On Wed, Jul 28, 2021 at 2:45 PM Roger Sayle <ro...@nextmovesoftware.com> wrote:
>
>
> Hi Marc,
>
> Thanks for the feedback. After some quality time in gdb, I now appreciate
> that
> match.pd behaves (subtly) differently between generic and gimple, and the
> trees actually being passed to tree_nonzero_bits were not quite what I had
> expected. Sorry for my confusion, the revised patch below is now much
> shorter
> (and my follow-up patch that was originally to tree_nonzero_bits looks like
> it
> now needs to be to get_nonzero_bits!).
>
> This revised patch has been retested on 864_64-pc-linux-gnu with a
> "make bootstrap" and "make -k check" with no new failures.
>
> Ok for mainline?
OK I think. It would be nice if (match ...) could be used to merge
the cases, like
(match (mult_by_constant @0 @1)
(mult @0 INTEGER_CST@1))
(match (mult_by_constant @0 (lshift { integer_one_node; } @1))
(lshift @0 @1)
(match (mult_by_constant @0 integer_one_node)
@0)
but (match ...) can't "mutate" the matching operands, so
at least the shift variant cannot be expressed right now,
likewise the "constant" matching operand doesn't parse.
Richard.
> 2021-07-28 Roger Sayle <ro...@nextmovesoftware.com>
> Marc Glisse <marc.gli...@inria.fr>
>
> gcc/ChangeLog
> * match.pd (bit_ior, bit_xor): Canonicalize (X*C1)|(X*C2) and
> (X*C1)^(X*C2) as X*(C1+C2), and related variants, using
> tree_nonzero_bits to ensure that operands are bit-wise disjoint.
>
> gcc/testsuite/ChangeLog
> * gcc.dg/fold-ior-4.c: New test.
>
> Roger
> --
>
> -----Original Message-----
> From: Marc Glisse <marc.gli...@inria.fr>
> Sent: 26 July 2021 16:45
> To: Roger Sayle <ro...@nextmovesoftware.com>
> Cc: 'GCC Patches' <gcc-patches@gcc.gnu.org>
> Subject: Re: [PATCH] Fold (X<<C1)^(X<<C2) to a multiplication when possible.
>
> On Mon, 26 Jul 2021, Roger Sayle wrote:
>
> > The one aspect that's a little odd is that each transform is paired
> > with a convert@1 variant, using the efficient match machinery to
> > expose any zero extension to fold-const.c's tree_nonzero_bits
> functionality.
>
> Copying the first transform for context
>
> +(for op (bit_ior bit_xor)
> + (simplify
> + (op (mult:s@0 @1 INTEGER_CST@2)
> + (mult:s@3 @1 INTEGER_CST@4))
> + (if (INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_WRAPS (type)
> + && (tree_nonzero_bits (@0) & tree_nonzero_bits (@3)) == 0)
> + (mult @1
> + { wide_int_to_tree (type, wi::to_wide (@2) + wi::to_wide (@4));
> })))
> +(simplify
> + (op (mult:s@0 (convert@1 @2) INTEGER_CST@3)
> + (mult:s@4 (convert@1 @2) INTEGER_CST@5))
> + (if (INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_WRAPS (type)
> + && (tree_nonzero_bits (@0) & tree_nonzero_bits (@4)) == 0)
> + (mult @1
> + { wide_int_to_tree (type, wi::to_wide (@3) + wi::to_wide (@5));
> })))
>
> Could you explain how the convert helps exactly?
>
> --
> Marc Glisse
