Hi! On Mon, Dec 11, 2017 at 02:18:53PM +0000, James Greenhalgh wrote: > > In simplify_set we try transforming the paradoxical subreg expression: > > (set FOO (subreg:M (mem:N BAR) 0)) > > in to: > > (set FOO (zero_extend:M (mem:N BAR))) > > However, this code does not consider the case where M is a vector > mode, allowing it to construct (for example): > > (zero_extend:V4SI (mem:SI)) > > This would clearly have the wrong semantics, but fortunately we fail long > before then in expand_compound_operation. As we really don't want a vector > zero_extend of a scalar value. > > We need to explicitly reject vector modes from this transformation.
It does not consider any other modes either. Both modes involved are required to be SCALAR_INT_MODE_P (for zero_extend to be valid at all and to be equivalent to the subreg); could you test for that instead please? Segher
