Adam Nemet <adambne...@gmail.com> writes: > > > I think the right fix is to call convert_to_mode or convert_move in the > > > expansion code which ensure the proper truncation. > > > > That would yield correct code, but wouldn't it throw away the fact > > that the high bits are already known to be zero, and yield redundant > > zero-extension on some platforms? I'm guessing that's why the code was > > originally written to call convert_lowpart rather than convert_to_mode. > > convert_to_mode uses gen_lowpart for truncation if TRULY_NOOP_TRUNCATION.
I was concerned about the !TRULY_NOOP_TRUNCATION case; I didn't want to harm someone else's performance to benefit my chip. But, looking around, it looks like (almost?) every chip either #defines TRULY_NOOP_TRUNCATION or wants this fix. So your suggestion sounds good to me, and in any case using straightforward type conversions should surely be the default choice. -Mat
