal());
Reference::Type type = ref()->type();
// TODO(1241834): Make sure that this it is safe to ignore the distinction
// between access types LOAD and LOAD_TYPEOF_EXPR. If there is a chance
// that reference errors can be thrown below, we must distinguish between
// the two kinds of loads (typeof expression loads must not throw a
// reference error).
if (type == Reference::NAMED) {
if (ref()->type() == Reference::NAMED) {
// Compute the name of the property.
Literal* literal = key->AsLiteral();
Handle<String> name(String::cast(*literal->handle()));
@ -997,7 +1004,7 @@ void ArmCodeGenerator::GetReferenceProperty(Expression* key) {
} else {
// Access keyed property.
ASSERT(type == Reference::KEYED);
ASSERT(ref()->type() == Reference::KEYED);
// TODO(1224671): Implement inline caching for keyed loads as on ia32.
GetPropertyStub stub;
@ -1460,9 +1467,13 @@ void ArmCodeGenerator::VisitDeclaration(Declaration* node) {
if (val != NULL) {
// Set initial value.
Reference target(this, node->proxy());
ASSERT(target.is_slot());
Load(val);
SetValue(&target);
// Get rid of the assigned value (declarations are statements).
// Get rid of the assigned value (declarations are statements). It's
// safe to pop the value lying on top of the reference before unloading
// the reference itself (which preserves the top of stack) because we
// know it is a zero-sized reference.
__ pop();
}
}
@ -1944,16 +1955,27 @@ void ArmCodeGenerator::VisitForInStatement(ForInStatement* node) {
{ Reference each(this, node->each());
if (!each.is_illegal()) {
if (each.size() > 0) {
// Reference's size is positive.
__ ldr(r0, MemOperand(sp, kPointerSize * each.size()));
__ push(r0);
}
// If the reference was to a slot we rely on the convenient property
// that it doesn't matter whether a value (eg, r3 pushed above) is
// right on top of or right underneath a zero-sized reference.
SetValue(&each);
if (each.size() > 0) {
__ pop(r0); // discard the value
// It's safe to pop the value lying on top of the reference before
// unloading the reference itself (which preserves the top of stack,
// ie, now the topmost value of the non-zero sized reference), since
// we will discard the top of stack after unloading the reference
// anyway.
__ pop(r0);
}
}
}
__ pop(); // pop the i'th entry pushed above
// Discard the i'th entry pushed above or else the remainder of the
// reference, whichever is currently on top of the stack.
__ pop();
CheckStack(); // TODO(1222600): ignore if body contains calls.
__ jmp(&loop);
@ -1981,11 +2003,11 @@ void ArmCodeGenerator::VisitTryCatch(TryCatch* node) {
// Store the caught exception in the catch variable.
__ push(r0);
{ Reference ref(this, node->catch_var());
// Load the exception to the top of the stack.
__ ldr(r0, MemOperand(sp, ref.size() * kPointerSize));
__ push(r0);
ASSERT(ref.is_slot());
// Here we make use of the convenient property that it doesn't matter
// whether a value is immediately on top of or underneath a zero-sized
// reference.
SetValue(&ref);
__ pop(r0);
}
// Remove the exception from the stack.

82
src/codegen-ia32.cc
View File

@ -58,7 +58,8 @@ enum OverwriteMode { NO_OVERWRITE, OVERWRITE_LEFT, OVERWRITE_RIGHT };
class Reference BASE_EMBEDDED {
public:
enum Type { ILLEGAL = -1, EMPTY = 0, NAMED = 1, KEYED = 2 };
// The values of the types is important, see size().
enum Type { ILLEGAL = -1, SLOT = 0, NAMED = 1, KEYED = 2 };
Reference(Ia32CodeGenerator* cgen, Expression* expression);
~Reference();
@ -68,9 +69,13 @@ class Reference BASE_EMBEDDED {
ASSERT(type_ == ILLEGAL);
type_ = value;
}
// The size of the reference or -1 if the reference is illegal.
int size() const { return type_; }
bool is_illegal() const { return type_ == ILLEGAL; }
bool is_slot() const { return type_ == SLOT; }
bool is_property() const { return type_ == NAMED || type_ == KEYED; }
private:
Ia32CodeGenerator* cgen_;
@ -653,18 +658,18 @@ void Ia32CodeGenerator::GenCode(FunctionLiteral* fun) {
ASSERT(scope->arguments_shadow() != NULL);
Comment cmnt(masm_, "[ store arguments object");
{ Reference shadow_ref(this, scope->arguments_shadow());
ASSERT(shadow_ref.is_slot());
{ Reference arguments_ref(this, scope->arguments());
ASSERT(arguments_ref.is_slot());
// If the newly-allocated arguments object is already on the
// stack, we make use of the property that references representing
// variables take up no space on the expression stack (ie, it
// doesn't matter that the stored value is actually below the
// reference).
ASSERT(arguments_ref.size() == 0);
ASSERT(shadow_ref.size() == 0);
// If the newly-allocated argument object is not already on the
// stack, we rely on the property that loading a
// (zero-sized) reference will not clobber the ecx register.
// stack, we make use of the convenient property that references
// representing slots take up no space on the expression stack
// (ie, it doesn't matter that the stored value is actually below
// the reference).
//
// If the newly-allocated argument object is not already on
// the stack, we rely on the property that loading a
// zero-sized reference will not clobber the ecx register.
if (!arguments_object_saved) {
__ push(ecx);
}
@ -845,14 +850,17 @@ void Ia32CodeGenerator::LoadReference(Reference* ref) {
Variable* var = e->AsVariableProxy()->AsVariable();
if (property != NULL) {
// The expression is either a property or a variable proxy that rewrites
// to a property.
