[kernel] Remove NNBD compilation mode dummy from kernel binary

Also clean up some of the magic constants around this.

TEST=CI

Change-Id: Ie02df874cb30761d5ea08ae52c1507cf25318280
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/416940
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>

pkg/front_end/test/binary_md_dill_reader.dart

@@ -4,6 +4,8 @@
 
 import "dart:math" as math;
 
+import "package:kernel/binary/tag.dart" show numberOfFixedFields;
+
 class BinaryMdDillReader {
   final String _binaryMdContent;
 
@@ -121,8 +123,7 @@ class BinaryMdDillReader {
     numLibs = _peekUint32();
 
     // Skip to the start of the index.
-    _binaryOffset = _dillContent.length -
-        ((numLibs + 1) + 12 /* number of fixed fields */) * 4;
+    _binaryOffset = _dillContent.length - numberOfFixedFields(numLibs) * 4;
 
     // Read index.
     binaryOffsetForSourceTable = _peekUint32();
@@ -143,7 +144,6 @@ class BinaryMdDillReader {
     _binaryOffset += 4;
     mainMethodReference = _peekUint32();
     _binaryOffset += 4;
-    /*int compilationMode = */ _peekUint32();
 
     _binaryOffset = binaryOffsetForStringTable;
     var saved = readingInstructions["ComponentFile"]!;
@@ -157,8 +157,7 @@ class BinaryMdDillReader {
     Map componentFile = _readBinary("ComponentFile", "");
     if (_binaryOffset != _dillContent.length) {
       throw "Didn't read the entire binary: "
-          "Only read $_binaryOffset of ${_dillContent.length} bytes. "
-          "($componentFile)";
+          "Only read $_binaryOffset of ${_dillContent.length} bytes.";
     }
     if (verboseLevel > 0) {
       print("Successfully read the dill file.");
@@ -537,8 +536,8 @@ class BinaryMdDillReader {
       } else if (what == "ComponentIndex" &&
           instruction == "Byte[] 8bitAlignment;") {
         // Special-case 8-byte alignment.
-        int sizeWithoutPadding = _binaryOffset +
-            ((numLibs + 1) + 10 /* number of fixed fields */) * 4;
+        int sizeWithoutPadding =
+            _binaryOffset + numberOfFixedFields(numLibs) * 4;
         int padding = 8 - sizeWithoutPadding % 8;
         if (padding == 8) padding = 0;
         _binaryOffset += padding;

pkg/kernel/binary.md

@@ -147,7 +147,7 @@ type CanonicalName {
 
 type ComponentFile {
   UInt32 magic = 0x90ABCDEF;
-  UInt32 formatVersion = 123;
+  UInt32 formatVersion = 124;
   Byte[10] shortSdkHash;
   List<String> problemsAsJson; // Described in problems.md.
   Library[] libraries;
@@ -188,7 +188,6 @@ type ComponentIndex {
   UInt32 binaryOffsetForStringTable;
   UInt32 binaryOffsetForStartOfComponentIndex;
   UInt32 mainMethodReference; // This is a ProcedureReference with a fixed-size integer.
-  UInt32 _dummy; // TODO(jensj): Previously the component mode. Remove this.
   UInt32[libraryCount + 1] libraryOffsets;
   UInt32 libraryCount;
   UInt32 componentFileSizeInBytes;

pkg/kernel/lib/binary/ast_from_binary.dart

@@ -67,8 +67,6 @@ class CompilationModeError {
 }
 
 class _ComponentIndex {
-  static const int numberOfFixedFields = 12;
-
   final int binaryOffsetForSourceTable;
   final int binaryOffsetForCanonicalNames;
   final int binaryOffsetForMetadataPayloads;
@@ -790,8 +788,7 @@ class BinaryBuilder {
     }
 
     // Skip to the start of the index.
-    _byteOffset -=
-        ((libraryCount + 1) + _ComponentIndex.numberOfFixedFields) * 4;
+    _byteOffset -= numberOfFixedFields(libraryCount) * 4;
 
     // Now read the component index.
     int binaryOffsetForSourceTable = _componentStartOffset + readUint32();
@@ -805,8 +802,6 @@ class BinaryBuilder {
     int binaryOffsetForStartOfComponentIndex =
         _componentStartOffset + readUint32();
     int mainMethodReference = readUint32();
-    // TODO(jensj): Previously the component mode. Remove this.
-    readUint32();
     for (int i = 0; i < libraryCount + 1; ++i) {
       libraryOffsets[i] = _componentStartOffset + readUint32();
     }

pkg/kernel/lib/binary/ast_to_binary.dart

@@ -805,11 +805,9 @@ class BinaryPrinter implements Visitor<void>, BinarySink {
     // is added before component index.
     const int kernelFileAlignment = 8;
 
