--- /dev/null
+// Copyright 2013 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following
+// disclaimer in the documentation and/or other materials provided
+// with the distribution.
+// * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived
+// from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "hydrogen-check-elimination.h"
+#include "hydrogen-alias-analysis.h"
+
+namespace v8 {
+namespace internal {
+
+static const int kMaxTrackedObjects = 10;
+typedef UniqueSet<Map>* MapSet;
+
+// The main datastructure used during check elimination, which stores a
+// set of known maps for each object.
+class HCheckTable {
+ public:
+ explicit HCheckTable(Zone* zone) : zone_(zone) {
+ Kill();
+ redundant_ = 0;
+ narrowed_ = 0;
+ empty_ = 0;
+ removed_ = 0;
+ compares_true_ = 0;
+ compares_false_ = 0;
+ transitions_ = 0;
+ loads_ = 0;
+ }
+
+ void ReduceCheckMaps(HCheckMaps* instr) {
+ HValue* object = instr->value()->ActualValue();
+ int index = Find(object);
+ if (index >= 0) {
+ // entry found;
+ MapSet a = known_maps_[index];
+ MapSet i = instr->map_set().Copy(zone_);
+ if (a->IsSubset(i)) {
+ // The first check is more strict; the second is redundant.
+ if (checks_[index] != NULL) {
+ instr->DeleteAndReplaceWith(checks_[index]);
+ redundant_++;
+ } else {
+ instr->DeleteAndReplaceWith(instr->value());
+ removed_++;
+ }
+ return;
+ }
+ i = i->Intersect(a, zone_);
+ if (i->size() == 0) {
+ // Intersection is empty; probably megamorphic, which is likely to
+ // deopt anyway, so just leave things as they are.
+ empty_++;
+ } else {
+ // TODO(titzer): replace the first check with a more strict check.
+ narrowed_++;
+ }
+ } else {
+ // No entry; insert a new one.
+ Insert(object, instr, instr->map_set().Copy(zone_));
+ }
+ }
+
+ void ReduceCheckValue(HCheckValue* instr) {
+ // Canonicalize HCheckValues; they might have their values load-eliminated.
+ HValue* value = instr->Canonicalize();
+ if (value == NULL) {
+ instr->DeleteAndReplaceWith(instr->value());
+ removed_++;
+ } else if (value != instr) {
+ instr->DeleteAndReplaceWith(value);
+ redundant_++;
+ }
+ }
+
+ void ReduceLoadNamedField(HLoadNamedField* instr) {
+ // Reduce a load of the map field when it is known to be a constant.
+ if (!IsMapAccess(instr->access())) return;
+
+ HValue* object = instr->object()->ActualValue();
+ MapSet maps = FindMaps(object);
+ if (maps == NULL || maps->size() != 1) return; // Not a constant.
+
+ Unique<Map> map = maps->at(0);
+ HConstant* constant = HConstant::CreateAndInsertBefore(
+ instr->block()->graph()->zone(), map, true, instr);
+ instr->DeleteAndReplaceWith(constant);
+ loads_++;
+ }
+
+ void ReduceCheckMapValue(HCheckMapValue* instr) {
+ if (!instr->map()->IsConstant()) return; // Nothing to learn.
+
+ HValue* object = instr->value()->ActualValue();
+ // Match a HCheckMapValue(object, HConstant(map))
+ Unique<Map> map = MapConstant(instr->map());
+ MapSet maps = FindMaps(object);
+ if (maps != NULL) {
+ if (maps->Contains(map)) {
+ if (maps->size() == 1) {
+ // Object is known to have exactly this map.
+ instr->DeleteAndReplaceWith(NULL);
+ removed_++;
+ } else {
+ // Only one map survives the check.
+ maps->Clear();
+ maps->Add(map, zone_);
+ }
+ }
+ } else {
+ // No prior information.
+ Insert(object, map);
+ }
+ }
+
+ void ReduceStoreNamedField(HStoreNamedField* instr) {
+ HValue* object = instr->object()->ActualValue();
+ if (instr->has_transition()) {
+ // This store transitions the object to a new map.
+ Kill(object);
+ Insert(object, MapConstant(instr->transition()));
+ } else if (IsMapAccess(instr->access())) {
+ // This is a store directly to the map field of the object.
