Hi Richi, on 2020/6/2 下午7:38, Richard Biener wrote: > On Thu, 28 May 2020, Kewen.Lin wrote: > >> Hi, >> >> This is one repost and you can refer to the original series >> via https://gcc.gnu.org/pipermail/gcc-patches/2020-January/538360.html. >> >> As we discussed in the thread >> https://gcc.gnu.org/ml/gcc-patches/2020-01/msg00196.html >> Original: https://gcc.gnu.org/ml/gcc-patches/2020-01/msg00104.html, >> I'm working to teach IVOPTs to consider D-form group access during unrolling. >> The difference on D-form and other forms during unrolling is we can put the >> stride into displacement field to avoid additional step increment. eg: >> >> With X-form (uf step increment): >> ... >> LD A = baseA, X >> LD B = baseB, X >> ST C = baseC, X >> X = X + stride >> LD A = baseA, X >> LD B = baseB, X >> ST C = baseC, X >> X = X + stride >> LD A = baseA, X >> LD B = baseB, X >> ST C = baseC, X >> X = X + stride >> ... >> >> With D-form (one step increment for each base): >> ... >> LD A = baseA, OFF >> LD B = baseB, OFF >> ST C = baseC, OFF >> LD A = baseA, OFF+stride >> LD B = baseB, OFF+stride >> ST C = baseC, OFF+stride >> LD A = baseA, OFF+2*stride >> LD B = baseB, OFF+2*stride >> ST C = baseC, OFF+2*stride >> ... >> baseA += stride * uf >> baseB += stride * uf >> baseC += stride * uf >> >> Imagining that if the loop get unrolled by 8 times, then 3 step updates with >> D-form vs. 8 step updates with X-form. Here we only need to check stride >> meet D-form field requirement, since if OFF doesn't meet, we can construct >> baseA' with baseA + OFF. > > I'd just mention there are other targets that have the choice between > the above forms. Since IVOPTs itself does not perform the unrolling > the IL it produces is the same, correct? > Yes. Before this patch, IVOPTs doesn't consider the unrolling impacts, it only models things based on what it sees. We can assume it thinks later RTL unrolling won't perform.
With this patch, since the IV choice probably changes, the IL can probably change. The typical difference with this patch is: vect__1.7_15 = MEM[symbol: x, index: ivtmp.19_22, offset: 0B]; vs. vect__1.7_15 = MEM[base: _29, offset: 0B]; BR, Kewen > Richard. >
