[wasm] Remove the module environment and signature as arguments to OpcodeArity.

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 17c84c6ac24121e7d7e43c451c64f80fd3472970..46e78a69f26285a157d1671a52b78c578597abe6 100644
--- a/src/wasm/ast-decoder.cc
+++ b/src/wasm/ast-decoder.cc
@@ -287,21 +287,19 @@ class WasmDecoder : public Decoder {
 
       case kExprCallFunction: {
         CallFunctionOperand operand(this, pc);
-        return static_cast<int>(
-            module_->GetFunctionSignature(operand.index)->parameter_count());
+        return operand.arity;

[ahaas, 2016/05/02 14:48:28]

Could the arity be calculated in a static function?

[titzer, 2016/05/02 14:57:31]

Not sure what value that would add, since this function already handles all
bytecodes. Or do you mean to suggest that this functionality should be instead
moved to the top-level functions OpcodeArity and OpcodeLength?

       }
       case kExprCallIndirect: {
         CallIndirectOperand operand(this, pc);
-        return 1 + static_cast<int>(
-                       module_->GetSignature(operand.index)->parameter_count());
+        return 1 + operand.arity;
       }
       case kExprCallImport: {
         CallImportOperand operand(this, pc);
-        return static_cast<int>(
-            module_->GetImportSignature(operand.index)->parameter_count());
+        return operand.arity;
       }
       case kExprReturn: {
-        return static_cast<int>(sig_->return_count());
+        ReturnArityOperand operand(this, pc);
+        return operand.arity;
       }
 
 #define DECLARE_OPCODE_CASE(name, opcode, sig) \
@@ -1523,9 +1521,8 @@ int OpcodeLength(const byte* pc, const byte* end) {
   return decoder.OpcodeLength(pc);
 }
 
-int OpcodeArity(ModuleEnv* module, FunctionSig* sig, const byte* pc,
-                const byte* end) {
-  WasmDecoder decoder(module, sig, pc, end);
+int OpcodeArity(const byte* pc, const byte* end) {
+  WasmDecoder decoder(nullptr, nullptr, pc, end);

[ahaas, 2016/05/02 14:48:28]

Could you make OpcodeArity a static function?

[titzer, 2016/05/02 14:57:31]

The decoder classes are not exposed through the header file, but instead a
top-level function, so that would require adding a wrapper class.

[ahaas, 2016/05/02 15:12:41]

What I mean is, I don't see a point why you have to make a WasmDecoder object to
call decoder.OpcodeArity. Could also just be a personal preference. 

   return decoder.OpcodeArity(pc);
 }