On Fri, Aug 16, 2024 at 4:24 PM Konstantinos Eleftheriou
<konstantinos.elefther...@vrull.eu> wrote:
>
> From: kelefth <konstantinos.elefther...@vrull.eu>
>
> In expressions like (a != b || ((a ^ b) & CST0) == CST1) and
> (a != b || (a ^ b) == CST), (a ^ b) is folded to false.
> In the equivalent expressions (((a ^ b) & CST0) == CST1 || a != b) and
> ((a ^ b) == CST, (a ^ b) || a != b) this is not happening.
>
> This patch adds the following simplifications in match.pd:
> ((a ^ b) & CST0) == CST1 || a != b --> 0 == (CST1 || a != b)
> (a ^ b) == CST || a != b --> 0 == CST || (a != b)
>
> PR tree-optimization/114326
>
> gcc/ChangeLog:
>
> * match.pd: Add two patterns to fold a ^ b to 0, when a == b.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/fold-xor-and-or-1.c: New test.
> * gcc.dg/tree-ssa/fold-xor-and-or-2.c: New test.
> * gcc.dg/tree-ssa/fold-xor-or-1.c: New test.
> * gcc.dg/tree-ssa/fold-xor-or-2.c: New test.
>
> Reviewed-by: Christoph Müllner <christoph.muell...@vrull.eu>
> Signed-off-by: Philipp Tomsich <philipp.toms...@vrull.eu>
> Signed-off-by: Konstantinos Eleftheriou <konstantinos.elefther...@vrull.eu>
> ---
> gcc/match.pd | 30 +++++++++++++++++++
> .../gcc.dg/tree-ssa/fold-xor-and-or-1.c | 17 +++++++++++
> .../gcc.dg/tree-ssa/fold-xor-and-or-2.c | 19 ++++++++++++
> gcc/testsuite/gcc.dg/tree-ssa/fold-xor-or-1.c | 17 +++++++++++
> gcc/testsuite/gcc.dg/tree-ssa/fold-xor-or-2.c | 19 ++++++++++++
> 5 files changed, 102 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/fold-xor-and-or-1.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/fold-xor-and-or-2.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/fold-xor-or-1.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/fold-xor-or-2.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index c9c8478d286..1c55bd72f09 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -10680,3 +10680,33 @@ and,
> }
> (if (full_perm_p)
> (vec_perm (op@3 @0 @1) @3 @2))))))
> +
> +/* ((a ^ b) & CST0) == CST1 || a != b --> 0 == (CST1 || a != b). */
So for CST0 == 0 we don't know nothing - you do not verify
this but this might be a reason to force CST0 to be a constant
(CST1 need not be?). CST0 could be a non-constant as well
if you use tree_expr_nonzero_p on it, right?
> +(for cmp (simple_comparison)
> + (simplify
> + (bit_ior
> + (cmp
> + (bit_and
> + (bit_xor @0 @1)
> + INTEGER_CST)
> + @3)
> + (ne@4 @0 @1))
> + (bit_ior
> + (cmp
> + { build_zero_cst (TREE_TYPE (@0)); }
> + @3)
> + @4)))
> +
> +/* (a ^ b) == CST || a != b --> 0 == CST || (a != b). */
> +(for cmp (simple_comparison)
> + (simplify
> + (bit_ior
> + (cmp
> + (bit_xor @0 @1)
> + @2)
Should this be INTEGER_CST@2? I don't see the comments why CSTs should
be constant and not arbitrary other values?
> + (ne@3 @0 @1))
> + (bit_ior
> + (cmp
> + {build_zero_cst (TREE_TYPE (@0)); }
> + @2)
if @2 is INTEGER_CST you could also statically decide whether it's zero.
I do wonder why we don't (don't we?) simplify (a ^ b) == 0 to a == b?
Likewise for (a ^ b) != 0.
But as said, mentioning 'CST' is probably misleading?
> + @3)))
> \ No newline at end of file
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-and-or-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-and-or-1.c
> new file mode 100644
> index 00000000000..0e6fc1d5515
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-and-or-1.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -fdump-tree-optimized" } */
> +
> +int cmp1(int d1, int d2) {
> + if (((d1 ^ d2) & 0xabcd) == 0 || d1 != d2)
> + return 0;
> + return 1;
> +}
> +
> +int cmp2(int d1, int d2) {
> + if (d1 != d2 || ((d1 ^ d2) & 0xabcd) == 0)
> + return 0;
> + return 1;
> +}
> +
> +/* The if should be removed, so the condition should not exist */
> +/* { dg-final { scan-tree-dump-not "d1_\[0-9\]+.D. \\^ d2_\[0-9\]+.D."
> "optimized" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-and-or-2.c
> b/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-and-or-2.c
> new file mode 100644
> index 00000000000..3f8da111354
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-and-or-2.c
> @@ -0,0 +1,19 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -fdump-tree-optimized" } */
> +
> +typedef unsigned long int uint64_t;
> +
> +int cmp1(uint64_t d1, uint64_t d2) {
> + if (((d1 ^ d2) & 0xabcd) == 0 || d1 != d2)
> + return 0;
> + return 1;
> +}
> +
> +int cmp2(uint64_t d1, uint64_t d2) {
> + if (d1 != d2 || ((d1 ^ d2) & 0xabcd) == 0)
> + return 0;
> + return 1;
> +}
> +
> +/* The if should be removed, so the condition should not exist */
> +/* { dg-final { scan-tree-dump-not "d1_\[0-9\]+.D. \\^ d2_\[0-9\]+.D."
> "optimized" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-or-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-or-1.c
> new file mode 100644
> index 00000000000..0bc849a2d74
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-or-1.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -fdump-tree-optimized" } */
> +
> +int cmp1(int d1, int d2) {
> + if ((d1 ^ d2) == 0xabcd || d1 != d2)
> + return 0;
> + return 1;
> +}
> +
> +int cmp2(int d1, int d2) {
> + if (d1 != d2 || (d1 ^ d2) == 0xabcd)
> + return 0;
> + return 1;
> +}
> +
> +/* The if should be removed, so the condition should not exist */
> +/* { dg-final { scan-tree-dump-not "d1_\[0-9\]+.D. \\^ d2_\[0-9\]+.D."
> "optimized" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-or-2.c
> b/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-or-2.c
> new file mode 100644
> index 00000000000..2276fc1c2ba
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/fold-xor-or-2.c
> @@ -0,0 +1,19 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -fdump-tree-optimized" } */
> +
> +typedef unsigned long int uint64_t;
> +
> +int cmp1(uint64_t d1, uint64_t d2) {
> + if ((d1 ^ d2) == 0xabcd || d1 != d2)
> + return 0;
> + return 1;
> +}
> +
> +int cmp2(uint64_t d1, uint64_t d2) {
> + if (d1 != d2 || (d1 ^ d2) == 0xabcd)
> + return 0;
> + return 1;
> +}
> +
> +/* The if should be removed, so the condition should not exist */
> +/* { dg-final { scan-tree-dump-not "d1_\[0-9\]+.D. \\^ d2_\[0-9\]+.D."
> "optimized" } } */
> --
> 2.46.0
>
