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// Copyright (c) 2018 Google LLC.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include <memory>
#include <vector>
#include "source/opt/mem_pass.h"
namespace spvtools {
namespace opt {
// This pass implements a simple array copy propagation. It does not do a full
// array data flow. It looks for simple cases that meet the following
// conditions:
// 1) The source must never be stored to.
// 2) The target must be stored to exactly once.
// 3) The store to the target must be a store to the entire array, and be a
// copy of the entire source.
// 4) All loads of the target must be dominated by the store.
// The hard part is keeping all of the types correct. We do not want to
// have to do too large a search to update everything, which may not be
// possible, do we give up if we see any instruction that might be hard to
// update.
class CopyPropagateArrays : public MemPass {
const char* name() const override { return "copy-propagate-arrays"; }
Status Process() override;
IRContext::Analysis GetPreservedAnalyses() override {
return IRContext::kAnalysisDefUse | IRContext::kAnalysisCFG |
IRContext::kAnalysisInstrToBlockMapping |
IRContext::kAnalysisLoopAnalysis | IRContext::kAnalysisDecorations |
IRContext::kAnalysisDominatorAnalysis | IRContext::kAnalysisNameMap |
IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
// The class used to identify a particular memory object. This memory object
// will be owned by a particular variable, meaning that the memory is part of
// that variable. It could be the entire variable or a member of the
// variable.
class MemoryObject {
// Construction a memory object that is owned by |var_inst|. The iterator
// |begin| and |end| traverse a container of integers that identify which
// member of |var_inst| this memory object will represent. These integers
// are interpreted the same way they would be in an |OpAccessChain|
// instruction.
template <class iterator>
MemoryObject(Instruction* var_inst, iterator begin, iterator end);
// Change |this| to now point to the member identified by |access_chain|
// (starting from the current member). The elements in |access_chain| are
// interpreted the same as the indices in the |OpAccessChain|
// instruction.
void GetMember(const std::vector<uint32_t>& access_chain);
// Change |this| to now represent the first enclosing object to which it
// belongs. (Remove the last element off the access_chain). It is invalid
// to call this function if |this| does not represent a member of its owner.
void GetParent() {
// Returns true if |this| represents a member of its owner, and not the
// entire variable.
bool IsMember() const { return !access_chain_.empty(); }
// Returns the number of members in the object represented by |this|. If
// |this| does not represent a composite type, the return value will be 0.
uint32_t GetNumberOfMembers();
// Returns the owning variable that the memory object is contained in.
Instruction* GetVariable() const { return variable_inst_; }
// Returns a vector of integers that can be used to access the specific
// member that |this| represents starting from the owning variable. These
// values are to be interpreted the same way the indices are in an
// |OpAccessChain| instruction.
const std::vector<uint32_t>& AccessChain() const { return access_chain_; }
// Returns the type id of the pointer type that can be used to point to this
// memory object.
uint32_t GetPointerTypeId(const CopyPropagateArrays* pass) const {
analysis::DefUseManager* def_use_mgr =
analysis::TypeManager* type_mgr =
Instruction* var_pointer_inst =
uint32_t member_type_id = pass->GetMemberTypeId(
var_pointer_inst->GetSingleWordInOperand(1), GetAccessIds());
uint32_t member_pointer_type_id = type_mgr->FindPointerToType(
member_type_id, static_cast<SpvStorageClass>(
return member_pointer_type_id;
// Returns the storage class of the memory object.
SpvStorageClass GetStorageClass() const {
analysis::TypeManager* type_mgr =
const analysis::Pointer* pointer_type =
return pointer_type->storage_class();
// Returns true if |other| represents memory that is contains inside of the
// memory represented by |this|.
bool Contains(MemoryObject* other);
// The variable that owns this memory object.