-    // Keep this in sync with number of writeUInt32 below.
-    int numComponentIndexEntries = 10 + libraryOffsets.length + 3;
     int componentIndexOffset = getBufferOffset();
-
-    int unalignedSize = componentIndexOffset + numComponentIndexEntries * 4;
+    int unalignedSize =
+        componentIndexOffset + numberOfFixedFields(libraryOffsets.length) * 4;
     int padding =
         ((unalignedSize + kernelFileAlignment - 1) & -kernelFileAlignment) -
             unalignedSize;
@@ -817,7 +815,8 @@ class BinaryPrinter implements Visitor<void>, BinarySink {
       writeByte(0);
     }
 
-    // Fixed-size ints at the end used as an index.
+    // Fixed-size ints at the end used as an index. Including main there's
+    // [fixedFieldsBeforeLibraries] fields.
     assert(_binaryOffsetForSourceTable >= 0);
     writeUInt32(_binaryOffsetForSourceTable);
     assert(_binaryOffsetForConstantTable >= 0);
@@ -843,16 +842,17 @@ class BinaryPrinter implements Visitor<void>, BinarySink {
           _ensureCanonicalName(getNonNullableMemberReferenceGetter(mainMethod));
       writeUInt32(main.index + 1);
     }
-    // TODO(jensj): Previously the component mode. Remove this.
-    writeUInt32(0);
 
+    // Offset for the libraries.
     assert(libraryOffsets.length == libraries.length);
     for (int offset in libraryOffsets) {
       writeUInt32(offset);
     }
-    writeUInt32(_binaryOffsetForSourceTable); // end of last library.
-    writeUInt32(libraries.length);
+    // and the end of the last library.
+    writeUInt32(_binaryOffsetForSourceTable);
 
+    // And an additional [fixedFieldsAfterLibraries] fields.
+    writeUInt32(libraries.length);
     writeUInt32(getBufferOffset() + 4); // total size.
   }
 

pkg/kernel/lib/binary/tag.dart

@@ -226,7 +226,7 @@ class Tag {
   /// Internal version of kernel binary format.
   /// Bump it when making incompatible changes in kernel binaries.
   /// Keep in sync with runtime/vm/kernel_binary.h, pkg/kernel/binary.md.
-  static const int BinaryFormatVersion = 123;
+  static const int BinaryFormatVersion = 124;
 }
 
 abstract class ConstantTag {
@@ -274,3 +274,14 @@ bool isValidSdkHash(String sdkHash) {
       expectedSdkHash == sdkHashNull ||
       sdkHash == expectedSdkHash);
 }
+
+/// These should match with what is written in
+/// BinaryPrinter.writeComponentIndex.
+const int fixedFieldsBeforeLibraries = 9;
+const int fixedFieldsAfterLibraries = 2;
+int numberOfFixedFields(int numberOfLibraries) {
+  return fixedFieldsBeforeLibraries +
+      numberOfLibraries +
+      1 +
+      fixedFieldsAfterLibraries;
+}

runtime/vm/compiler/frontend/kernel_translation_helper.cc

@@ -3095,34 +3095,22 @@ TokenPosition KernelReaderHelper::ReadPosition() {
 
 intptr_t KernelReaderHelper::SourceTableSize() {
   AlternativeReadingScope alt(&reader_);
-  intptr_t library_count = reader_.ReadFromIndexNoReset(
-      reader_.size(), LibraryCountFieldCountFromEnd, 1, 0);
+  intptr_t library_count = reader_.ReadSingleFieldFromIndexNoReset(
+      reader_.size(), KernelFixedFieldsAfterLibraries);
 
-  const intptr_t count_from_first_library_offset =
-      SourceTableFieldCountFromFirstLibraryOffset;
-
-  intptr_t source_table_offset = reader_.ReadFromIndexNoReset(
-      reader_.size(),
-      LibraryCountFieldCountFromEnd + 1 + library_count + 1 +
-          count_from_first_library_offset,
-      1, 0);
+  intptr_t source_table_offset = reader_.ReadSingleFieldFromIndexNoReset(
+      reader_.size(), KernelNumberOfFixedFields(library_count));
   SetOffset(source_table_offset);  // read source table offset.
   return reader_.ReadUInt32();     // read source table size.
 }
 
 intptr_t KernelReaderHelper::GetOffsetForSourceInfo(intptr_t index) {
   AlternativeReadingScope alt(&reader_);
-  intptr_t library_count = reader_.ReadFromIndexNoReset(
-      reader_.size(), LibraryCountFieldCountFromEnd, 1, 0);
+  intptr_t library_count = reader_.ReadSingleFieldFromIndexNoReset(
+      reader_.size(), KernelFixedFieldsAfterLibraries);
 
