text: // Copyright (c) 2019 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
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  #ifndef SOURCE_OPT_DESC_SROA_H_
  #define SOURCE_OPT_DESC_SROA_H_
  
  #include <cstdio>
  #include <memory>
  #include <queue>
  #include <unordered_map>
  #include <unordered_set>
  #include <vector>
  
  #include "source/opt/function.h"
  #include "source/opt/pass.h"
  #include "source/opt/type_manager.h"
  
  namespace spvtools {
  namespace opt {
  
  // Documented in optimizer.hpp
  class DescriptorScalarReplacement : public Pass {
   public:
    DescriptorScalarReplacement() {}
  
    const char* name() const override { return "descriptor-scalar-replacement"; }
  
    Status Process() override;
  
    IRContext::Analysis GetPreservedAnalyses() override {
      return IRContext::kAnalysisDefUse |
             IRContext::kAnalysisInstrToBlockMapping |
             IRContext::kAnalysisCombinators | IRContext::kAnalysisCFG |
             IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
    }
  
   private:
    // Returns true if |var| is an OpVariable instruction that represents a
    // descriptor array.  These are the variables that we want to replace.
    bool IsCandidate(Instruction* var);
  
    // Replaces all references to |var| by new variables, one for each element of
    // the array |var|.  The binding for the new variables corresponding to
    // element i will be the binding of |var| plus i.  Returns true if successful.
    bool ReplaceCandidate(Instruction* var);
  
    // Replaces the base address |var| in the OpAccessChain or
    // OpInBoundsAccessChain instruction |use| by the variable that the access
    // chain accesses.  The first index in |use| must be an |OpConstant|.  Returns
    // |true| if successful.
    bool ReplaceAccessChain(Instruction* var, Instruction* use);
  
    // Replaces the given compososite variable |var| loaded by OpLoad |value| with
    // replacement variables, one for each component that's accessed in the
    // shader. Assumes that |value| is only used by OpCompositeExtract
    // instructions, one index at a time. Returns true on success, and false
    // otherwise.
    bool ReplaceLoadedValue(Instruction* var, Instruction* value);
  
    // Replaces the given OpCompositeExtract |extract| and all of its references
    // with an OpLoad of a replacement variable. |var| is the variable with
    // composite type whose value is being used by |extract|. Assumes that
    // |extract| is extracting one index only. Returns true on success, and false
    // otherwise.
    bool ReplaceCompositeExtract(Instruction* var, Instruction* extract);
  
    // Returns the id of the variable that will be used to replace the |idx|th
    // element of |var|.  The variable is created if it has not already been
    // created.
    uint32_t GetReplacementVariable(Instruction* var, uint32_t idx);
  
    // Returns the id of a new variable that can be used to replace the |idx|th
    // element of |var|.
    uint32_t CreateReplacementVariable(Instruction* var, uint32_t idx);
  
    // Returns the number of bindings used by the given |type_id|.
    // All types are considered to use 1 binding slot, except:
    // 1- A pointer type consumes as many binding numbers as its pointee.
    // 2- An array of size N consumes N*M binding numbers, where M is the number
    // of bindings used by each array element.
    // 3- The number of bindings consumed by a structure is the sum of the
    // bindings used by its members.
    uint32_t GetNumBindingsUsedByType(uint32_t type_id);
  
    // Returns true if |type| is a type that could be used for a structured buffer
    // as opposed to a type that would be used for a structure of resource
    // descriptors.
    bool IsTypeOfStructuredBuffer(const Instruction* type) const;
  
    // A map from an OpVariable instruction to the set of variables that will be
    // used to replace it. The entry |replacement_variables_[var][i]| is the id of
    // a variable that will be used in the place of the the ith element of the
    // array |var|. If the entry is |0|, then the variable has not been
    // created yet.
    std::map<Instruction*, std::vector<uint32_t>> replacement_variables_;
  };
  
  }  // namespace opt
  }  // namespace spvtools
  
  #endif  // SOURCE_OPT_DESC_SROA_H_
  