[wasm] Fix empty asm.js function in ASM->WASM.

R=ahaas@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1574263002

Cr-Commit-Position: refs/heads/master@{#33238}

src/wasm/encoder.cc

@@ -157,8 +157,10 @@ WasmFunctionEncoder* WasmFunctionBuilder::Build(Zone* zone,
                                                 WasmModuleBuilder* mb) const {
   WasmFunctionEncoder* e =
       new (zone) WasmFunctionEncoder(zone, return_type_, exported_, external_);
-  auto var_index = new uint16_t[locals_.size()];
+  uint16_t* var_index = zone->NewArray<uint16_t>(locals_.size());
   IndexVars(e, var_index);
+  if (body_.size() > 0) {
+    // TODO(titzer): iterate over local indexes, not the bytes.
     const byte* start = &body_[0];
     const byte* end = start + body_.size();
     size_t local_index = 0;
@@ -180,6 +182,7 @@ WasmFunctionEncoder* WasmFunctionBuilder::Build(Zone* zone,
         i++;
       }
     }
+  }
   FunctionSig::Builder sig(zone, return_type_ == kAstStmt ? 0 : 1,
                            e->params_.size());
   if (return_type_ != kAstStmt) {
@@ -189,7 +192,6 @@ WasmFunctionEncoder* WasmFunctionBuilder::Build(Zone* zone,
     sig.AddParam(static_cast<LocalType>(e->params_[i]));
   }
   e->signature_index_ = mb->AddSignature(sig.Build());
-  delete[] var_index;
   e->name_.insert(e->name_.begin(), name_.begin(), name_.end());
   return e;
 }
@@ -295,9 +297,11 @@ void WasmFunctionEncoder::Serialize(byte* buffer, byte** header,
 
   if (!external_) {
     EmitUint16(header, static_cast<uint16_t>(body_.size()));
+    if (body_.size() > 0) {
       std::memcpy(*header, &body_[0], body_.size());
       (*header) += body_.size();
     }
+  }
 }
 
 

test/mjsunit/wasm/asm-wasm.js

@@ -4,6 +4,19 @@
 
 // Flags: --expose-wasm
 
+function EmptyTest() {
+  "use asm";
+  function caller() {
+    empty();
+    return 11;
+  }
+  function empty() {
+  }
+  return {caller: caller};
+}
+
+assertEquals(11, WASM.asmCompileRun(EmptyTest.toString()));
+
 function IntTest() {
   "use asm";
   function sum(a, b) {