Hi,
On Wed, 23 Nov 2016, Segher Boessenkool wrote:
> r242414, for PR77881, introduces some bugs (PR78390, PR78438, PR78477).
> It all has the same root cause: that patch makes combine convert every
> lowpart subreg of a logical shift right to a zero_extract. This cannot
> work at all if it is not a constant shift,
Even with non-constant shifts it remains an extract and make_extraction
does support variable start positions (which is the shift amount), as does
the zero_extract pattern (depending on target of course).
> if (GET_CODE (inner) == LSHIFTRT
> + && CONST_INT_P (XEXP (inner, 1))
> && GET_MODE_SIZE (mode) < GET_MODE_SIZE (GET_MODE (inner))
> && subreg_lowpart_p (x))
> {
> new_rtx = make_compound_operation (XEXP (inner, 0), next_code);
> + int width = GET_MODE_PRECISION (GET_MODE (inner))
GET_MODE (new_rtx), because that's the object you're giving to
make_extraction, not inner (and not XEXP(inner, 0)).
> + - INTVAL (XEXP (inner, 1));
> + if (width > mode_width)
> + width = mode_width;
> new_rtx = make_extraction (mode, new_rtx, 0, XEXP (inner, 1),
> - mode_width, 1, 0, in_code == COMPARE);
> + width, 1, 0, in_code == COMPARE);
> break;
> }
Ciao,
Michael.
