On Fri, Feb 12, 2016 at 01:48:36PM +0100, Richard Biener wrote:
> But my patch should deal with all this.
>
> - mode1 = GET_MODE (xop1) != VOIDmode ? GET_MODE (xop1) : mode;
> - if (xmode1 != VOIDmode && xmode1 != mode1)
> + mode1 = GET_MODE (xop1);
> + if (xmode1 != mode1)
> {
> xop1 = convert_modes (xmode1, mode1, xop1, unsignedp);
> mode1 = xmode1;
>
> so if xop1 is not VOIDmode and already of xmode1 we won't do anything.
> But if it is VOIDmode (and xmode1 is not VOIDmode) we'll always
> do convert_modes.
The case I'm worried about is if xop1 is a constant in narrower
mode (let's say QImode), e.g. -15, unsignedp is 1, and xmode1 is
wider. Then previously we'd zero extend it, thus get
0xf1, but with your patch we'll end up with -15 instead,
because convert_modes will be called e.g. with (SImode, VOIDmode, xop1, 1)
instead of (SImode, QImode, xop1, 1).
Dunno if it is just hypothetical or real.
Jakub
