| // 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-bce.h" |
| |
| namespace v8 { |
| namespace internal { |
| |
| // We try to "factor up" HBoundsCheck instructions towards the root of the |
| // dominator tree. |
| // For now we handle checks where the index is like "exp + int32value". |
| // If in the dominator tree we check "exp + v1" and later (dominated) |
| // "exp + v2", if v2 <= v1 we can safely remove the second check, and if |
| // v2 > v1 we can use v2 in the 1st check and again remove the second. |
| // To do so we keep a dictionary of all checks where the key if the pair |
| // "exp, length". |
| // The class BoundsCheckKey represents this key. |
| class BoundsCheckKey : public ZoneObject { |
| public: |
| HValue* IndexBase() const { return index_base_; } |
| HValue* Length() const { return length_; } |
| |
| uint32_t Hash() { |
| return static_cast<uint32_t>(index_base_->Hashcode() ^ length_->Hashcode()); |
| } |
| |
| static BoundsCheckKey* Create(Zone* zone, |
| HBoundsCheck* check, |
| int32_t* offset) { |
| if (!check->index()->representation().IsSmiOrInteger32()) return NULL; |
| |
| HValue* index_base = NULL; |
| HConstant* constant = NULL; |
| bool is_sub = false; |
| |
| if (check->index()->IsAdd()) { |
| HAdd* index = HAdd::cast(check->index()); |
| if (index->left()->IsConstant()) { |
| constant = HConstant::cast(index->left()); |
| index_base = index->right(); |
| } else if (index->right()->IsConstant()) { |
| constant = HConstant::cast(index->right()); |
| index_base = index->left(); |
| } |
| } else if (check->index()->IsSub()) { |
| HSub* index = HSub::cast(check->index()); |
| is_sub = true; |
| if (index->left()->IsConstant()) { |
| constant = HConstant::cast(index->left()); |
| index_base = index->right(); |
| } else if (index->right()->IsConstant()) { |
| constant = HConstant::cast(index->right()); |
| index_base = index->left(); |
| } |
| } |
| |
| if (constant != NULL && constant->HasInteger32Value()) { |
| *offset = is_sub ? - constant->Integer32Value() |
| : constant->Integer32Value(); |
| } else { |
| *offset = 0; |
| index_base = check->index(); |
| } |
| |
| return new(zone) BoundsCheckKey(index_base, check->length()); |
| } |
| |
| private: |
| BoundsCheckKey(HValue* index_base, HValue* length) |
| : index_base_(index_base), |
| length_(length) { } |
| |
| HValue* index_base_; |
| HValue* length_; |
| |
| DISALLOW_COPY_AND_ASSIGN(BoundsCheckKey); |
| }; |
| |
| |
| // Data about each HBoundsCheck that can be eliminated or moved. |
| // It is the "value" in the dictionary indexed by "base-index, length" |
| // (the key is BoundsCheckKey). |
| // We scan the code with a dominator tree traversal. |
| // Traversing the dominator tree we keep a stack (implemented as a singly |
| // linked list) of "data" for each basic block that contains a relevant check |
| // with the same key (the dictionary holds the head of the list). |
| // We also keep all the "data" created for a given basic block in a list, and |
| // use it to "clean up" the dictionary when backtracking in the dominator tree |
| // traversal. |
| // Doing this each dictionary entry always directly points to the check that |
| // is dominating the code being examined now. |
| // We also track the current "offset" of the index expression and use it to |
| // decide if any check is already "covered" (so it can be removed) or not. |
| class BoundsCheckBbData: public ZoneObject { |
| public: |
| BoundsCheckKey* Key() const { return key_; } |