-  const intptr_t count_from_first_library_offset =
-      SourceTableFieldCountFromFirstLibraryOffset;
-
-  intptr_t source_table_offset = reader_.ReadFromIndexNoReset(
-      reader_.size(),
-      LibraryCountFieldCountFromEnd + 1 + library_count + 1 +
-          count_from_first_library_offset,
-      1, 0);
+  intptr_t source_table_offset = reader_.ReadSingleFieldFromIndexNoReset(
+      reader_.size(), KernelNumberOfFixedFields(library_count));
   intptr_t next_field_offset = reader_.ReadUInt32();
   SetOffset(source_table_offset);
   intptr_t size = reader_.ReadUInt32();  // read source table size.

runtime/vm/kernel_binary.cc

@@ -154,15 +154,10 @@ std::unique_ptr<Program> Program::ReadFrom(Reader* reader, const char** error) {
   program->single_program_ = subprogram_count == 1;
 
   // Read backwards at the end.
-  program->library_count_ = reader->ReadFromIndexNoReset(
-      reader->size_, LibraryCountFieldCountFromEnd, 1, 0);
-  intptr_t count_from_first_library_offset =
-      SourceTableFieldCountFromFirstLibraryOffset;
-  program->source_table_offset_ = reader->ReadFromIndexNoReset(
-      reader->size_,
-      LibraryCountFieldCountFromEnd + 1 + program->library_count_ + 1 +
-          count_from_first_library_offset,
-      1, 0);
+  program->library_count_ = reader->ReadSingleFieldFromIndexNoReset(
+      reader->size_, KernelFixedFieldsAfterLibraries);
+  program->source_table_offset_ = reader->ReadSingleFieldFromIndexNoReset(
+      reader->size_, KernelNumberOfFixedFields(program->library_count_));
   program->constant_table_offset_ = reader->ReadUInt32();
   reader->ReadUInt32();  // offset for constant table index.
   program->name_table_offset_ = reader->ReadUInt32();
@@ -174,8 +169,6 @@ std::unique_ptr<Program> Program::ReadFrom(Reader* reader, const char** error) {
   program->component_index_offset_ = reader->ReadUInt32();
 
   program->main_method_reference_ = NameIndex(reader->ReadUInt32() - 1);
-  // TODO(jensj): Remove this.
-  reader->ReadUInt32();  // Read and ignore NNBD compilation mode.
 
   return program;
 }

runtime/vm/kernel_binary.h

@@ -18,7 +18,7 @@ namespace kernel {
 // package:kernel/binary.md.
 
 static const uint32_t kMagicProgramFile = 0x90ABCDEFu;
-static const uint32_t kSupportedKernelFormatVersion = 123;
+static const uint32_t kSupportedKernelFormatVersion = 124;
 
 // Keep in sync with package:kernel/lib/binary/tag.dart
 #define KERNEL_TAG_LIST(V)                                                     \
@@ -271,9 +271,15 @@ enum class FunctionAccessKind {
 };
 
 static constexpr int SpecializedIntLiteralBias = 3;
-static constexpr int LibraryCountFieldCountFromEnd = 1;
 static constexpr int KernelFormatVersionOffset = 4;
-static constexpr int SourceTableFieldCountFromFirstLibraryOffset = 9;
+
+// These should be kept in sync with the constants in kernels tag.dart.
+static constexpr int KernelFixedFieldsBeforeLibraries = 9;
+static constexpr int KernelFixedFieldsAfterLibraries = 2;
+static inline int KernelNumberOfFixedFields(int numberOfLibraries) {
+  return KernelFixedFieldsBeforeLibraries + numberOfLibraries + 1 +
+         KernelFixedFieldsAfterLibraries;
+}
 
 static constexpr int HeaderSize = 8;  // 'magic', 'formatVersion'.
 
@@ -310,6 +316,12 @@ class Reader : public ValueObject {
     return ReadUInt32();
   }
 
+  uint32_t ReadSingleFieldFromIndexNoReset(intptr_t end_offset,
+                                           intptr_t fields_before) {
+    offset_ = end_offset - fields_before * 4;
+    return ReadUInt32();
+  }
+
   uint32_t ReadUInt32() {
     uint32_t value = ReadUInt32At(offset_);
     offset_ += 4;

runtime/vm/kernel_loader.h

@@ -273,7 +273,7 @@ class KernelLoader : public ValueObject {
   intptr_t library_offset(intptr_t index) {
     kernel::Reader reader(program_->binary());
     return reader.ReadFromIndexNoReset(reader.size(),
-                                       LibraryCountFieldCountFromEnd + 1,
+                                       KernelFixedFieldsAfterLibraries,
                                        program_->library_count() + 1, index);
   }