Ajit Agarwal <aagar...@linux.ibm.com> writes: > Hello Richard: > > > On 14/02/24 10:45 pm, Richard Sandiford wrote: >> Ajit Agarwal <aagar...@linux.ibm.com> writes: >>>>> diff --git a/gcc/emit-rtl.cc b/gcc/emit-rtl.cc >>>>> index 1856fa4884f..ffc47a6eaa0 100644 >>>>> --- a/gcc/emit-rtl.cc >>>>> +++ b/gcc/emit-rtl.cc >>>>> @@ -921,7 +921,7 @@ validate_subreg (machine_mode omode, machine_mode >>>>> imode, >>>>> return false; >>>>> >>>>> /* The subreg offset cannot be outside the inner object. */ >>>>> - if (maybe_ge (offset, isize)) >>>>> + if (maybe_gt (offset, isize)) >>>>> return false; >>>> >>>> Can you explain why this change is needed? >>>> >>> >>> This is required in rs6000 target where we generate the subreg >>> with offset 16 from OO mode (256 bit) to 128 bit vector modes. >>> Otherwise it segfaults. >> >> Could you go into more detail? Why does that subreg lead to a segfault? >> >> In itself, a 16-byte subreg at byte offset 16 into a 32-byte pair is pretty >> standard. AArch64 uses this too for its vector load/store pairs (and for >> structure pairs more generally). >> > > If we want to create subreg V16QI (reg OO R) 16) imode is V16QI (isize = 16) > and offset > is 16. maybe_ge (offset, isize) return true and validate_subreg returns false;
isize is supposed to be the size of the "inner mode", which in this case is OO. Since OO is a 32-bit mode, I would expect isize to be 32 rather than 16. Is that not the case? Or is the problem that something is trying to take a subreg of a subreg? If so, that is only valid in certain cases. It isn't for example valid to use a subreg operation to move between (subreg:V16QI (reg:OO X) 16) and (subreg:V16QI (reg:OO X) 0). Thanks, Richard
