On Fri, 3 May 2013 12:49:14 +0000, Paulo Matos <pma...@broadcom.com> wrote: > Hello, > > It seems to me there's a bug in > simplify_const_relational_operation:simplify-rtx.c. > If you set STORE_VALUE_FLAG to -1, if you get to > simplify_const_relational_operation > with code: NE, mode: BImode, op0: reg, op1: const_int 0, then you end up in > line > 4717 calling get_mode_bounds. > > get_mode_bounds will unfortunately return min:0, max:-1 for BImode and GCC > proceeds > to compare val which is 0 using: > /* x != y is always true for y out of range. */ > if (val < mmin || val > mmax) > return const_true_rtx; > > This simplifies the comparison to const_true_rtx in the case STORE_FLAG_VALUE > is -1. > This seems flawed. > > Unless there's some background reason for this to happen this seems like a > bug. BImode > is a two value mode: 0 or STORE_FLAG_VALUE (according to trunc_int_to_mode), > therefore > there are really no bounds and these comparisons in > simplify_const_relational_operation > should take special care if dealing with BImode. Also, having max < min is > strange at > best and I can imagine it can result in pretty strange behaviour if a > developer assumes > max >= min, as usual. > > I am interested in comments to this piece of code. I am happy to patch > simplify_const_relational_operation if you agree with what I said. > > Cheers, > > Paulo Matos
I can't comment on the code in question, but the backend for m68k may be affected since it defines STORE_FLAG_VALUE as -1. Do you have a testcase that would cause wrong code, or a patch to cure the issue? I'd be happy to do some testing on m68k-linux. /Mikael