| int32_t LowerOffset() const { return lower_offset_; } |
| int32_t UpperOffset() const { return upper_offset_; } |
| HBasicBlock* BasicBlock() const { return basic_block_; } |
| HBoundsCheck* LowerCheck() const { return lower_check_; } |
| HBoundsCheck* UpperCheck() const { return upper_check_; } |
| BoundsCheckBbData* NextInBasicBlock() const { return next_in_bb_; } |
| BoundsCheckBbData* FatherInDominatorTree() const { return father_in_dt_; } |
| |
| bool OffsetIsCovered(int32_t offset) const { |
| return offset >= LowerOffset() && offset <= UpperOffset(); |
| } |
| |
| bool HasSingleCheck() { return lower_check_ == upper_check_; } |
| |
| // The goal of this method is to modify either upper_offset_ or |
| // lower_offset_ so that also new_offset is covered (the covered |
| // range grows). |
| // |
| // The precondition is that new_check follows UpperCheck() and |
| // LowerCheck() in the same basic block, and that new_offset is not |
| // covered (otherwise we could simply remove new_check). |
| // |
| // If HasSingleCheck() is true then new_check is added as "second check" |
| // (either upper or lower; note that HasSingleCheck() becomes false). |
| // Otherwise one of the current checks is modified so that it also covers |
| // new_offset, and new_check is removed. |
| // |
| // If the check cannot be modified because the context is unknown it |
| // returns false, otherwise it returns true. |
| bool CoverCheck(HBoundsCheck* new_check, |
| int32_t new_offset) { |
| ASSERT(new_check->index()->representation().IsSmiOrInteger32()); |
| bool keep_new_check = false; |
| |
| if (new_offset > upper_offset_) { |
| upper_offset_ = new_offset; |
| if (HasSingleCheck()) { |
| keep_new_check = true; |
| upper_check_ = new_check; |
| } else { |
| bool result = BuildOffsetAdd(upper_check_, |
| &added_upper_index_, |
| &added_upper_offset_, |
| Key()->IndexBase(), |
| new_check->index()->representation(), |
| new_offset); |
| if (!result) return false; |
| upper_check_->ReplaceAllUsesWith(upper_check_->index()); |
| upper_check_->SetOperandAt(0, added_upper_index_); |
| } |
| } else if (new_offset < lower_offset_) { |
| lower_offset_ = new_offset; |
| if (HasSingleCheck()) { |
| keep_new_check = true; |
| lower_check_ = new_check; |
| } else { |
| bool result = BuildOffsetAdd(lower_check_, |
| &added_lower_index_, |
| &added_lower_offset_, |
| Key()->IndexBase(), |
| new_check->index()->representation(), |
| new_offset); |
| if (!result) return false; |
| lower_check_->ReplaceAllUsesWith(lower_check_->index()); |
| lower_check_->SetOperandAt(0, added_lower_index_); |
| } |
| } else { |
| ASSERT(false); |
| } |
| |
| if (!keep_new_check) { |
| new_check->block()->graph()->isolate()->counters()-> |
| bounds_checks_eliminated()->Increment(); |
| new_check->DeleteAndReplaceWith(new_check->ActualValue()); |
| } |
| |
| return true; |
| } |
| |
| void RemoveZeroOperations() { |
| RemoveZeroAdd(&added_lower_index_, &added_lower_offset_); |
| RemoveZeroAdd(&added_upper_index_, &added_upper_offset_); |
| } |
| |
| BoundsCheckBbData(BoundsCheckKey* key, |
| int32_t lower_offset, |
| int32_t upper_offset, |
| HBasicBlock* bb, |
| HBoundsCheck* lower_check, |
| HBoundsCheck* upper_check, |
| BoundsCheckBbData* next_in_bb, |
| BoundsCheckBbData* father_in_dt) |
| : key_(key), |
| lower_offset_(lower_offset), |
| upper_offset_(upper_offset), |
| basic_block_(bb), |
| lower_check_(lower_check), |
| upper_check_(upper_check), |
| added_lower_index_(NULL), |
| added_lower_offset_(NULL), |
| added_upper_index_(NULL), |
