From 04b0526d60de4e9979fc486d2ba655247d211d0b Mon Sep 17 00:00:00 2001
From: David Srbecky <dsrbecky@google.com>
Date: Mon, 9 Nov 2015 18:05:48 +0000
Subject: Encode function signatures properly in DWARF.

The signatures were previously stored as plain string.
The proper way in DWARF is to store them as structured tree of tags.
(for example, DW_TAG_subprogram containing DW_TAG_formal_parameter)

Note that this makes the debug sections smaller since DWARF
signatures are actually more efficient than just plain strings.

Change-Id: I6afbce28340570666d8674d07c0e324aad561dd5
---
 compiler/dwarf/dedup_vector.h | 67 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)
 create mode 100644 compiler/dwarf/dedup_vector.h

(limited to 'compiler/dwarf/dedup_vector.h')

diff --git a/compiler/dwarf/dedup_vector.h b/compiler/dwarf/dedup_vector.h
new file mode 100644
index 0000000000..7fb21b76e2
--- /dev/null
+++ b/compiler/dwarf/dedup_vector.h
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * 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 ART_COMPILER_DWARF_DEDUP_VECTOR_H_
+#define ART_COMPILER_DWARF_DEDUP_VECTOR_H_
+
+#include <vector>
+#include <unordered_map>
+
+namespace art {
+namespace dwarf {
+  class DedupVector {
+   public:
+    // Returns an offset to previously inserted identical block of data,
+    // or appends the data at the end of the vector and returns offset to it.
+    size_t Insert(const uint8_t* ptr, size_t num_bytes) {
+      // See http://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
+      uint32_t hash = 2166136261u;
+      for (size_t i = 0; i < num_bytes; i++) {
+        hash = (hash ^ ptr[i]) * 16777619u;
+      }
+      // Try to find existing copy of the data.
+      const auto& range = hash_to_offset_.equal_range(hash);
+      for (auto it = range.first; it != range.second; ++it) {
+        const size_t offset = it->second;
+        if (offset + num_bytes <= vector_.size() &&
+            memcmp(vector_.data() + offset, ptr, num_bytes) == 0) {
+          return offset;
+        }
+      }
+      // Append the data at the end of the vector.
+      const size_t new_offset = vector_.size();
+      hash_to_offset_.emplace(hash, new_offset);
+      vector_.insert(vector_.end(), ptr, ptr + num_bytes);
+      return new_offset;
+    }
+
+    const std::vector<uint8_t>& Data() const { return vector_; }
+
+   private:
+    struct IdentityHash {
+      size_t operator()(uint32_t v) const { return v; }
+    };
+
+    // We store the full hash as the key to simplify growing of the table.
+    // It avoids storing or referencing the actual data in the hash-table.
+    std::unordered_multimap<uint32_t, size_t, IdentityHash> hash_to_offset_;
+
+    std::vector<uint8_t> vector_;
+  };
+}  // namespace dwarf
+}  // namespace art
+
+#endif  // ART_COMPILER_DWARF_DEDUP_VECTOR_H_
-- 
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