Load(property->obj());
// Used a named reference if the key is a literal symbol.
// We don't use a named reference if they key is a string that can be
// legally parsed as an integer. This is because, otherwise we don't
// get into the slow case code that handles [] on String objects.
// We use a named reference if the key is a literal symbol, unless it is
// a string that can be legally parsed as an integer. This is because
// otherwise we will not get into the slow case code that handles [] on
// String objects.
Literal* literal = property->key()->AsLiteral();
uint32_t dummy;
if (literal != NULL && literal->handle()->IsSymbol() &&
if (literal != NULL &&
literal->handle()->IsSymbol() &&
!String::cast(*(literal->handle()))->AsArrayIndex(&dummy)) {
ref->set_type(Reference::NAMED);
} else {
@ -860,18 +868,19 @@ void Ia32CodeGenerator::LoadReference(Reference* ref) {
ref->set_type(Reference::KEYED);
}
} else if (var != NULL) {
// The expression is a variable proxy that does not rewrite to a
// property. Global variables are treated as named property references.
if (var->is_global()) {
// global variable
LoadGlobal();
ref->set_type(Reference::NAMED);
} else {
// local variable
ref->set_type(Reference::EMPTY);
ASSERT(var->slot() != NULL);
ref->set_type(Reference::SLOT);
}
} else {
// Anything else is a runtime error.
Load(e);
__ CallRuntime(Runtime::kThrowReferenceError, 1);
__ push(eax);
}
}
@ -959,14 +968,13 @@ void Ia32CodeGenerator::ToBoolean(Label* true_target, Label* false_target) {
void Ia32CodeGenerator::GetReferenceProperty(Expression* key) {
ASSERT(!ref()->is_illegal());
Reference::Type type = ref()->type();
// TODO(1241834): Make sure that this it is safe to ignore the distinction
// between access types LOAD and LOAD_TYPEOF_EXPR. If there is a chance
// that reference errors can be thrown below, we must distinguish between
// the two kinds of loads (typeof expression loads must not throw a
// reference error).
if (type == Reference::NAMED) {
if (ref()->type() == Reference::NAMED) {
// Compute the name of the property.
Literal* literal = key->AsLiteral();
Handle<String> name(String::cast(*literal->handle()));
@ -983,7 +991,7 @@ void Ia32CodeGenerator::GetReferenceProperty(Expression* key) {
}
} else {
// Access keyed property.
ASSERT(type == Reference::KEYED);
ASSERT(ref()->type() == Reference::KEYED);
// Call IC code.
Handle<Code> ic(Builtins::builtin(Builtins::KeyedLoadIC_Initialize));
@ -1753,9 +1761,13 @@ void Ia32CodeGenerator::VisitDeclaration(Declaration* node) {
if (val != NULL) {
// Set initial value.
Reference target(this, node->proxy());
ASSERT(target.is_slot());
Load(val);
SetValue(&target);
// Get rid of the assigned value (declarations are statements).
// Get rid of the assigned value (declarations are statements). It's
// safe to pop the value lying on top of the reference before unloading
// the reference itself (which preserves the top of stack) because we
// know that it is a zero-sized reference.
__ pop(eax); // Pop(no_reg);
}
}
@ -2269,19 +2281,29 @@ void Ia32CodeGenerator::VisitForInStatement(ForInStatement* node) {
// Store the entry in the 'each' expression and take another spin in the loop.
// edx: i'th entry of the enum cache (or string there of)
__ push(Operand(ebx));
__ push(ebx);
{ Reference each(this, node->each());
if (!each.is_illegal()) {
if (each.size() > 0) {
__ push(Operand(esp, kPointerSize * each.size()));
}
// If the reference was to a slot we rely on the convenient property
// that it doesn't matter whether a value (eg, ebx pushed above) is
// right on top of or right underneath a zero-sized reference.
SetValue(&each);
if (each.size() > 0) {
// It's safe to pop the value lying on top of the reference before
// unloading the reference itself (which preserves the top of stack,
// ie, now the topmost value of the non-zero sized reference), since
// we will discard the top of stack after unloading the reference
// anyway.
__ pop(eax);
}
}
}
__ pop(eax); // pop the i'th entry pushed above
// Discard the i'th entry pushed above or else the remainder of the
// reference, whichever is currently on top of the stack.
__ pop(eax);
CheckStack(); // TODO(1222600): ignore if body contains calls.
__ jmp(&loop);
@ -2308,10 +2330,11 @@ void Ia32CodeGenerator::VisitTryCatch(TryCatch* node) {
// Store the caught exception in the catch variable.
{ Reference ref(this, node->catch_var());
// Load the exception to the top of the stack.
__ push(Operand(esp, ref.size() * kPointerSize));
ASSERT(ref.is_slot());
// Load the exception to the top of the stack. Here we make use of the
// convenient property that it doesn't matter whether a value is
// immediately on top of or underneath a zero-sized reference.
SetValue(&ref);
__ pop(eax); // pop the pushed exception
}
// Remove the exception from the stack.
@ -3051,6 +3074,7 @@ void Ia32CodeGenerator::VisitCall(Call* node) {
GetValue(&ref);
// Pass receiver to called function.
// The reference's size is non-negative.
__ push(Operand(esp, ref.size() * kPointerSize));
// Call the function.