Optimizing: Improve const-string code generation.

For strings in the boot image, use either direct pointers
or pc-relative addresses. For other strings, use PC-relative
access to the dex cache arrays for AOT and direct address of
the string's dex cache slot for JIT.

For aosp_flounder-userdebug:
  - 32-bit boot.oat: -692KiB (-0.9%)
  - 64-bit boot.oat: -948KiB (-1.1%)
  - 32-bit dalvik cache total: -900KiB (-0.9%)
  - 64-bit dalvik cache total: -3672KiB (-1.5%)
    (contains more files than the 32-bit dalvik cache)
For aosp_flounder-userdebug forced to compile PIC:
  - 32-bit boot.oat: -380KiB (-0.5%)
  - 64-bit boot.oat: -928KiB (-1.0%)
  - 32-bit dalvik cache total: -468KiB (-0.4%)
  - 64-bit dalvik cache total: -1928KiB (-0.8%)
    (contains more files than the 32-bit dalvik cache)

Bug: 26884697
Change-Id: Iec7266ce67e6fedc107be78fab2e742a8dab2696

1 files changed, 64 insertions, 0 deletions

diff --git a/compiler/utils/string_reference.h b/compiler/utils/string_reference.h
new file mode 100644
index 0000000000..72552f21aa
--- /dev/null
+++ b/compiler/utils/string_reference.h
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2016 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_UTILS_STRING_REFERENCE_H_
+#define ART_COMPILER_UTILS_STRING_REFERENCE_H_
+
+#include <stdint.h>
+
+#include "base/logging.h"
+#include "utf-inl.h"
+
+namespace art {
+
+class DexFile;
+
+// A string is uniquely located by its DexFile and the string_ids_ table index into that DexFile.
+struct StringReference {
+  StringReference(const DexFile* file, uint32_t index) : dex_file(file), string_index(index) { }
+
+  const DexFile* dex_file;
+  uint32_t string_index;
+};
+
+// Compare the actual referenced string values. Used for string reference deduplication.
+struct StringReferenceValueComparator {
+  bool operator()(StringReference sr1, StringReference sr2) const {
+    // Note that we want to deduplicate identical strings even if they are referenced
+    // by different dex files, so we need some (any) total ordering of strings, rather
+    // than references. However, the references should usually be from the same dex file,
+    // so we choose the dex file string ordering so that we can simply compare indexes
+    // and avoid the costly string comparison in the most common case.
+    if (sr1.dex_file == sr2.dex_file) {
+      // Use the string order enforced by the dex file verifier.
+      DCHECK_EQ(
+          sr1.string_index < sr2.string_index,
+          CompareModifiedUtf8ToModifiedUtf8AsUtf16CodePointValues(
+              sr1.dex_file->GetStringData(sr1.dex_file->GetStringId(sr1.string_index)),
+              sr1.dex_file->GetStringData(sr2.dex_file->GetStringId(sr2.string_index))) < 0);
+      return sr1.string_index < sr2.string_index;
+    } else {
+      // Cannot compare indexes, so do the string comparison.
+      return CompareModifiedUtf8ToModifiedUtf8AsUtf16CodePointValues(
+          sr1.dex_file->GetStringData(sr1.dex_file->GetStringId(sr1.string_index)),
+          sr1.dex_file->GetStringData(sr2.dex_file->GetStringId(sr2.string_index))) < 0;
+    }
+  }
+};
+
+}  // namespace art
+
+#endif  // ART_COMPILER_UTILS_STRING_REFERENCE_H_