[x64] Fix invalid REX prefix for pslld, psrld and friends.

R=epertoso@chromium.org

Review-Url: https://codereview.chromium.org/2026633004
Cr-Commit-Position: refs/heads/master@{#36631}

src/x64/assembler-x64-inl.h

@@ -179,9 +179,8 @@ void Assembler::emit_optional_rex_32(Register rm_reg) {
   if (rm_reg.high_bit()) emit(0x41);
 }
 
-void Assembler::emit_optional_rex_32(XMMRegister reg) {
-  byte rex_bits = (reg.code() & 0x8) >> 1;
-  if (rex_bits != 0) emit(0x40 | rex_bits);
+void Assembler::emit_optional_rex_32(XMMRegister rm_reg) {
+  if (rm_reg.high_bit()) emit(0x41);
 }
 
 void Assembler::emit_optional_rex_32(const Operand& op) {

test/cctest/test-assembler-x64.cc

@@ -2296,4 +2296,24 @@ TEST(AssemblerX64JumpTables2) {
   }
 }
 
+TEST(AssemblerX64PslldWithXmm15) {
+  CcTest::InitializeVM();
+  // Allocate an executable page of memory.
+  size_t actual_size;
+  byte* buffer = static_cast<byte*>(v8::base::OS::Allocate(
+      Assembler::kMinimalBufferSize, &actual_size, true));
+  CHECK(buffer);
+  Assembler assm(CcTest::i_isolate(), buffer, static_cast<int>(actual_size));
+
+  __ movq(xmm15, arg1);
+  __ pslld(xmm15, 1);
+  __ movq(rax, xmm15);
+  __ ret(0);
+
+  CodeDesc desc;
+  assm.GetCode(&desc);
+  uint64_t result = FUNCTION_CAST<F5>(buffer)(V8_UINT64_C(0x1122334455667788));
+  CHECK_EQ(V8_UINT64_C(0x22446688aaccef10), result);
+}
+
 #undef __