[wasm] Fix codegen issue for i64.add and i64.sub on ia32

test/mjsunit/regress/wasm/regression-5800.js

+// Copyright 2017 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.
+
+load("test/mjsunit/wasm/wasm-constants.js");
+load("test/mjsunit/wasm/wasm-module-builder.js");
+
+(function AddTest() {
+  let builder = new WasmModuleBuilder();
+
+  builder.addFunction("main", kSig_i_v)
+    .addBody([
+      kExprBlock, kWasmStmt,
+        kExprI64Const, 0,
+        kExprI64Const, 0x80, 0x80, 0x80, 0x80, 0x10,

[Mircea Trofin, 2017/01/18 21:01:56]

mind adding a comment explaining what's with these numbers? (leb of a 33rd bit
flipped on)

[Eric Holk, 2017/01/18 21:20:50]

Done.

+        kExprI64Add,
+        kExprI64Eqz,
+        kExprBrIf, 0,
+        kExprI32Const, 0,
+        kExprReturn,
+      kExprEnd,
+      kExprI32Const, 0
+    ])
+    .exportFunc();
+  let module = builder.instantiate();
+  assertEquals(0, module.exports.main());
+})();
+
+(function SubTest() {
+  let builder = new WasmModuleBuilder();
+
+  builder.addFunction("main", kSig_i_v)
+    .addBody([
+      kExprBlock, kWasmStmt,
+        kExprI64Const, 0,
+        kExprI64Const, 0x80, 0x80, 0x80, 0x80, 0x10,
+        kExprI64Sub,
+        kExprI64Eqz,
+        kExprBrIf, 0,
+        kExprI32Const, 0,
+        kExprReturn,
+      kExprEnd,
+      kExprI32Const, 0
+    ])
+    .exportFunc();
+  let module = builder.instantiate();
+  assertEquals(0, module.exports.main());
+})();