S390: Optimize VBPERM on the simulator

Change-Id: I70e117d38d81cec0e7687714211b1c503075e3ba
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2609411Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#71925}

src/execution/s390/simulator-s390.cc

@@ -3711,11 +3711,11 @@ EVALUATE(VBPERM) {
   USE(m5);
   USE(m6);
   uint16_t result_bits = 0;
+  unsigned __int128 src_bits =
+      *(reinterpret_cast<__int128*>(get_simd_register(r2).int8));
   for (int i = 0; i < kSimd128Size; i++) {
     result_bits <<= 1;
     uint8_t selected_bit_index = get_simd_register_by_lane<uint8_t>(r3, i);
-    unsigned __int128 src_bits =
-        *(reinterpret_cast<__int128*>(get_simd_register(r2).int8));
     if (selected_bit_index < (kSimd128Size * kBitsPerByte)) {
       unsigned __int128 bit_value =
           (src_bits << selected_bit_index) >> (kSimd128Size * kBitsPerByte - 1);