[wasm] Implement 128-bit endian swap for simd type

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

Index: test/cctest/wasm/test-run-wasm-simd.cc
diff --git a/test/cctest/wasm/test-run-wasm-simd.cc b/test/cctest/wasm/test-run-wasm-simd.cc
index 58f1d6559c622a9b87e4054a8e23b981986c3e90..38042e735ef68c2f8092c2fc81bed0c03f26c8a5 100644
--- a/test/cctest/wasm/test-run-wasm-simd.cc
+++ b/test/cctest/wasm/test-run-wasm-simd.cc
@@ -2209,7 +2209,11 @@ WASM_EXEC_COMPILED_TEST(SimdLoadStoreLoad) {
 
   FOR_INT32_INPUTS(i) {
     int32_t expected = *i;
+#if defined(V8_TARGET_LITTLE_ENDIAN)
     r.module().WriteMemory(&memory[0], expected);
+#else
+    r.module().WriteMemory(&memory[3], expected);

[Clemens Hammacher, 2017/04/26 18:40:05]

This does not look like the right fix. Storing the lanes in different order
would make endianess observable, breaking platform independence of wasm code.
I am no expert in the SIMD proposal, though.

Bill, can you comment on that?

[bbudge, 2017/04/26 20:14:12]

You're right Clemens. SIMD shouldn't be any different than the rest of
WebAssembly. Loads and stores are always in little-endian order, so this test
shouldn't change.

+#endif
     CHECK_EQ(expected, r.Call());
   }
 }