Reviewers: Kevin Millikin, Steven,
Description:
Improve Hydrogen code for accessing undefined/null/Infinity.
In some special (but probably very common) cases we can do better than
loading
from a global cell for these global properties by emitting the corresponding
constant directly. This opens up opportunities for further improvements,
coming
in a separate CL...
Please review this at http://codereview.chromium.org/7992002/
SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/
Affected files:
M src/factory.h
M src/factory.cc
M src/heap.h
M src/heap.cc
M src/hydrogen.cc
Index: src/factory.cc
===================================================================
--- src/factory.cc (revision 9392)
+++ src/factory.cc (working copy)
@@ -1315,4 +1315,13 @@
}
+Handle<Object> Factory::GlobalConstantFor(Handle<String> name) {
+ Heap* h = isolate()->heap();
+ if (name->Equals(h->undefined_symbol())) return undefined_value();
+ if (name->Equals(h->nan_symbol())) return nan_value();
+ if (name->Equals(h->infinity_symbol())) return infinity_value();
+ return Handle<Object>::null();
+}
+
+
} } // namespace v8::internal
Index: src/factory.h
===================================================================
--- src/factory.h (revision 9392)
+++ src/factory.h (working copy)
@@ -444,6 +444,10 @@
JSRegExp::Flags flags,
int capture_count);
+ // Returns the value for a known global constant like 'undefined' or
+ // a null handle when the given name is unknown.
+ Handle<Object> GlobalConstantFor(Handle<String> name);
+
private:
Isolate* isolate() { return reinterpret_cast<Isolate*>(this); }
Index: src/heap.cc
===================================================================
--- src/heap.cc (revision 9392)
+++ src/heap.cc (working copy)
@@ -2192,6 +2192,11 @@
}
set_nan_value(obj);
+ { MaybeObject* maybe_obj = AllocateHeapNumber(V8_INFINITY, TENURED);
+ if (!maybe_obj->ToObject(&obj)) return false;
+ }
+ set_infinity_value(obj);
+
{ MaybeObject* maybe_obj = Allocate(oddball_map(), OLD_POINTER_SPACE);
if (!maybe_obj->ToObject(&obj)) return false;
}
Index: src/heap.h
===================================================================
--- src/heap.h (revision 9392)
+++ src/heap.h (working copy)
@@ -126,6 +126,7 @@
V(Map, message_object_map,
JSMessageObjectMap) \
V(Map, foreign_map,
ForeignMap) \
V(Object, nan_value,
NanValue) \
+ V(Object, infinity_value,
InfinityValue) \
V(Object, minus_zero_value,
MinusZeroValue) \
V(Map, neander_map,
NeanderMap) \
V(JSObject, message_listeners,
MessageListeners) \
@@ -229,7 +230,8 @@
V(closure_symbol, "(closure)") \
V(use_strict, "use strict") \
V(dot_symbol, ".") \
- V(anonymous_function_symbol, "(anonymous function)")
+ V(anonymous_function_symbol, "(anonymous function)") \
+ V(infinity_symbol, "Infinity")
// Forward declarations.
class GCTracer;
Index: src/hydrogen.cc
===================================================================
--- src/hydrogen.cc (revision 9392)
+++ src/hydrogen.cc (working copy)
@@ -3146,6 +3146,16 @@
}
switch (variable->location()) {
case Variable::UNALLOCATED: {
+ // Handle known global constants like 'undefined' specially to avoid
a
+ // load from a global cell for them.
+ Handle<Object> constant_value =
+ isolate()->factory()->GlobalConstantFor(variable->name());
+ if (!constant_value.is_null()) {
+ HConstant* instr =
+ new(zone()) HConstant(constant_value,
Representation::Tagged());
+ return ast_context()->ReturnInstruction(instr, expr->id());
+ }
+
LookupResult lookup;
GlobalPropertyAccess type =
LookupGlobalProperty(variable, &lookup, false);
--
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