Richard, please have a look at my question below in a reference to your previous statement.
On Thu, 18 Jun 2015, Steve Ellcey wrote: > OK, I checked in the prequel patch and here is a new copy of the > original patch based off of that (and with no HONOR_NAN checks in the > fma/madd instructions). > > OK for checkin? Please see below for my notes. > 2015-06-18 Steve Ellcey <sell...@imgtec.com> > > * config.gcc (mips*-*-*): Add fused-madd.opt. Please use angle brackets as per <https://www.gnu.org/prep/standards/html_node/Indicating-the-Part-Changed.html>, i.e.: * config.gcc <mips*-*-*>: Add fused-madd.opt. There's no function or similar entity involved here and `mips*-*-*' is a case value like with the C language's `switch' statement where you'd use angle brackets too to refer to individual cases. > (*nmsub4<mode>_fastmath) Update condition. Extraneous space here. > diff --git a/gcc/config/mips/mips.md b/gcc/config/mips/mips.md > index f6912e1..4f5692c 100644 > --- a/gcc/config/mips/mips.md > +++ b/gcc/config/mips/mips.md [...] > +;; fnma is defined in GCC as (fma (neg op1) op2 op3) > +;; (-op1 * op2) + op3 ==> -(op1 * op2) + op3 ==> -((op1 * op2) - op3) > +;; The mips nmsub instructions implement -((op1 * op2) - op3) > +;; This transformation means we may return the wrong signed zero > +;; so we check HONOR_SIGNED_ZEROS. > + > +(define_expand "fnma<mode>4" > + [(set (match_operand:ANYF 0 "register_operand") > + (fma:ANYF (neg:ANYF (match_operand:ANYF 1 "register_operand")) > + (match_operand:ANYF 2 "register_operand") > + (match_operand:ANYF 3 "register_operand")))] > + "(ISA_HAS_FUSED_MADD3 || ISA_HAS_FUSED_MADD4) > + && !HONOR_SIGNED_ZEROS (<MODE>mode)") Have you considered the alternative/complementary approach proposed by Richard here: <http://gcc.gnu.org/ml/gcc-patches/2010-11/msg00680.html>, i.e. to introduce further expanders, e.g.: fmanM4: (neg:M (fma:M OP1 OP2 OP3)) (multiply-add, negated) fmsnM4: (neg:M (fma:M OP1 OP2 (neg:M OP3))) (multiply-subtract, negated) ? These patterns wouldn't need a check for !HONOR_SIGNED_ZEROS as they match the respective hardware instructions in an exact manner. Therefore I think they would be more useful as they would also suit software that claims/requires full IEEE Std 754 compliance. Richard, do you maintain the introduction of these additional operations would be a good idea and one you're willing to support for the purpose of patch acceptance/approval if implemented? > +;; fnms is defined as: (fma (neg op1) op2 (neg op3)) > +;; ((-op1) * op2) - op3 ==> -(op1 * op2) - op3 ==> -((op1 * op2) + op3) > +;; The mips nmadd instructions implement -((op1 * op2) + op3) > +;; This transformation means we may return the wrong signed zero > +;; so we check HONOR_SIGNED_ZEROS. > + > +(define_expand "fnms<mode>4" > + [(set (match_operand:ANYF 0 "register_operand") > + (fma:ANYF > + (neg:ANYF (match_operand:ANYF 1 "register_operand")) > + (match_operand:ANYF 2 "register_operand") > + (neg:ANYF (match_operand:ANYF 3 "register_operand"))))] > + "(ISA_HAS_FUSED_MADD3 || ISA_HAS_FUSED_MADD4) > + && !HONOR_SIGNED_ZEROS (<MODE>mode)") Same observation here. The change looks good to me otherwise. Maciej
