On Sat, Jun 13, 2026 at 5:00 AM Zhongyao Chen <[email protected]> wrote: > > On Fri, Jun 12, 2026 at 2:49 PM Haochen Jiang <[email protected]> wrote: > > > > On Linux/x86_64, > > > > 9f8409f2e2c28f64bf6a584bc81afcae0f084785 is the first bad commit > > commit 9f8409f2e2c28f64bf6a584bc81afcae0f084785 > > Author: Zhongyao Chen <[email protected]> > > Date: Wed Jun 3 20:44:59 2026 +0800 > > > > vect: Avoid external fallback while operand swap retry is possible > > > > caused > > > > FAIL: g++.dg/vect/slp-pr98855.cc -std=c++26 scan-tree-dump-not slp1 > > "vectorizing stmts using SLP" > > FAIL: g++.dg/vect/slp-pr98855.cc -std=c++26 scan-tree-dump slp1 "not > > vectorized: vectorization is not profitable" > > > > with GCC configured with > > > > ../../gcc/configure > > --prefix=/export/users3/haochenj/src/gcc-bisect/master/master/r17-1485/usr > > --enable-clocale=gnu --with-system-zlib --with-demangler-in-ld > > --with-fpmath=sse --enable-languages=c,c++,fortran --enable-cet > > --without-isl --enable-libmpx x86_64-linux --disable-bootstrap > > > > To reproduce: > > > > $ cd {build_dir}/gcc && make check > > RUNTESTFLAGS="vect.exp=g++.dg/vect/slp-pr98855.cc > > --target_board='unix{-m64\ -march=cascadelake}'" > > > > (Please directly reply to this email for question about this report.) > > (If you met problems with cascadelake related, disabling AVX512F in command > > line might save that.) > > (However, please make sure that there is no potential problems with AVX512.) > > I took a quick look at PR98855. The current FAIL does not look like > the original issue there. > The inner loop is still scalar, and it seems we only vectorize the > final store now. > > So I suspect this is more about cost model, the estimated costs are close. > And I'm not sure which is really better, but from the asm, the scalar > version looks better, since it uses fewer instructions.
One option is to add -mtune=generic to the testcase, since that reflects what it was built for. > > -- > Regards, > Zhongyao
