Replace __init__ function in asm-wasm-builder with the start function section

BUG= https://code.google.com/p/v8/issues/detail?id=4203
TEST=mjsunit/asm-wasm
R=titzer@chromium.org,bradnelson@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/1750153002

Cr-Commit-Position: refs/heads/master@{#34375}

src/wasm/asm-wasm-builder.cc

@@ -66,12 +66,10 @@ class AsmWasmBuilderImpl : public AstVisitor {
   }
 
   void InitializeInitFunction() {
-    unsigned char init[] = "__init__";
     init_function_index_ = builder_->AddFunction();
     current_function_builder_ = builder_->FunctionAt(init_function_index_);
-    current_function_builder_->SetName(init, 8);
     current_function_builder_->ReturnType(kAstStmt);
-    current_function_builder_->Exported(1);
+    builder_->MarkStartFunction(init_function_index_);
     current_function_builder_ = nullptr;
   }
 

src/wasm/encoder.cc

@@ -333,7 +333,6 @@ void WasmDataSegmentEncoder::Serialize(byte* buffer, byte** header,
   (*body) += data_.size();
 }
 
-
 WasmModuleBuilder::WasmModuleBuilder(Zone* zone)
     : zone_(zone),
       signatures_(zone),
@@ -341,8 +340,8 @@ WasmModuleBuilder::WasmModuleBuilder(Zone* zone)
       data_segments_(zone),
       indirect_functions_(zone),
       globals_(zone),
-      signature_map_(zone) {}
-
+      signature_map_(zone),
+      start_function_index_(-1) {}
 
 uint16_t WasmModuleBuilder::AddFunction() {
   functions_.push_back(new (zone_) WasmFunctionBuilder(zone_));
@@ -399,6 +398,9 @@ void WasmModuleBuilder::AddIndirectFunction(uint16_t index) {
   indirect_functions_.push_back(index);
 }
 
+void WasmModuleBuilder::MarkStartFunction(uint16_t index) {
+  start_function_index_ = index;
+}
 
 WasmModuleWriter* WasmModuleBuilder::Build(Zone* zone) {
   WasmModuleWriter* writer = new (zone) WasmModuleWriter(zone);
@@ -417,6 +419,7 @@ WasmModuleWriter* WasmModuleBuilder::Build(Zone* zone) {
   for (auto global : globals_) {
     writer->globals_.push_back(global);
   }
+  writer->start_function_index_ = start_function_index_;
   return writer;
 }
 
@@ -434,6 +437,14 @@ WasmModuleWriter::WasmModuleWriter(Zone* zone)
       indirect_functions_(zone),
       globals_(zone) {}
 
+size_t SizeOfVarInt(size_t value) {
+  size_t size = 0;
+  do {
+    size++;
+    value = value >> 7;
+  } while (value > 0);
+  return size;
+}
 
 struct Sizes {
   size_t header_size;
@@ -449,10 +460,7 @@ struct Sizes {
   void AddSection(size_t size) {
     if (size > 0) {
       Add(1, 0);
-      while (size > 0) {
-        Add(1, 0);
-        size = size >> 7;
-      }
+      Add(SizeOfVarInt(size), 0);
     }
   }
 };
@@ -482,6 +490,11 @@ WasmModuleIndex* WasmModuleWriter::WriteTo(Zone* zone) const {
               function->NameSize());
   }
 
+  if (start_function_index_ >= 0) {
+    sizes.Add(1, 0);
+    sizes.Add(SizeOfVarInt(start_function_index_), 0);
+  }
+
   sizes.AddSection(data_segments_.size());
   for (auto segment : data_segments_) {
     sizes.Add(segment->HeaderSize(), segment->BodySize());
@@ -547,6 +560,12 @@ WasmModuleIndex* WasmModuleWriter::WriteTo(Zone* zone) const {
     }
   }
 
+  // -- emit start function index ----------------------------------------------
+  if (start_function_index_ >= 0) {
+    EmitUint8(&header, kDeclStartFunction);
+    EmitVarInt(&header, start_function_index_);
+  }
+
   // -- emit data segments -----------------------------------------------------
   if (data_segments_.size() > 0) {
     EmitUint8(&header, kDeclDataSegments);

src/wasm/encoder.h

@@ -120,6 +120,7 @@ class WasmModuleWriter : public ZoneObject {
   ZoneVector<FunctionSig*> signatures_;
   ZoneVector<uint16_t> indirect_functions_;
   ZoneVector<std::pair<MachineType, bool>> globals_;
+  int start_function_index_;
 };
 
