message: When we know RDX is unavailable, use RAX instead. Should be fine here.
diff: @@ -2874,15 +2874,15 @@ impl FunctionCodeGenerator<CodegenError> for X64FunctionCode {
  a.emit_mov(Size::S64, Location::Memory(GPR::RDX, 0), Location::XMM(x));
  }
  XMMOrMemory::Memory(base, disp) => {
  - // TODO: What if base == RDX?
  + let neg_zero_base = if base == GPR::RDX { GPR::RAX } else { GPR::RDX };
  a.emit_mov(
  Size::S64,
  Location::Imm64((&NEG_ZERO as *const u128) as u64),
  - Location::GPR(GPR::RDX),
  + Location::GPR(neg_zero_base),
  );
  a.emit_mov(
  Size::S64,
  - Location::Memory(GPR::RDX, 0),
  + Location::Memory(neg_zero_base, 0),
  Location::Memory(base, disp),
  );
  }
  