[wasm] add atomic opcodes

src/wasm/ast-decoder.cc

Index: src/wasm/ast-decoder.cc
diff --git a/src/wasm/ast-decoder.cc b/src/wasm/ast-decoder.cc
index 4e19d0f6b6a1894851890ffb5bedbac1790f9c99..64f48645a53adec12ee858f48ab9929390663c2a 100644
--- a/src/wasm/ast-decoder.cc
+++ b/src/wasm/ast-decoder.cc
@@ -1146,6 +1146,24 @@ class WasmFullDecoder : public WasmDecoder {
             len += DecodeSimdOpcode(opcode);
             break;
           }
+          case kAtomicPrefix: {
+            if (!module_ || module_->origin != kAsmJsOrigin) {
+              error("Atomics are allowed only in AsmJs modules");
+              break;
+            }
+            if (!FLAG_wasm_atomics_prototype) {

[titzer, 2016/10/26 08:07:17]

You can use the macro for this check.

[aseemgarg, 2016/10/26 19:53:57]

The CHECK_PROTOTYPE_OPCODE checks that module origin is not asmjs. In this case
we want the origin to be asmjs. 
I can create a new Macro for that but since it is used at only one place yet,
don't really see the point. 

+              error("Invalid opcode (enable with --wasm_atomics_prototype)");
+              break;
+            }
+            len++;

[titzer, 2016/10/26 08:07:17]

Please don't do len++, but set len = 2.

[aseemgarg, 2016/10/26 19:53:57]

Done. Can you explain why?

+            byte atomic_index = checked_read_u8(pc_, 1, "atomic index");

[titzer, 2016/10/26 08:07:17]

"atomic opcode" instead of "atomic index"

[aseemgarg, 2016/10/26 19:53:57]

Done.

+            opcode = static_cast<WasmOpcode>(opcode << 8 | atomic_index);
+            sig = WasmOpcodes::AtomicSignature(opcode);
+            if (sig) {
+              BuildAtomicOperator(opcode);
+            }
+            break;
+          }
           default: {
             // Deal with special asmjs opcodes.
             if (module_ && module_->origin == kAsmJsOrigin) {
@@ -1328,6 +1346,8 @@ class WasmFullDecoder : public WasmDecoder {
     return len;
   }
 
+  void BuildAtomicOperator(WasmOpcode opcode) { UNIMPLEMENTED(); }
+
   void DoReturn() {
     int count = static_cast<int>(sig_->return_count());
     TFNode** buffer = nullptr;