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236 lines
10 KiB
236 lines
10 KiB
// Copyright (c) 2018 Google LLC.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef SOURCE_OPT_COPY_PROP_ARRAYS_H_
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#define SOURCE_OPT_COPY_PROP_ARRAYS_H_
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#include <memory>
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#include <vector>
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#include "source/opt/mem_pass.h"
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namespace spvtools {
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namespace opt {
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// This pass implements a simple array copy propagation. It does not do a full
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// array data flow. It looks for simple cases that meet the following
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// conditions:
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//
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// 1) The source must never be stored to.
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// 2) The target must be stored to exactly once.
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// 3) The store to the target must be a store to the entire array, and be a
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// copy of the entire source.
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// 4) All loads of the target must be dominated by the store.
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//
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// The hard part is keeping all of the types correct. We do not want to
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// have to do too large a search to update everything, which may not be
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// possible, do we give up if we see any instruction that might be hard to
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// update.
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class CopyPropagateArrays : public MemPass {
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public:
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const char* name() const override { return "copy-propagate-arrays"; }
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Status Process() override;
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IRContext::Analysis GetPreservedAnalyses() override {
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return IRContext::kAnalysisDefUse | IRContext::kAnalysisCFG |
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IRContext::kAnalysisInstrToBlockMapping |
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IRContext::kAnalysisLoopAnalysis | IRContext::kAnalysisDecorations |
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IRContext::kAnalysisDominatorAnalysis | IRContext::kAnalysisNameMap |
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IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
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}
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private:
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// The class used to identify a particular memory object. This memory object
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// will be owned by a particular variable, meaning that the memory is part of
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// that variable. It could be the entire variable or a member of the
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// variable.
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class MemoryObject {
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public:
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// Construction a memory object that is owned by |var_inst|. The iterator
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// |begin| and |end| traverse a container of integers that identify which
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// member of |var_inst| this memory object will represent. These integers
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// are interpreted the same way they would be in an |OpAccessChain|
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// instruction.
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template <class iterator>
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MemoryObject(Instruction* var_inst, iterator begin, iterator end);
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// Change |this| to now point to the member identified by |access_chain|
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// (starting from the current member). The elements in |access_chain| are
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// interpreted the same as the indices in the |OpAccessChain|
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// instruction.
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void GetMember(const std::vector<uint32_t>& access_chain);
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// Change |this| to now represent the first enclosing object to which it
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// belongs. (Remove the last element off the access_chain). It is invalid
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// to call this function if |this| does not represent a member of its owner.
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void GetParent() {
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assert(IsMember());
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access_chain_.pop_back();
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}
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// Returns true if |this| represents a member of its owner, and not the
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// entire variable.
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bool IsMember() const { return !access_chain_.empty(); }
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// Returns the number of members in the object represented by |this|. If
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// |this| does not represent a composite type, the return value will be 0.
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uint32_t GetNumberOfMembers();
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// Returns the owning variable that the memory object is contained in.
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Instruction* GetVariable() const { return variable_inst_; }
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// Returns a vector of integers that can be used to access the specific
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// member that |this| represents starting from the owning variable. These
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// values are to be interpreted the same way the indices are in an
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// |OpAccessChain| instruction.
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const std::vector<uint32_t>& AccessChain() const { return access_chain_; }
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// Returns the type id of the pointer type that can be used to point to this
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// memory object.
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uint32_t GetPointerTypeId(const CopyPropagateArrays* pass) const {
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analysis::DefUseManager* def_use_mgr =
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GetVariable()->context()->get_def_use_mgr();
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analysis::TypeManager* type_mgr =
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GetVariable()->context()->get_type_mgr();
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Instruction* var_pointer_inst =
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def_use_mgr->GetDef(GetVariable()->type_id());
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uint32_t member_type_id = pass->GetMemberTypeId(
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var_pointer_inst->GetSingleWordInOperand(1), GetAccessIds());
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uint32_t member_pointer_type_id = type_mgr->FindPointerToType(
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member_type_id, static_cast<SpvStorageClass>(
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var_pointer_inst->GetSingleWordInOperand(0)));
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return member_pointer_type_id;
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}
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// Returns the storage class of the memory object.
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SpvStorageClass GetStorageClass() const {
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analysis::TypeManager* type_mgr =
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GetVariable()->context()->get_type_mgr();
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const analysis::Pointer* pointer_type =
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type_mgr->GetType(GetVariable()->type_id())->AsPointer();
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return pointer_type->storage_class();
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}
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// Returns true if |other| represents memory that is contains inside of the
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// memory represented by |this|.
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bool Contains(MemoryObject* other);
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private:
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// The variable that owns this memory object.
