[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,
+        // 0x80 ... 0x10 is the LEB encoding of 0x100000000. This is chosen so
+        // that the 64-bit constant has a non-zero top half. In this bug, the
+        // top half was clobbering eax, leading to the function return 1 rather
+        // than 0.
+        kExprI64Const, 0x80, 0x80, 0x80, 0x80, 0x10,
+        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,
+        // 0x80 ... 0x10 is the LEB encoding of 0x100000000. This is chosen so
+        // that the 64-bit constant has a non-zero top half. In this bug, the
+        // top half was clobbering eax, leading to the function return 1 rather
+        // than 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());
+})();