Andrew Stubbs <a...@codesourcery.com> writes: > On 06/08/2020 04:54, Richard Sandiford wrote: >>> diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c >>> index f9b0e9714d9..d7067989ad7 100644 >>> --- a/gcc/emit-rtl.c >>> +++ b/gcc/emit-rtl.c >>> @@ -947,6 +947,11 @@ validate_subreg (machine_mode omode, machine_mode >>> imode, >>> else if (VECTOR_MODE_P (omode) >>> && GET_MODE_INNER (omode) == GET_MODE_INNER (imode)) >>> ; >>> + /* Allow sections of vectors, both smaller and paradoxical. (This just >>> + works for integers, but needs to be explicitly allowed for floats.) >>> */ >>> + else if (VECTOR_MODE_P (omode) && VECTOR_MODE_P (imode) >>> + && GET_MODE_INNER (omode) == GET_MODE_INNER (imode)) >>> + ; >> >> Might be missing something, but isn't this a subcondition of the >> previous “else if”? It looks like that ought to catch every case >> that the new one does. > > Apparently, Hongtao and Uroš fixed my problem while I was working on this. > > Yes, my patch does the same (although I would question whether it's safe > to use "GET_MODE_INNER (imode)" without having first confirmed "imode" > is a vector mode).
FWIW, skipping the VECTOR_MODE_P test means that we also allow vector paradoxical subregs of scalars, which can be useful if you're trying to make a vector in which only element 0 is initialised. (Only works for element 0 though.) IIRC this is what some of the x86 patterns do. Guess it means we also allow vector subregs of complex values, but that kind-of seems OK/useful too. Thanks, Richard
