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Remove some initialization checks based on source positions.

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This depends on
http://codereview.chromium.org/8352039 and
http://codereview.chromium.org/8423005 .

Review URL: http://codereview.chromium.org/8422010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9870 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
keuchel@chromium.org 2011-11-03 12:05:48 +00:00
parent 58123bff56
commit fd21937812
6 changed files with 165 additions and 59 deletions
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38
src/arm/full-codegen-arm.cc
View File

@ -1283,9 +1283,38 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
Comment cmnt(masm_, var->IsContextSlot()
? "Context variable"
: "Stack variable");
if (!var->binding_needs_init()) {
context()->Plug(var);
} else {
if (var->binding_needs_init()) {
// var->scope() may be NULL when the proxy is located in eval code and
// refers to a potential outside binding. Currently those bindings are
// always looked up dynamically, i.e. in that case
// var->location() == LOOKUP.
// always holds.
ASSERT(var->scope() != NULL);
// Check if the binding really needs an initialization check. The check
// can be skipped in the following situation: we have a LET or CONST
// binding in harmony mode, both the Variable and the VariableProxy have
// the same declaration scope (i.e. they are both in global code, in the
// same function or in the same eval code) and the VariableProxy is in
// the source physically located after the initializer of the variable.
//
// We cannot skip any initialization checks for CONST in non-harmony
// mode because const variables may be declared but never initialized:
// if (false) { const x; }; var y = x;
//
// The condition on the declaration scopes is a conservative check for
// nested functions that access a binding and are called before the
// binding is initialized:
// function() { f(); let x = 1; function f() { x = 2; } }
//
// Check that we always have valid source position.
ASSERT(var->initializer_position() != RelocInfo::kNoPosition);
ASSERT(proxy->position() != RelocInfo::kNoPosition);
bool skip_init_check =
var->mode() != CONST &&
var->scope()->DeclarationScope() == scope()->DeclarationScope() &&
var->initializer_position() < proxy->position();
if (!skip_init_check) {
// Let and const need a read barrier.
GetVar(r0, var);
__ CompareRoot(r0, Heap::kTheHoleValueRootIndex);
@ -1304,7 +1333,10 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
__ LoadRoot(r0, Heap::kUndefinedValueRootIndex, eq);
}
context()->Plug(r0);
break;
}
}
context()->Plug(var);
break;
}

38
src/ia32/full-codegen-ia32.cc
View File

@ -1234,9 +1234,38 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
Comment cmnt(masm_, var->IsContextSlot()
? "Context variable"
: "Stack variable");
if (!var->binding_needs_init()) {
context()->Plug(var);
} else {
if (var->binding_needs_init()) {
// var->scope() may be NULL when the proxy is located in eval code and
// refers to a potential outside binding. Currently those bindings are
// always looked up dynamically, i.e. in that case
// var->location() == LOOKUP.
// always holds.
ASSERT(var->scope() != NULL);
// Check if the binding really needs an initialization check. The check
// can be skipped in the following situation: we have a LET or CONST
// binding in harmony mode, both the Variable and the VariableProxy have
// the same declaration scope (i.e. they are both in global code, in the
// same function or in the same eval code) and the VariableProxy is in
// the source physically located after the initializer of the variable.
//
// We cannot skip any initialization checks for CONST in non-harmony
// mode because const variables may be declared but never initialized:
// if (false) { const x; }; var y = x;
//
// The condition on the declaration scopes is a conservative check for
// nested functions that access a binding and are called before the
// binding is initialized:
// function() { f(); let x = 1; function f() { x = 2; } }
//
// Check that we always have valid source position.
ASSERT(var->initializer_position() != RelocInfo::kNoPosition);
ASSERT(proxy->position() != RelocInfo::kNoPosition);
bool skip_init_check =
var->mode() != CONST &&
var->scope()->DeclarationScope() == scope()->DeclarationScope() &&
var->initializer_position() < proxy->position();
if (!skip_init_check) {
// Let and const need a read barrier.
Label done;
GetVar(eax, var);
@ -1254,7 +1283,10 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
}
__ bind(&done);
context()->Plug(eax);
break;
}
}
context()->Plug(var);
break;
}