 class WasmModuleBuilder : public ZoneObject {
@@ -131,6 +132,7 @@ class WasmModuleBuilder : public ZoneObject {
   void AddDataSegment(WasmDataSegmentEncoder* data);
   uint16_t AddSignature(FunctionSig* sig);
   void AddIndirectFunction(uint16_t index);
+  void MarkStartFunction(uint16_t index);
   WasmModuleWriter* Build(Zone* zone);
 
   struct CompareFunctionSigs {
@@ -146,6 +148,7 @@ class WasmModuleBuilder : public ZoneObject {
   ZoneVector<uint16_t> indirect_functions_;
   ZoneVector<std::pair<MachineType, bool>> globals_;
   SignatureMap signature_map_;
+  int start_function_index_;
 };
 
 std::vector<uint8_t> UnsignedLEB128From(uint32_t result);

test/mjsunit/wasm/asm-wasm.js

@@ -415,7 +415,6 @@ function TestInt32HeapAccessExternal() {
   var memory_int32 = new Int32Array(memory);
   var module = _WASMEXP_.instantiateModuleFromAsm(
       TestInt32HeapAccess.toString(), null, memory);
-  module.__init__();
   assertEquals(7, module.caller());
   assertEquals(7, memory_int32[2]);
 }
@@ -439,7 +438,6 @@ function TestHeapAccessIntTypes() {
     var memory = new ArrayBuffer(1024);
     var memory_view = new types[i][0](memory);
     var module = _WASMEXP_.instantiateModuleFromAsm(code, null, memory);
-    module.__init__();
     assertEquals(7, module.caller());
     assertEquals(7, memory_view[2]);
     assertEquals(7, _WASMEXP_.instantiateModuleFromAsm(code).caller());
@@ -480,7 +478,6 @@ function TestFloatHeapAccessExternal() {
   var memory_float64 = new Float64Array(memory);
   var module = _WASMEXP_.instantiateModuleFromAsm(
       TestFloatHeapAccess.toString(), null, memory);
-  module.__init__();
   assertEquals(1, module.caller());
   assertEquals(9.0, memory_float64[1]);
 }
@@ -656,7 +653,6 @@ function TestGlobalsWithInit() {
 }
 
 var module = _WASMEXP_.instantiateModuleFromAsm(TestGlobalsWithInit.toString());
-module.__init__();
 assertEquals(77.5, module.add());
 
 
@@ -879,7 +875,6 @@ function TestInitFunctionWithNoGlobals() {
 
 var module = _WASMEXP_.instantiateModuleFromAsm(
     TestInitFunctionWithNoGlobals.toString());
-module.__init__();
 assertEquals(51, module.caller());
 
 
@@ -893,7 +888,6 @@ function TestExportNameDifferentFromFunctionName() {
 
 var module = _WASMEXP_.instantiateModuleFromAsm(
     TestExportNameDifferentFromFunctionName.toString());
-module.__init__();
 assertEquals(55, module.alt_caller());
 
 
@@ -988,7 +982,6 @@ function TestFunctionTable() {
 }
 
 var module = _WASMEXP_.instantiateModuleFromAsm(TestFunctionTable.toString());
-module.__init__();
 assertEquals(55, module.caller(0, 0, 33, 22));
 assertEquals(11, module.caller(0, 1, 33, 22));
 assertEquals(9, module.caller(0, 2, 54, 45));
@@ -1036,7 +1029,6 @@ function TestForeignFunctions() {
   var module = _WASMEXP_.instantiateModuleFromAsm(AsmModule.toString(),
                                                   foreign, null);
 
-  module.__init__();
   assertEquals(103, module.caller(23, 103));
 }
 
@@ -1076,7 +1068,6 @@ function TestForeignFunctionMultipleUse() {
   var module = _WASMEXP_.instantiateModuleFromAsm(AsmModule.toString(),
                                                   foreign, null);
 
-  module.__init__();
   assertEquals(89, module.caller(83, 83.25));
 }
 
@@ -1114,7 +1105,6 @@ function TestForeignVariables() {
   function TestCase(env, i1, f1, i2, f2) {
     var module = _WASMEXP_.instantiateModuleFromAsm(
         AsmModule.toString(), env);
-    module.__init__();
     assertEquals(i1, module.geti1());
     assertEquals(f1, module.getf1());
     assertEquals(i2, module.geti2());
@@ -1237,7 +1227,6 @@ TestForeignVariables();
 
   var m = _WASMEXP_.instantiateModuleFromAsm(
       Module.toString(), { x: 4, y: 11 });
-  m.__init__();
   assertEquals(15, m.test());
 })();