[PATCH] Fix PR69771, bogus CONST_INT during shift expansion

Jakub Jelinek jakub@redhat.com
Fri Feb 12 10:32:00 GMT 2016

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.

> 2016-02-12  Richard Biener  <rguenther@suse.de>
> 	PR rtl-optimization/69771
> 	* optabs.c (expand_binop_directly): Properly zero-/sign-extend
> 	VOIDmode operands.
> 	* gcc.dg/torture/pr69771.c: New testcase.


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