On April 1, 2016 5:18:10 PM GMT+02:00, Segher Boessenkool <seg...@kernel.crashing.org> wrote: >On Fri, Apr 01, 2016 at 09:36:49AM +0200, Richard Biener wrote: >> On Fri, Apr 1, 2016 at 6:54 AM, Segher Boessenkool >> <seg...@kernel.crashing.org> wrote: >> > Sometimes people write loops that they do not want optimized away, >even >> > when the compiler can replace those loops by a simple expression >(or >> > nothing). For such people, this patch adds a compiler option. >> > >> > Bootstrapped on powerpc64-linux; regression check still in progress >> > (with Init(1) to actually test anything). >> >> -fno-tree-scev-cprop? -O0? > >There are other cases where GCC can delete loops, for example cddce1. > >> A new compiler option for this is complete overkill (and it's >implementation >> is gross ;)). Semantics are also unclear, your patch would only make >sure >> to preserve an empty loop with the asm in the latch, it wouldn't >disallow >> replacing the overall effect with a computation. > >That's right, and the loop can even still be unrolled, even fully >unrolled (which is good, not only should we not desert the loop but >we also shouldn't run around so much). > >> Your patch would also miss a few testcases. > >It already makes ~2000 (mainly vectorisation) testcases fail, is that >not enough coverage? :-)
For an April 1st joke yes, otherwise no :) Richard. >Cheers, > > >Segher