| added_upper_offset_(NULL), |
| next_in_bb_(next_in_bb), |
| father_in_dt_(father_in_dt) { } |
| |
| private: |
| BoundsCheckKey* key_; |
| int32_t lower_offset_; |
| int32_t upper_offset_; |
| HBasicBlock* basic_block_; |
| HBoundsCheck* lower_check_; |
| HBoundsCheck* upper_check_; |
| HInstruction* added_lower_index_; |
| HConstant* added_lower_offset_; |
| HInstruction* added_upper_index_; |
| HConstant* added_upper_offset_; |
| BoundsCheckBbData* next_in_bb_; |
| BoundsCheckBbData* father_in_dt_; |
| |
| // Given an existing add instruction and a bounds check it tries to |
| // find the current context (either of the add or of the check index). |
| HValue* IndexContext(HInstruction* add, HBoundsCheck* check) { |
| if (add != NULL && add->IsAdd()) { |
| return HAdd::cast(add)->context(); |
| } |
| if (check->index()->IsBinaryOperation()) { |
| return HBinaryOperation::cast(check->index())->context(); |
| } |
| return NULL; |
| } |
| |
| // This function returns false if it cannot build the add because the |
| // current context cannot be determined. |
| bool BuildOffsetAdd(HBoundsCheck* check, |
| HInstruction** add, |
| HConstant** constant, |
| HValue* original_value, |
| Representation representation, |
| int32_t new_offset) { |
| HValue* index_context = IndexContext(*add, check); |
| if (index_context == NULL) return false; |
| |
| Zone* zone = BasicBlock()->zone(); |
| HConstant* new_constant = HConstant::New(zone, index_context, |
| new_offset, representation); |
| if (*add == NULL) { |
| new_constant->InsertBefore(check); |
| (*add) = HAdd::New(zone, index_context, original_value, new_constant); |
| (*add)->AssumeRepresentation(representation); |
| (*add)->InsertBefore(check); |
| } else { |
| new_constant->InsertBefore(*add); |
| (*constant)->DeleteAndReplaceWith(new_constant); |
| } |
| *constant = new_constant; |
| return true; |
| } |
| |
| void RemoveZeroAdd(HInstruction** add, HConstant** constant) { |
| if (*add != NULL && (*add)->IsAdd() && (*constant)->Integer32Value() == 0) { |
| (*add)->DeleteAndReplaceWith(HAdd::cast(*add)->left()); |
| (*constant)->DeleteAndReplaceWith(NULL); |
| } |
| } |
| |
| DISALLOW_COPY_AND_ASSIGN(BoundsCheckBbData); |
| }; |
| |
| |
| static bool BoundsCheckKeyMatch(void* key1, void* key2) { |
| BoundsCheckKey* k1 = static_cast<BoundsCheckKey*>(key1); |
| BoundsCheckKey* k2 = static_cast<BoundsCheckKey*>(key2); |
| return k1->IndexBase() == k2->IndexBase() && k1->Length() == k2->Length(); |
| } |
| |
| |
| BoundsCheckTable::BoundsCheckTable(Zone* zone) |
| : ZoneHashMap(BoundsCheckKeyMatch, ZoneHashMap::kDefaultHashMapCapacity, |
| ZoneAllocationPolicy(zone)) { } |
| |
| |
| BoundsCheckBbData** BoundsCheckTable::LookupOrInsert(BoundsCheckKey* key, |
| Zone* zone) { |
| return reinterpret_cast<BoundsCheckBbData**>( |
| &(Lookup(key, key->Hash(), true, ZoneAllocationPolicy(zone))->value)); |
| } |
| |
| |
| void BoundsCheckTable::Insert(BoundsCheckKey* key, |
| BoundsCheckBbData* data, |
| Zone* zone) { |
| Lookup(key, key->Hash(), true, ZoneAllocationPolicy(zone))->value = data; |
| } |
| |
| |
| void BoundsCheckTable::Delete(BoundsCheckKey* key) { |
| Remove(key, key->Hash()); |
| } |
| |
| |
| class HBoundsCheckEliminationState { |
| public: |
| HBasicBlock* block_; |
| BoundsCheckBbData* bb_data_list_; |
| int index_; |
| }; |
| |
| |
| // Eliminates checks in bb and recursively in the dominated blocks. |
| // Also replace the results of check instructions with the original value, if |