+ Kill(object);
+ if (!instr->value()->IsConstant()) return;
+ Insert(object, MapConstant(instr->value()));
+ } else if (instr->CheckGVNFlag(kChangesMaps)) {
+ // This store indirectly changes the map of the object.
+ Kill(instr->object());
+ UNREACHABLE();
+ }
+ }
+
+ void ReduceCompareMap(HCompareMap* instr) {
+ MapSet maps = FindMaps(instr->value()->ActualValue());
+ if (maps == NULL) return;
+ if (maps->Contains(instr->map())) {
+ // TODO(titzer): replace with goto true branch
+ if (maps->size() == 1) compares_true_++;
+ } else {
+ // TODO(titzer): replace with goto false branch
+ compares_false_++;
+ }
+ }
+
+ void ReduceTransitionElementsKind(HTransitionElementsKind* instr) {
+ MapSet maps = FindMaps(instr->object()->ActualValue());
+ // Can only learn more about an object that already has a known set of maps.
+ if (maps == NULL) return;
+ if (maps->Contains(instr->original_map())) {
+ // If the object has the original map, it will be transitioned.
+ maps->Remove(instr->original_map());
+ maps->Add(instr->transitioned_map(), zone_);
+ } else {
+ // Object does not have the given map, thus the transition is redundant.
+ instr->DeleteAndReplaceWith(instr->object());
+ transitions_++;
+ }
+ }
+
+ // Kill everything in the table.
+ void Kill() {
+ memset(objects_, 0, sizeof(objects_));
+ }
+
+ // Kill everything in the table that may alias {object}.
+ void Kill(HValue* object) {
+ for (int i = 0; i < kMaxTrackedObjects; i++) {
+ if (objects_[i] == NULL) continue;
+ if (aliasing_.MayAlias(objects_[i], object)) objects_[i] = NULL;
+ }
+ ASSERT(Find(object) < 0);
+ }
+
+ void Print() {
+ for (int i = 0; i < kMaxTrackedObjects; i++) {
+ if (objects_[i] == NULL) continue;
+ PrintF(" checkmaps-table @%d: object #%d ", i, objects_[i]->id());
+ if (checks_[i] != NULL) {
+ PrintF("check #%d ", checks_[i]->id());
+ }
+ MapSet list = known_maps_[i];
+ PrintF("%d maps { ", list->size());
+ for (int j = 0; j < list->size(); j++) {
+ if (j > 0) PrintF(", ");
+ PrintF("%" V8PRIxPTR, list->at(j).Hashcode());
+ }
+ PrintF(" }\n");
+ }
+ }
+
+ void PrintStats() {
+ if (redundant_ > 0) PrintF(" redundant = %2d\n", redundant_);
+ if (removed_ > 0) PrintF(" removed = %2d\n", removed_);
+ if (narrowed_ > 0) PrintF(" narrowed = %2d\n", narrowed_);
+ if (loads_ > 0) PrintF(" loads = %2d\n", loads_);
+ if (empty_ > 0) PrintF(" empty = %2d\n", empty_);
+ if (compares_true_ > 0) PrintF(" cmp_true = %2d\n", compares_true_);
+ if (compares_false_ > 0) PrintF(" cmp_false = %2d\n", compares_false_);
+ if (transitions_ > 0) PrintF(" transitions = %2d\n", transitions_);
+ }
+
+ private:
+ int Find(HValue* object) {
+ for (int i = 0; i < kMaxTrackedObjects; i++) {
+ if (objects_[i] == NULL) continue;
+ if (aliasing_.MustAlias(objects_[i], object)) return i;
+ }
+ return -1;
+ }
+
+ MapSet FindMaps(HValue* object) {
+ int index = Find(object);
+ return index < 0 ? NULL : known_maps_[index];
+ }
+
+ void Insert(HValue* object, Unique<Map> map) {
+ MapSet list = new(zone_) UniqueSet<Map>();
+ list->Add(map, zone_);
+ Insert(object, NULL, list);
+ }
+
+ void Insert(HValue* object, HCheckMaps* check, MapSet maps) {
+ for (int i = 0; i < kMaxTrackedObjects; i++) {
+ // TODO(titzer): drop old entries instead of disallowing new ones.