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Instruction* variable_inst_;
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// The access chain to reach the particular member the memory object
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// represents. It should be interpreted the same way the indices in an
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// |OpAccessChain| are interpreted.
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std::vector<uint32_t> access_chain_;
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std::vector<uint32_t> GetAccessIds() const;
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};
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// Returns the memory object being stored to |var_inst| in the store
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// instruction |store_inst|, if one exists, that can be used in place of
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// |var_inst| in all of the loads of |var_inst|. This code is conservative
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// and only identifies very simple cases. If no such memory object can be
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// found, the return value is |nullptr|.
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std::unique_ptr<CopyPropagateArrays::MemoryObject> FindSourceObjectIfPossible(
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Instruction* var_inst, Instruction* store_inst);
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// Replaces all loads of |var_inst| with a load from |source| instead.
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// |insertion_pos| is a position where it is possible to construct the
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// address of |source| and also dominates all of the loads of |var_inst|.
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void PropagateObject(Instruction* var_inst, MemoryObject* source,
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Instruction* insertion_pos);
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// Returns true if all of the references to |ptr_inst| can be rewritten and
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// are dominated by |store_inst|.
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bool HasValidReferencesOnly(Instruction* ptr_inst, Instruction* store_inst);
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// Returns a memory object that at one time was equivalent to the value in
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// |result|. If no such memory object exists, the return value is |nullptr|.
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std::unique_ptr<MemoryObject> GetSourceObjectIfAny(uint32_t result);
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// Returns the memory object that is loaded by |load_inst|. If a memory
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// object cannot be identified, the return value is |nullptr|. The opcode of
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// |load_inst| must be |OpLoad|.
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std::unique_ptr<MemoryObject> BuildMemoryObjectFromLoad(
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Instruction* load_inst);
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// Returns the memory object that at some point was equivalent to the result
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// of |extract_inst|. If a memory object cannot be identified, the return
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// value is |nullptr|. The opcode of |extract_inst| must be
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// |OpCompositeExtract|.
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std::unique_ptr<MemoryObject> BuildMemoryObjectFromExtract(
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Instruction* extract_inst);
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// Returns the memory object that at some point was equivalent to the result
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// of |construct_inst|. If a memory object cannot be identified, the return
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// value is |nullptr|. The opcode of |constuct_inst| must be
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// |OpCompositeConstruct|.
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std::unique_ptr<MemoryObject> BuildMemoryObjectFromCompositeConstruct(
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Instruction* conststruct_inst);
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// Returns the memory object that at some point was equivalent to the result
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// of |insert_inst|. If a memory object cannot be identified, the return
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// value is |nullptr\. The opcode of |insert_inst| must be
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// |OpCompositeInsert|. This function looks for a series of
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// |OpCompositeInsert| instructions that insert the elements one at a time in
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// order from beginning to end.
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std::unique_ptr<MemoryObject> BuildMemoryObjectFromInsert(
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Instruction* insert_inst);
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// Return true if |type_id| is a pointer type whose pointee type is an array.
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bool IsPointerToArrayType(uint32_t type_id);
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// Returns true of there are not stores using |ptr_inst| or something derived
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// from it.
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bool HasNoStores(Instruction* ptr_inst);
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// Creates an |OpAccessChain| instruction whose result is a pointer the memory
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// represented by |source|. The new instruction will be placed before
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// |insertion_point|. |insertion_point| must be part of a function. Returns
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// the new instruction.
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Instruction* BuildNewAccessChain(Instruction* insertion_point,
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MemoryObject* source) const;
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// Rewrites all uses of |original_ptr| to use |new_pointer_inst| updating
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// types of other instructions as needed. This function should not be called
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// if |CanUpdateUses(original_ptr_inst, new_pointer_inst->type_id())| returns
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// false.
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void UpdateUses(Instruction* original_ptr_inst,
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Instruction* new_pointer_inst);
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// Return true if |UpdateUses| is able to change all of the uses of
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// |original_ptr_inst| to |type_id| and still have valid code.
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bool CanUpdateUses(Instruction* original_ptr_inst, uint32_t type_id);
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// Returns a store to |var_inst| that writes to the entire variable, and is
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// the only store that does so. Note it does not look through OpAccessChain
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// instruction, so partial stores are not considered.
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Instruction* FindStoreInstruction(const Instruction* var_inst) const;
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// Return the type id of the member of the type |id| access using
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// |access_chain|. The elements of |access_chain| are to be interpreted the
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// same way the indexes are used in an |OpCompositeExtract| instruction.
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uint32_t GetMemberTypeId(uint32_t id,
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const std::vector<uint32_t>& access_chain) const;
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};
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} // namespace opt
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} // namespace spvtools
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#endif // SOURCE_OPT_COPY_PROP_ARRAYS_H_
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