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source/3rdparty/vulkan/source/opt/dead_variable_elimination.h

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+// Copyright (c) 2017 Google Inc.
+//
+// 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_DEAD_VARIABLE_ELIMINATION_H_
+#define SOURCE_OPT_DEAD_VARIABLE_ELIMINATION_H_
+
+#include <climits>
+#include <unordered_map>
+
+#include "source/opt/decoration_manager.h"
+#include "source/opt/mem_pass.h"
+
+namespace spvtools {
+namespace opt {
+
+class DeadVariableElimination : public MemPass {
+ public:
+  const char* name() const override { return "eliminate-dead-variables"; }
+  Status Process() override;
+
+  IRContext::Analysis GetPreservedAnalyses() override {
+    return IRContext::kAnalysisDefUse | IRContext::kAnalysisConstants |
+           IRContext::kAnalysisTypes;
+  }
+
+ private:
+  // Deletes the OpVariable instruction who result id is |result_id|.
+  void DeleteVariable(uint32_t result_id);
+
+  // Keeps track of the number of references of an id.  Once that value is 0, it
+  // is safe to remove the corresponding instruction.
+  //
+  // Note that the special value kMustKeep is used to indicate that the
+  // instruction cannot be deleted for reasons other that is being explicitly
+  // referenced.
+  std::unordered_map<uint32_t, size_t> reference_count_;
+
+  // Special value used to indicate that an id cannot be safely deleted.
+  enum { kMustKeep = INT_MAX };
+};
+
+}  // namespace opt
+}  // namespace spvtools
+
+#endif  // SOURCE_OPT_DEAD_VARIABLE_ELIMINATION_H_