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
