Revision: 9887
Author: [email protected]
Date: Mon Nov 7 01:42:54 2011
Log: MIPS: Remove some initialization checks based on source positions.
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 <[email protected]>.
http://code.google.com/p/v8/source/detail?r=9887
Modified:
/branches/bleeding_edge/src/mips/full-codegen-mips.cc
=======================================
--- /branches/bleeding_edge/src/mips/full-codegen-mips.cc Mon Nov 7
00:41:47 2011
+++ /branches/bleeding_edge/src/mips/full-codegen-mips.cc Mon Nov 7
01:42:54 2011
@@ -1289,30 +1289,62 @@
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.
- }
- context()->Plug(v0);
- }
+ 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(var);
break;
}
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