On Thu, May 5, 2022 at 10:30 AM Kewen.Lin <li...@linux.ibm.com> wrote: > > on 2022/5/5 16:09, Richard Biener via Gcc-patches wrote: > > On Thu, May 5, 2022 at 10:07 AM HAO CHEN GUI via Gcc-patches > > <gcc-patches@gcc.gnu.org> wrote: > >> > >> Hi, > >> This patch skips constant folding for fmin/max when either argument > >> is sNaN. According to C standard, > >> fmin(sNaN, sNaN）= qNaN, fmin(sNaN, NaN) = qNaN > >> So signaling NaN should be tested and skipped for fmin/max in match.pd. > >> > >> Bootstrapped and tested on ppc64 Linux BE and LE with no regressions. > >> Is this okay for trunk? Any recommendations? Thanks a lot. > > > > OK. > > > > Thanks, > > Richard. > > > >> ChangeLog > >> > >> 2022-05-05 Haochen Gui <guih...@linux.ibm.com> > >> > >> gcc/ > >> PR target/105414 > >> * match.pd (minmax): Skip constant folding for fmin/fmax when both > >> arguments are sNaN or one is sNaN and another is NaN. > >> > >> gcc/testsuite/ > >> PR target/105414 > >> * gcc.dg/pr105414.c: New. > >> > >> patch.diff > >> > >> diff --git a/gcc/match.pd b/gcc/match.pd > >> index cad61848daa..f256bcbb483 100644 > >> --- a/gcc/match.pd > >> +++ b/gcc/match.pd > >> @@ -3093,7 +3093,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) > >> (for minmax (min max FMIN_ALL FMAX_ALL) > >> (simplify > >> (minmax @0 @0) > >> - @0)) > >> + /* if both are sNaN, it should return qNaN. */ > >> + (if (!tree_expr_maybe_signaling_nan_p (@0)) > >> + @0))) > > Sorry for chiming in. > > IIUC this patch is mainly for libc function fmin/fmax and the iterator here > covers min/max and fmin/fmax. I wonder if it's intent to make this change > for min/max as well? > > As tree.def, "if either operand is NaN, then it is unspecified", the > optimization > for min/max seems still acceptable?
MIN/MAX_EXPR shouldn't even appear with -fsignalling-nans for this reason, at least that's what I thought. But yes, you might have a point here (but maybe it's also not strictly enough specified). One option would be to do (minmax == MAX_EXPR || minmax == MIN_EXPR || !tree_expr ...) Joseph - are MIN_EXPR and MAX_EXPR supposed to turn sNaN into qNaN and the 'undefinedness' is merely as to which operand is chosen? Richard. > > BR, > Kewen
