On Tue, Aug 25, 2015 at 11:02 PM, Jeff Law <l...@redhat.com> wrote: > On 08/21/2015 10:30 AM, Ilya Enkovich wrote: >>> >>> If we're checking an optab to drive an optimization, then we're probably >>> on >>> the wrong track. >> >> >> That's totally similar to VEC_COND_EXPR which we generate comparison into. > > It is. The vectorizer is riddled with this stuff. Sigh. So I won't > consider this a negative for the scalar mask support.
Hey, just because it's already bad don't make it worse! >> >>> I think this ties into the overall discussion about >>> whether or not to represent these masks in gimple or try to handle them >>> later during gimple->rtl expansion. >> >> >> Currently we don't have any abstraction for masks, it is supported >> using vector of integers. When I expand it I have no idea whether it >> is just a vector of integers to be stored or a mask to be used for >> MASK_LOAD. Actually it may be used in both cases at the same time. >> >> Handling it in RTL means we have to undo bool->int transformation made >> in GIMPLE. For trivial cases it may be easy but in generic it can be >> challenging. I want to avoid it from the beginning. > > I wasn't suggesting handling them in RTL, but at the border between gimple > and RTL. > > But if we can't reliably determine how a particular mask is going to be used > at that point, then doing things at the gimple/RTL border may be a > spectacularly bad idea ;-) Yeah, I also see Ilyas point here. Basically the new integer masks are generated by if-conversion only. What I was suggesting is to differentiate both cases by making vector comparisons always result in vector<bool>. Thus if you have if (a < b || d > e) x = c; then vectorized if-converted code would generate vector<bool> cnd = a < b; vector<bool> cnd2 = d > e; vector<bool> cnd3 = cnd | cnd2; x = cnd3 ? c : x; when the target supports vector<bool> and otherwise vector<int> cnd = a < b ? -1 : 0; vector<int> cnd2 = d > e ? -1 : 0; vector<int> cnd3 = cnd | cnd2; x = cnd3 ? c : x; which means only VEC_COND expr would support both kind of masks (well, and the IFNs for masked loads/stores). Basically the vectorizer needs to handle vectorizing conditions like cnd = a < b; dependent on target support for masks (that is vectorizing of 'bool' operations). Reworking the existing vectorization of bool operations to not depend on pattern detection would be a first step (and already soving a few PRs on the way). Richard. > > jeff