7
src/parser.cc
View File

@ -1773,7 +1773,7 @@ Block* Parser::ParseVariableDeclarations(
// For let/const declarations in harmony mode, we can also immediately
// pre-resolve the proxy because it resides in the same scope as the
// declaration.
Declare(name, mode, NULL, mode != VAR, CHECK_OK);
VariableProxy* proxy = Declare(name, mode, NULL, mode != VAR, CHECK_OK);
nvars++;
if (declaration_scope->num_var_or_const() > kMaxNumFunctionLocals) {
ReportMessageAt(scanner().location(), "too_many_variables",
@ -1828,6 +1828,11 @@ Block* Parser::ParseVariableDeclarations(
if (decl_props != NULL) *decl_props = kHasInitializers;
}
// Record the end position of the initializer.
if (proxy->var() != NULL) {
proxy->var()->set_initializer_position(scanner().location().end_pos);
}
// Make sure that 'const x' and 'let x' initialize 'x' to undefined.
if (value == NULL && needs_init) {
value = GetLiteralUndefined();

1
src/variables.cc
View File

@ -66,6 +66,7 @@ Variable::Variable(Scope* scope,
kind_(kind),
location_(UNALLOCATED),
index_(-1),
initializer_position_(RelocInfo::kNoPosition),
local_if_not_shadowed_(NULL),
is_valid_LHS_(is_valid_LHS),
is_accessed_from_inner_scope_(false),

4
src/variables.h
View File

@ -103,6 +103,9 @@ class Variable: public ZoneObject {
bool is_used() { return is_used_; }
void set_is_used(bool flag) { is_used_ = flag; }
int initializer_position() { return initializer_position_; }
void set_initializer_position(int pos) { initializer_position_ = pos; }
bool IsVariable(Handle<String> n) const {
return !is_this() && name().is_identical_to(n);
}
@ -163,6 +166,7 @@ class Variable: public ZoneObject {
Kind kind_;
Location location_;
int index_;
int initializer_position_;
// If this field is set, this variable references the stored locally bound
// variable, but it might be shadowed by variable bindings introduced by

38
src/x64/full-codegen-x64.cc
View File

@ -1240,9 +1240,38 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
case Variable::LOCAL:
case Variable::CONTEXT: {
Comment cmnt(masm_, var->IsContextSlot() ? "Context slot" : "Stack slot");
if (!var->binding_needs_init()) {
context()->Plug(var);
} else {
if (var->binding_needs_init()) {
// var->scope() may be NULL when the proxy is located in eval code and
// refers to a potential outside binding. Currently those bindings are
// always looked up dynamically, i.e. in that case
// var->location() == LOOKUP.
// always holds.
ASSERT(var->scope() != NULL);
// Check if the binding really needs an initialization check. The check
// can be skipped in the following situation: we have a LET or CONST
// binding in harmony mode, both the Variable and the VariableProxy have
// the same declaration scope (i.e. they are both in global code, in the
// same function or in the same eval code) and the VariableProxy is in
// the source physically located after the initializer of the variable.
//
// We cannot skip any initialization checks for CONST in non-harmony
// mode because const variables may be declared but never initialized:
// if (false) { const x; }; var y = x;
//
// The condition on the declaration scopes is a conservative check for
// nested functions that access a binding and are called before the
// binding is initialized:
// function() { f(); let x = 1; function f() { x = 2; } }
//
// Check that we always have valid source position.
ASSERT(var->initializer_position() != RelocInfo::kNoPosition);
ASSERT(proxy->position() != RelocInfo::kNoPosition);
bool skip_init_check =
var->mode() != CONST &&
var->scope()->DeclarationScope() == scope()->DeclarationScope() &&
var->initializer_position() < proxy->position();
if (!skip_init_check) {
// Let and const need a read barrier.
Label done;
GetVar(rax, var);
@ -1260,7 +1289,10 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
}
__ bind(&done);
context()->Plug(rax);
break;
}
}
context()->Plug(var);
break;
}