Reviewers: Yang,
Description:
Eliminate a superfluous map check when building generic array element
access.
In the case where we generate a generic load or store, we don't need to
emit a
non-smi-check and a map-check before it.
Please review this at http://codereview.chromium.org/9252008/
SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/
Affected files:
M src/hydrogen.cc
M src/objects.h
Index: src/hydrogen.cc
===================================================================
--- src/hydrogen.cc (revision 10428)
+++ src/hydrogen.cc (working copy)
@@ -4266,14 +4266,6 @@
HInstruction* mapcheck = AddInstruction(new(zone()) HCheckMap(object,
map));
bool fast_smi_only_elements = map->has_fast_smi_only_elements();
bool fast_elements = map->has_fast_elements();
- bool fast_double_elements = map->has_fast_double_elements();
- if (!fast_smi_only_elements &&
- !fast_elements &&
- !fast_double_elements &&
- !map->has_external_array_elements()) {
- return is_store ? BuildStoreKeyedGeneric(object, key, val)
- : BuildLoadKeyedGeneric(object, key);
- }
HInstruction* elements = AddInstruction(new(zone())
HLoadElements(object));
if (is_store && (fast_elements || fast_smi_only_elements)) {
AddInstruction(new(zone()) HCheckMap(
@@ -4290,7 +4282,9 @@
return BuildExternalArrayElementAccess(external_elements, checked_key,
val, map->elements_kind(),
is_store);
}
- ASSERT(fast_smi_only_elements || fast_elements || fast_double_elements);
+ ASSERT(fast_smi_only_elements ||
+ fast_elements ||
+ map->has_fast_double_elements());
if (map->instance_type() == JS_ARRAY_TYPE) {
length = AddInstruction(new(zone()) HJSArrayLength(object, mapcheck));
} else {
@@ -4362,8 +4356,14 @@
// If only one map is left after transitioning, handle this case
// monomorphically.
if (num_untransitionable_maps == 1) {
- HInstruction* instr = AddInstruction(BuildMonomorphicElementAccess(
- object, key, val, untransitionable_map, is_store));
+ HInstruction* instr = NULL;
+ if (untransitionable_map->has_slow_elements_kind()) {
+ instr = AddInstruction(is_store ? BuildStoreKeyedGeneric(object,
key, val)
+ : BuildLoadKeyedGeneric(object,
key));
+ } else {
+ instr = AddInstruction(BuildMonomorphicElementAccess(
+ object, key, val, untransitionable_map, is_store));
+ }
*has_side_effects |= instr->HasObservableSideEffects();
instr->set_position(position);
return is_store ? NULL : instr;
@@ -4499,8 +4499,13 @@
HInstruction* instr = NULL;
if (expr->IsMonomorphic()) {
Handle<Map> map = expr->GetMonomorphicReceiverType();
- AddInstruction(new(zone()) HCheckNonSmi(obj));
- instr = BuildMonomorphicElementAccess(obj, key, val, map, is_store);
+ if (map->has_slow_elements_kind()) {
+ instr = is_store ? BuildStoreKeyedGeneric(obj, key, val)
+ : BuildLoadKeyedGeneric(obj, key);
+ } else {
+ AddInstruction(new(zone()) HCheckNonSmi(obj));
+ instr = BuildMonomorphicElementAccess(obj, key, val, map, is_store);
+ }
} else if (expr->GetReceiverTypes() != NULL &&
!expr->GetReceiverTypes()->is_empty()) {
return HandlePolymorphicElementAccess(
Index: src/objects.h
===================================================================
--- src/objects.h (revision 10428)
+++ src/objects.h (working copy)
@@ -4492,6 +4492,11 @@
return elements_kind() == DICTIONARY_ELEMENTS;
}
+ inline bool has_slow_elements_kind() {
+ return elements_kind() == DICTIONARY_ELEMENTS
+ || elements_kind() == NON_STRICT_ARGUMENTS_ELEMENTS;
+ }
+
static bool IsValidElementsTransition(ElementsKind from_kind,
ElementsKind to_kind);
--
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