On Fri, Oct 11, 2024 at 8:33 PM Hongtao Liu <crazy...@gmail.com> wrote:
>
> On Fri, Oct 11, 2024 at 8:22 PM Richard Biener <rguent...@suse.de> wrote:
> >
> > The following helps the x86 backend by canonicalizing FMAs to have
> > any negation done to one of the commutative multiplication operands
> > be done to a register (and not a memory operand). Likewise to
> > put a register operand first and a memory operand second;
> > swap_commutative_operands_p seems to treat REG_P and MEM_P the
> > same but comments indicate "complex expressiosn should be first".
> >
> > In particular this does (fma MEM REG REG) -> (fma REG MEM REG) and
> > (fma (neg MEM) REG REG) -> (fma (neg REG) MEM REG) which are the
> > reasons for the testsuite regressions in gcc.target/i386/cond_op_fma*.c
> >
> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
> >
> > I'm not quite sure this is the correct approach - simplify-rtx
> > doesn't seem to do "only canonicalization" but the existing FMA
> > case looks odd in that context.
> >
> > Should the target simply reject cases with wrong "canonicalization"
> > or does it need to cope with all variants in the patterns that fail
> > matching during combine without the change?
> Let me try the backend fix first.
The backend fix requires at least 8 more patterns, so I think RTL
canonicalization would be better.
Please go ahead with the patch.
> >
> > Thanks,
> > Richard.
> >
> > PR target/117072
> > * simplify-rtx.cc (simplify_context::simplify_ternary_operation):
> > Adjust FMA canonicalization.
> > ---
> > gcc/simplify-rtx.cc | 15 +++++++++++++--
> > 1 file changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
> > index e8e60404ef6..8b4fa0d7aa4 100644
> > --- a/gcc/simplify-rtx.cc
> > +++ b/gcc/simplify-rtx.cc
> > @@ -6830,10 +6830,21 @@ simplify_context::simplify_ternary_operation
> > (rtx_code code, machine_mode mode,
> > op0 = tem, op1 = XEXP (op1, 0), any_change = true;
> > }
> >
> > - /* Canonicalize the two multiplication operands. */
> > + /* Canonicalize the two multiplication operands. A negation
> > + should go first and if possible the negation should be
> > + to a register. */
> > /* a * -b + c => -b * a + c. */
> > - if (swap_commutative_operands_p (op0, op1))
> > + if (swap_commutative_operands_p (op0, op1)
> > + || (REG_P (op1) && !REG_P (op0) && GET_CODE (op0) != NEG))
> > std::swap (op0, op1), any_change = true;
> > + else if (GET_CODE (op0) == NEG && !REG_P (XEXP (op0, 0))
> > + && REG_P (op1))
> > + {
> > + op0 = XEXP (op0, 0);
> > + op1 = simplify_gen_unary (NEG, mode, op1, mode);
> > + std::swap (op0, op1);
> > + any_change = true;
> > + }
> >
> > if (any_change)
> > return gen_rtx_FMA (mode, op0, op1, op2);
> > --
> > 2.43.0
>
>
>
> --
> BR,
> Hongtao
--
BR,
Hongtao
