[wasm] Fix set_local appearing in unreachable code.

test/cctest/wasm/test-run-wasm.cc

Index: test/cctest/wasm/test-run-wasm.cc
diff --git a/test/cctest/wasm/test-run-wasm.cc b/test/cctest/wasm/test-run-wasm.cc
index cc9663974b6b0252c56a24f5db4420dfe7abdb79..fe440caf2508748f939738df90e8a4afbfa88dbe 100644
--- a/test/cctest/wasm/test-run-wasm.cc
+++ b/test/cctest/wasm/test-run-wasm.cc
@@ -1684,6 +1684,14 @@ TEST(Run_Wasm_Block_If_P_assign) {
 }
 
 
+TEST(Run_Wasm_DanglingAssign) {
+  WasmRunner<int32_t> r(MachineType::Int32());
+  // { return 0; p0 = 0; }
+  BUILD(r, WASM_BLOCK(2, WASM_RETURN(WASM_ZERO), WASM_SET_LOCAL(0, WASM_ZERO)));

[ahaas, 2016/01/11 11:40:52]

Nit: Maybe we could return a magic number instead of zero, just to avoid
accidental passes.

+  CHECK_EQ(0, r.Call(1));
+}
+
+
 TEST(Run_Wasm_ExprIf_P) {
   WasmRunner<int32_t> r(MachineType::Int32());
   // p0 ? 11 : 22;