[wasm] Fix set_local appearing in unreachable code.

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

 // 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.
 
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "src/base/utils/random-number-generator.h"
 
@@ skipping 1666 matching lines @@
   BUILD(r, WASM_BLOCK(
                2, WASM_IF(WASM_GET_LOCAL(0), WASM_SET_LOCAL(0, WASM_I8(61))),
                WASM_GET_LOCAL(0)));
   FOR_INT32_INPUTS(i) {
     int32_t expected = *i ? 61 : *i;
     CHECK_EQ(expected, r.Call(*i));
   }
 }
 
 
+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;
   BUILD(r, WASM_IF_ELSE(WASM_GET_LOCAL(0),  // --
                         WASM_I8(11),        // --
                         WASM_I8(22)));      // --
   FOR_INT32_INPUTS(i) {
     int32_t expected = *i ? 11 : 22;
     CHECK_EQ(expected, r.Call(*i));
   }
@@ skipping 1912 matching lines @@
 TEST(Run_Wasm_F32CopySign) {
   WasmRunner<float> r(MachineType::Float32(), MachineType::Float32());
   BUILD(r, WASM_F32_COPYSIGN(WASM_GET_LOCAL(0), WASM_GET_LOCAL(1)));
 
   FOR_FLOAT32_INPUTS(i) {
     FOR_FLOAT32_INPUTS(j) { CheckFloatEq(copysign(*i, *j), r.Call(*i, *j)); }
   }
 }
 
 #endif