On Fri, Feb 12, 2016 at 11:23:26AM +0100, Richard Biener wrote:
I am testing the following patch which fixes PR69771 where the code
doesn't match the comment before it. We get to expand a QImode << QImode
shift but the shift amount was of type int and thus it was expanded
as SImode constant. Then
/* In case the insn wants input operands in modes different from
those of the actual operands, convert the operands. It would
seem that we don't need to convert CONST_INTs, but we do, so
that they're properly zero-extended, sign-extended or truncated
for their mode. */
has to apply as we need to re-extend the VOIDmode CONST_INT for
QImode. But then mode1 is computed as 'mode' (QImode) which happens
to match what is expected even though the constant isn't valid.
The fix is IMHO to always call convert_modes for VOIDmode ops
(if the target doesn't expect VOIDmode itself).
Bootstrap and regtest running on x86_64-unknown-linux-gnu, ok for trunk?
This looks like the PR69764 fix I've sent last night (and updated patch
this morning).
BTW, I wouldn't use a runtime test with clearly undefined behavior,
especially not if it tests what the outcome of that UB is.