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MIPS: Remove some initialization checks based on source positions.

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Port r9870 (959ec43).

Original commit message:

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

BUG=
TEST=

Review URL: http://codereview.chromium.org/8467007
Patch from Gergely Kis <gergely@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9887 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
keuchel@chromium.org 2011-11-07 09:42:54 +00:00
parent 086ae44213
commit aad9e50fb4
1 changed files with 54 additions and 22 deletions
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76
src/mips/full-codegen-mips.cc
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@ -1289,30 +1289,62 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
Comment cmnt(masm_, var->IsContextSlot()
? "Context variable"
: "Stack variable");
if (!var->binding_needs_init()) {
context()->Plug(var);
} else {
// Let and const need a read barrier.
GetVar(v0, var);
__ LoadRoot(at, Heap::kTheHoleValueRootIndex);
__ subu(at, v0, at); // Sub as compare: at == 0 on eq.
if (var->mode() == LET || var->mode() == CONST_HARMONY) {
// Throw a reference error when using an uninitialized let/const
// binding in harmony mode.
Label done;
__ Branch(&done, ne, at, Operand(zero_reg));
__ li(a0, Operand(var->name()));
__ push(a0);
__ CallRuntime(Runtime::kThrowReferenceError, 1);
__ bind(&done);
} else {
// Uninitalized const bindings outside of harmony mode are unholed.
ASSERT(var->mode() == CONST);
__ LoadRoot(a0, Heap::kUndefinedValueRootIndex);
__ movz(v0, a0, at); // Conditional move: Undefined if TheHole.
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(v0, var);
__ LoadRoot(at, Heap::kTheHoleValueRootIndex);
__ subu(at, v0, at); // Sub as compare: at == 0 on eq.
if (var->mode() == LET || var->mode() == CONST_HARMONY) {
// Throw a reference error when using an uninitialized let/const
// binding in harmony mode.
Label done;
__ Branch(&done, ne, at, Operand(zero_reg));
__ li(a0, Operand(var->name()));
__ push(a0);
__ CallRuntime(Runtime::kThrowReferenceError, 1);
__ bind(&done);
} else {
// Uninitalized const bindings outside of harmony mode are unholed.
ASSERT(var->mode() == CONST);
__ LoadRoot(a0, Heap::kUndefinedValueRootIndex);
__ movz(v0, a0, at); // Conditional move: Undefined if TheHole.
}
context()->Plug(v0);
break;
}
context()->Plug(v0);
}
context()->Plug(var);
break;
}