Instruction* variable_inst_;
// The access chain to reach the particular member the memory object
// represents. It should be interpreted the same way the indices in an
// |OpAccessChain| are interpreted.
std::vector<uint32_t> access_chain_;
std::vector<uint32_t> GetAccessIds() const;
// Returns the memory object being stored to |var_inst| in the store
// instruction |store_inst|, if one exists, that can be used in place of
// |var_inst| in all of the loads of |var_inst|. This code is conservative
// and only identifies very simple cases. If no such memory object can be
// found, the return value is |nullptr|.
std::unique_ptr<CopyPropagateArrays::MemoryObject> FindSourceObjectIfPossible(
Instruction* var_inst, Instruction* store_inst);
// Replaces all loads of |var_inst| with a load from |source| instead.
// |insertion_pos| is a position where it is possible to construct the
// address of |source| and also dominates all of the loads of |var_inst|.
void PropagateObject(Instruction* var_inst, MemoryObject* source,
Instruction* insertion_pos);
// Returns true if all of the references to |ptr_inst| can be rewritten and
// are dominated by |store_inst|.
bool HasValidReferencesOnly(Instruction* ptr_inst, Instruction* store_inst);
// Returns a memory object that at one time was equivalent to the value in
// |result|. If no such memory object exists, the return value is |nullptr|.
std::unique_ptr<MemoryObject> GetSourceObjectIfAny(uint32_t result);
// Returns the memory object that is loaded by |load_inst|. If a memory
// object cannot be identified, the return value is |nullptr|. The opcode of
// |load_inst| must be |OpLoad|.
std::unique_ptr<MemoryObject> BuildMemoryObjectFromLoad(
Instruction* load_inst);
// Returns the memory object that at some point was equivalent to the result
// of |extract_inst|. If a memory object cannot be identified, the return
// value is |nullptr|. The opcode of |extract_inst| must be
// |OpCompositeExtract|.
std::unique_ptr<MemoryObject> BuildMemoryObjectFromExtract(
Instruction* extract_inst);
// Returns the memory object that at some point was equivalent to the result
// of |construct_inst|. If a memory object cannot be identified, the return
// value is |nullptr|. The opcode of |constuct_inst| must be
// |OpCompositeConstruct|.
std::unique_ptr<MemoryObject> BuildMemoryObjectFromCompositeConstruct(
Instruction* conststruct_inst);
// Returns the memory object that at some point was equivalent to the result
// of |insert_inst|. If a memory object cannot be identified, the return
// value is |nullptr\. The opcode of |insert_inst| must be
// |OpCompositeInsert|. This function looks for a series of
// |OpCompositeInsert| instructions that insert the elements one at a time in
// order from beginning to end.
std::unique_ptr<MemoryObject> BuildMemoryObjectFromInsert(
Instruction* insert_inst);
// Return true if |type_id| is a pointer type whose pointee type is an array.
bool IsPointerToArrayType(uint32_t type_id);
// Returns true of there are not stores using |ptr_inst| or something derived
// from it.
bool HasNoStores(Instruction* ptr_inst);
// Creates an |OpAccessChain| instruction whose result is a pointer the memory
// represented by |source|. The new instruction will be placed before
// |insertion_point|. |insertion_point| must be part of a function. Returns
// the new instruction.
Instruction* BuildNewAccessChain(Instruction* insertion_point,
MemoryObject* source) const;
// Rewrites all uses of |original_ptr| to use |new_pointer_inst| updating
// types of other instructions as needed. This function should not be called
// if |CanUpdateUses(original_ptr_inst, new_pointer_inst->type_id())| returns
// false.
void UpdateUses(Instruction* original_ptr_inst,
Instruction* new_pointer_inst);
// Return true if |UpdateUses| is able to change all of the uses of
// |original_ptr_inst| to |type_id| and still have valid code.
bool CanUpdateUses(Instruction* original_ptr_inst, uint32_t type_id);
// Returns a store to |var_inst| that writes to the entire variable, and is
// the only store that does so. Note it does not look through OpAccessChain
// instruction, so partial stores are not considered.
Instruction* FindStoreInstruction(const Instruction* var_inst) const;
// Return the type id of the member of the type |id| access using
// |access_chain|. The elements of |access_chain| are to be interpreted the
// same way the indexes are used in an |OpCompositeExtract| instruction.
uint32_t GetMemberTypeId(uint32_t id,
const std::vector<uint32_t>& access_chain) const;
} // namespace opt
} // namespace spvtools