On Mon, May 18, 2026 at 12:11 AM Shivam Gupta <[email protected]> wrote:
>
> This is a follow-up to the -O1 patch for PR112533.
>
> At -O2, GCC lowers (~x & 1) == (~y & 1) via inlining into:
> _14 = ~x;
> _12 = (bool) _14;
> _13 = ~y;
> _9 = (bool) _13;
> _8 = _9 == _12;
>
> The NOT cancellation (~x == ~y -> x == y) is handled by existing
> forwprop rules before this rule fires.
>
> Add match.pd rule for eq and ne:
>
> (T)(x) == (T)(y) -> (T)(x ^ y) == 0
> (T)(x) != (T)(y) -> (T)(x ^ y) != 0
>
> Bootstrapped and regression tested on aarch64-linux-gnu with
> RUNTESTFLAGS="tree-ssa.exp".
>
> Changes since v1:
> * v2: Generalize the match rule to generic narrowing
> integral equality comparisons from bool equality.
>
> PR tree-optimization/112533
>
> gcc/ChangeLog:
> * match.pd: Add generic narrowing eq/ne to XOR-against-zero
> rule for (T)(x) == (T)(y) where precision(T) < precision(x).
>
> gcc/testsuite/ChangeLog:
> * gcc.dg/tree-ssa/narrow-eq-simplify.c: New test covering
> bool parity and short truncation cases.
>
> Signed-off-by: Shivam Gupta <[email protected]>
> ---
> gcc/match.pd | 16 +++++++
> .../gcc.dg/tree-ssa/narrow-eq-simplify.c | 47 +++++++++++++++++++
> 2 files changed, 63 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/narrow-eq-simplify.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index ff13a07ea94..1fcf28044ee 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -2033,6 +2033,22 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> && element_precision (type) <= element_precision (TREE_TYPE (@1)))
> (bit_xor (convert @0) (convert @1))))
>
> +/* For narrowing conversations:
> + (T)(X) == (T)(Y) -> (T)(X ^ Y) == 0
> + (T)(X) != (T)(Y) -> (T)(X ^ Y) != 0 */
> +(for cmp (eq ne)
> + (simplify
> + (cmp (convert@0 @00) (convert@1 @10))
> + (if (INTEGRAL_TYPE_P (type)
> + && INTEGRAL_TYPE_P (TREE_TYPE (@00))
> + && types_match (@00, @10)
> + && types_match (@0, @1)
> + && TYPE_PRECISION (TREE_TYPE (@0))
> + < TYPE_PRECISION (TREE_TYPE (@00)))
> + (with { tree stype = TREE_TYPE (@0); }
> + (cmp (convert:stype (bit_xor @00 @10))
> + { build_zero_cst (stype); })))))
You need to put this with the other ones that are already doing this
pattern; otherwise this and the other ones won't work. Also I don't
think you need to match the types of @0 and @1 here. Also
INTEGRAL_TYPE_P (type) will be true for INTEGRAL_TYPE_P (TREE_TYPE
(@00)).
Also use itype rather than stype. s here usually stands for signed
while i would stand for inner.
Thanks,
Andrea
> +
> /* Convert ~X ^ C to X ^ ~C. */
> (simplify
> (bit_xor (convert? (bit_not @0)) INTEGER_CST@1)
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/narrow-eq-simplify.c
> b/gcc/testsuite/gcc.dg/tree-ssa/narrow-eq-simplify.c
> new file mode 100644
> index 00000000000..8b03954719a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/narrow-eq-simplify.c
> @@ -0,0 +1,47 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +
> +/* Verify the fix for PR112533 at -O2.
> + (~a & 1) == (~a & 1) is lowered via inlining to
> + (bool)(~a) == (bool)(~b), then existing forwprop rules cancel
> + the NOTs giving (bool)(a) == (bool)(b), which this rule
> + simplifies to (bool)(a ^ b) == 0. */
> +
> +typedef unsigned int u32;
> +
> +static _Bool
> +is_even (u32 a)
> +{
> + return a % 2 == 0;
> +}
> +
> +_Bool
> +same_evenness (u32 a, u32 b)
> +{
> + return is_even (a) == is_even (b);
> +}
> +
> +_Bool
> +diff_evenness (u32 a, u32 b)
> +{
> + return is_even (a) != is_even (b);
> +}
> +
> +short
> +eq_short_not (int a, int b)
> +{
> + short sa = ~a;
> + short sb = ~b;
> + return sa == sb;
> +}
> +
> +short
> +ne_short_not (int a, int b)
> +{
> + short sa = ~a;
> + short sb = ~b;
> + return sa != sb;
> +}
> +
> +/* Verify the XOR form is produced. */
> +/* { dg-final { scan-tree-dump-times "\\\^" 4 "optimized" } } */
> --
> 2.34.1
>