| // the result is used. This is safe now, since we don't do code motion after |
| // this point. It enables better register allocation since the value produced |
| // by check instructions is really a copy of the original value. |
| void HBoundsCheckEliminationPhase::EliminateRedundantBoundsChecks( |
| HBasicBlock* entry) { |
| // Allocate the stack. |
| HBoundsCheckEliminationState* stack = |
| zone()->NewArray<HBoundsCheckEliminationState>(graph()->blocks()->length()); |
| |
| // Explicitly push the entry block. |
| stack[0].block_ = entry; |
| stack[0].bb_data_list_ = PreProcessBlock(entry); |
| stack[0].index_ = 0; |
| int stack_depth = 1; |
| |
| // Implement depth-first traversal with a stack. |
| while (stack_depth > 0) { |
| int current = stack_depth - 1; |
| HBoundsCheckEliminationState* state = &stack[current]; |
| const ZoneList<HBasicBlock*>* children = state->block_->dominated_blocks(); |
| |
| if (state->index_ < children->length()) { |
| // Recursively visit children blocks. |
| HBasicBlock* child = children->at(state->index_++); |
| int next = stack_depth++; |
| stack[next].block_ = child; |
| stack[next].bb_data_list_ = PreProcessBlock(child); |
| stack[next].index_ = 0; |
| } else { |
| // Finished with all children; post process the block. |
| PostProcessBlock(state->block_, state->bb_data_list_); |
| stack_depth--; |
| } |
| } |
| } |
| |
| |
| BoundsCheckBbData* HBoundsCheckEliminationPhase::PreProcessBlock( |
| HBasicBlock* bb) { |
| BoundsCheckBbData* bb_data_list = NULL; |
| |
| for (HInstructionIterator it(bb); !it.Done(); it.Advance()) { |
| HInstruction* i = it.Current(); |
| if (!i->IsBoundsCheck()) continue; |
| |
| HBoundsCheck* check = HBoundsCheck::cast(i); |
| int32_t offset; |
| BoundsCheckKey* key = |
| BoundsCheckKey::Create(zone(), check, &offset); |
| if (key == NULL) continue; |
| BoundsCheckBbData** data_p = table_.LookupOrInsert(key, zone()); |
| BoundsCheckBbData* data = *data_p; |
| if (data == NULL) { |
| bb_data_list = new(zone()) BoundsCheckBbData(key, |
| offset, |
| offset, |
| bb, |
| check, |
| check, |
| bb_data_list, |
| NULL); |
| *data_p = bb_data_list; |
| } else if (data->OffsetIsCovered(offset)) { |
| bb->graph()->isolate()->counters()-> |
| bounds_checks_eliminated()->Increment(); |
| check->DeleteAndReplaceWith(check->ActualValue()); |
| } else if (data->BasicBlock() != bb || |
| !data->CoverCheck(check, offset)) { |
| // If the check is in the current BB we try to modify it by calling |
| // "CoverCheck", but if also that fails we record the current offsets |
| // in a new data instance because from now on they are covered. |
| int32_t new_lower_offset = offset < data->LowerOffset() |
| ? offset |
| : data->LowerOffset(); |
| int32_t new_upper_offset = offset > data->UpperOffset() |
| ? offset |
| : data->UpperOffset(); |
| bb_data_list = new(zone()) BoundsCheckBbData(key, |
| new_lower_offset, |
| new_upper_offset, |
| bb, |
| data->LowerCheck(), |
| data->UpperCheck(), |
| bb_data_list, |
| data); |
| table_.Insert(key, bb_data_list, zone()); |
| } |
| } |
| |
| return bb_data_list; |
| } |
| |
| |
| void HBoundsCheckEliminationPhase::PostProcessBlock( |
| HBasicBlock* block, BoundsCheckBbData* data) { |
| while (data != NULL) { |
| data->RemoveZeroOperations(); |
| if (data->FatherInDominatorTree()) { |
| table_.Insert(data->Key(), data->FatherInDominatorTree(), zone()); |
| } else { |
| table_.Delete(data->Key()); |
| } |
| data = data->NextInBasicBlock(); |
| } |
| } |
| |
| } } // namespace v8::internal |
