On Wed, 13 Jan 2021, Jakub Jelinek wrote:
> Hi!
>
> These simplifications are only simplifications if the (~D ^ C) or (D ^ C)
> expressions fold into constants, but in that case they decrease number of
> operations by 1.
>
> For the first transformation I guess I should add reverse simplification
> when C and D are arbitrary (constants would fold before;
> to be tried incrementally).
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2021-01-13 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/96691
> * match.pd ((~X | C) ^ D -> (X | C) ^ (~D ^ C),
> (~X & C) ^ D -> (X & C) ^ (D ^ C)): New simplifications for constant
> C and D.
>
> * gcc.dg/tree-ssa/pr96691.c: New test.
>
> --- gcc/match.pd.jj 2021-01-12 13:17:35.000000000 +0100
> +++ gcc/match.pd 2021-01-12 21:39:51.310921835 +0100
> @@ -947,6 +947,20 @@ (define_operator_list COND_TERNARY
> (bit_ior:c (bit_xor:c@3 @0 @1) (bit_xor:c (bit_xor:c @1 @2) @0))
> (bit_ior @3 @2))
>
> +/* (~X | C) ^ D -> (X | C) ^ (~D ^ C) if C and D are constants. */
> +(simplify
> + (bit_xor (bit_ior:s (bit_not @0) @1) @2)
> + (if ((TREE_CODE (@1) == INTEGER_CST || TREE_CODE (@1) == VECTOR_CST)
> + && TREE_CODE (@1) == TREE_CODE (@2))
> + (bit_xor (bit_ior @0 @1) (bit_xor (bit_not @2) @1))))
I guess you could use
(bit_xor (bit_ior @0 @1) (bit_xor! (bit_not! @2) @1))
and relax the constant test. Not sure in which circumstances
(bit_xor (bit_not @2) @1) would simplify down to a singleton
(within VN it might CSE for example). Maybe
global1 = (~D) ^ C;
global2 = (~X | C) ^ D;
which VN should then simplify to
global1 = (~D) ^ C;
global2 = (X | C) ^ global1;
of course such case may apply to many more patterns so not sure
if we should start to use ! more aggressively now (it's relatively new).
And yes, the reverse transform would be a simplification in general.
Richard.
> +
> +/* (~X & C) ^ D -> (X & C) ^ (D ^ C) if C and D are constants. */
> +(simplify
> + (bit_xor (bit_and:s (bit_not @0) @1) @2)
> + (if ((TREE_CODE (@1) == INTEGER_CST || TREE_CODE (@1) == VECTOR_CST)
> + && TREE_CODE (@1) == TREE_CODE (@2))
> + (bit_xor (bit_and @0 @1) (bit_xor @2 @1))))
> +
> /* Simplify (~X & Y) to X ^ Y if we know that (X & ~Y) is 0. */
> #if GIMPLE
> (simplify
> --- gcc/testsuite/gcc.dg/tree-ssa/pr96691.c.jj 2021-01-12
> 21:48:35.763025413 +0100
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr96691.c 2021-01-12 21:48:19.579207370
> +0100
> @@ -0,0 +1,21 @@
> +/* PR tree-optimization/96691 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-final { scan-tree-dump-times " \\\| 123;" 1 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " \\\& 123;" 1 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " \\\^ -315;" 1 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " \\\^ 314;" 1 "optimized" } } */
> +/* { dg-final { scan-tree-dump-not " \\\^ 321;" "optimized" } } */
> +/* { dg-final { scan-tree-dump-not " = ~" "optimized" } } */
> +
> +int
> +foo (int x)
> +{
> + return (~x | 123) ^ 321;
> +}
> +
> +int
> +bar (int x)
> +{
> + return (~x & 123) ^ 321;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
