Fix several wasm warnings an a use after free.

src/wasm/ast-decoder.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_WASM_AST_DECODER_H_
 #define V8_WASM_AST_DECODER_H_
 
 #include "src/signature.h"
 #include "src/wasm/wasm-opcodes.h"
 #include "src/wasm/wasm-result.h"
@@ skipping 17 matching lines @@
   FunctionSig* sig;              // signature of this function
   uint32_t local_int32_count;    // number of int32 locals
   uint32_t local_int64_count;    // number of int64 locals
   uint32_t local_float32_count;  // number of float32 locals
   uint32_t local_float64_count;  // number of float64 locals
   uint32_t total_locals;         // sum of parameters and all locals
 
   bool IsValidLocal(uint32_t index) { return index < total_locals; }
   uint32_t GetLocalCount() { return total_locals; }
   LocalType GetLocalType(uint32_t index) {
-    if (index < sig->parameter_count()) return sig->GetParam(index);
-    index -= sig->parameter_count();
+    if (index < static_cast<uint32_t>(sig->parameter_count())) {
+      return sig->GetParam(index);
+    }
+    index -= static_cast<uint32_t>(sig->parameter_count());
     if (index < local_int32_count) return kAstI32;
     index -= local_int32_count;
     if (index < local_int64_count) return kAstI64;
     index -= local_int64_count;
     if (index < local_float32_count) return kAstF32;
     index -= local_float32_count;
     if (index < local_float64_count) return kAstF64;
     return kAstStmt;
   }
 
@@ skipping 55 matching lines @@
 // Computes the length of the opcode at the given address.
 int OpcodeLength(const byte* pc);
 
 // Computes the arity (number of sub-nodes) of the opcode at the given address.
 int OpcodeArity(FunctionEnv* env, const byte* pc);
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_AST_DECODER_H_