+ if (objects_[i] == NULL) {
+ objects_[i] = object;
+ checks_[i] = check;
+ known_maps_[i] = maps;
+ return;
+ }
+ }
+ }
+
+ bool IsMapAccess(HObjectAccess access) {
+ return access.IsInobject() && access.offset() == JSObject::kMapOffset;
+ }
+
+ Unique<Map> MapConstant(HValue* value) {
+ return Unique<Map>::cast(HConstant::cast(value)->GetUnique());
+ }
+
+ Zone* zone_;
+ HValue* objects_[kMaxTrackedObjects];
+ HValue* checks_[kMaxTrackedObjects];
+ MapSet known_maps_[kMaxTrackedObjects];
+ HAliasAnalyzer aliasing_;
+ int redundant_;
+ int removed_;
+ int narrowed_;
+ int loads_;
+ int empty_;
+ int compares_true_;
+ int compares_false_;
+ int transitions_;
+};
+
+
+void HCheckEliminationPhase::Run() {
+ for (int i = 0; i < graph()->blocks()->length(); i++) {
+ EliminateLocalChecks(graph()->blocks()->at(i));
+ }
+}
+
+
+// For code de-uglification.
+#define TRACE(x) if (FLAG_trace_check_elimination) PrintF x
+
+
+// Eliminate checks local to a block.
+void HCheckEliminationPhase::EliminateLocalChecks(HBasicBlock* block) {
+ HCheckTable table(zone());
+ TRACE(("-- check-elim B%d ------------------------------------------------\n",
+ block->block_id()));
+
+ for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
+ bool changed = false;
+ HInstruction* instr = it.Current();
+
+ switch (instr->opcode()) {
+ case HValue::kCheckMaps: {
+ table.ReduceCheckMaps(HCheckMaps::cast(instr));
+ changed = true;
+ break;
+ }
+ case HValue::kCheckValue: {
+ table.ReduceCheckValue(HCheckValue::cast(instr));
+ changed = true;
+ break;
+ }
+ case HValue::kLoadNamedField: {
+ table.ReduceLoadNamedField(HLoadNamedField::cast(instr));
+ changed = true;
+ break;
+ }
+ case HValue::kStoreNamedField: {
+ table.ReduceStoreNamedField(HStoreNamedField::cast(instr));
+ changed = true;
+ break;
+ }
+ case HValue::kCompareMap: {
+ table.ReduceCompareMap(HCompareMap::cast(instr));
+ changed = true;
+ break;
+ }
+ case HValue::kTransitionElementsKind: {
+ table.ReduceTransitionElementsKind(
+ HTransitionElementsKind::cast(instr));
+ changed = true;
+ break;
+ }
+ case HValue::kCheckMapValue: {
+ table.ReduceCheckMapValue(HCheckMapValue::cast(instr));
+ changed = true;
+ break;
+ }
+ default: {
+ // If the instruction changes maps uncontrollably, kill the whole town.
+ if (instr->CheckGVNFlag(kChangesMaps)) {
+ table.Kill();
+ changed = true;
+ }
+ }
+ // Improvements possible:
+ // - eliminate HCheckSmi and HCheckHeapObject
+ }
+
+ if (changed && FLAG_trace_check_elimination) table.Print();
+ }
+
+ if (FLAG_trace_check_elimination) table.PrintStats();
+}
+
+
+} } // namespace v8::internal
--- /dev/null
+// Copyright 2013 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following
+// disclaimer in the documentation and/or other materials provided
+// with the distribution.
+// * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived
+// from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_HYDROGEN_CHECK_ELIMINATION_H_
+#define V8_HYDROGEN_CHECK_ELIMINATION_H_
+
+#include "hydrogen.h"
+
+namespace v8 {
+namespace internal {
+
+
+// Remove CheckMaps instructions through flow- and branch-sensitive analysis.
+class HCheckEliminationPhase : public HPhase {
+ public:
+ explicit HCheckEliminationPhase(HGraph* graph)
+ : HPhase("H_Check Elimination", graph) { }
+
+ void Run();
+
+ private:
+ void EliminateLocalChecks(HBasicBlock* block);
+};
+
+
+} } // namespace v8::internal
+
+#endif // V8_HYDROGEN_CHECK_ELIMINATION_H_
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