Re: [PATCH v5] match.pd: Simplify (~A & 1) == (~B & 1) at -O1 [PR112533]

On Sat, Aug 15, 2026 at 8:38 AM Shivam Gupta <[email protected]> wrote:
>
> At -O1, GCC lowers (~a & 1) == (~b & 1) into two different GIMPLE
> forms depending on whether the boolean values come from a function
> return boundary or an inline expression:
>
>   1. Via function return (e.g. inlined is_even), GCC preserves the
>      eq/ne form because the function boundary hides the internal
>      structure from the gimplifier:
>        ((a&1)==0) == ((b&1)==0)   outer node is eq/ne
>
>   2. Via inline expression (directly written), GCC sees the full
>      boolean expression tree at once and folds to bit_xor during
>      gimplification:
>        ((a&1)!=0) ^ ((b&1)==0)   outer node is bit_xor
>
> Add a generalized match.pd rule handling:
>   1. ((x & c) == 0) OP ((y & c) == 0)
>   2. ((x & c) != 0) OP ((y & c) == 0)
>
> for OP in { ==, !=, ^ } and pow2 masks.
>
> Fold these directly into the canonical xor-mask form:
>   ((x ^ y) & c) == 0
>   ((x ^ y) & c) != 0
>
> Bootstrapped and tested on aarch64-linux-gnu with
> RUNTESTFLAGS="tree-ssa.exp".

This looks OK now.  I'll note you're required to run the full testsuite,
not only the tree-ssa.exp part.  I'll do that this time and will push
after that succeeded.

Richard.

> Changes since v1:
> * v5: Add :s to the inner comparisons and bit_and expressions.
>       Simplify the innersame check to compare icmp0 and icmp1
>       directly.
>
> * v4: Removed the ((x & c) == 0) OP (y & c) simplify rule and
>       mark the corresponding test case as XFAIL.
>
> * v3: Collapse both previous simplify rules into one generalized
>       matcher covering all combinations of outer {eq, ne, bit_xor}
>       and inner {eq, ne} comparisons.
>       Add missing mixed-polarity test cases.
>
> * v2: Generalize mask from integer_onep to integer_pow2p.
>       Combine both patterns into single one.
>       Split test into bool-eq-evenness.c, bool-eq-bitxor.c,
>       bool-eq-pow2.c.
>
>         PR tree-optimization/112533
>
> gcc/ChangeLog:
>         * match.pd: Canonicalize boolean comparisons of masked pow2
>         bits into xor-mask tests.
>
> gcc/testsuite/ChangeLog:
>         * gcc.dg/tree-ssa/bool-eq-bitxor.c: New test.
>         * gcc.dg/tree-ssa/bool-eq-evenness.c: New test.
>         * gcc.dg/tree-ssa/bool-eq-pow2.c: New test.
>
> Signed-off-by: Shivam Gupta <[email protected]>
> ---
>  gcc/match.pd                                  | 20 +++++
>  .../gcc.dg/tree-ssa/bool-eq-bitxor.c          | 42 +++++++++
>  .../gcc.dg/tree-ssa/bool-eq-evenness.c        | 43 +++++++++
>  gcc/testsuite/gcc.dg/tree-ssa/bool-eq-pow2.c  | 89 +++++++++++++++++++
>  4 files changed, 194 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/bool-eq-bitxor.c
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/bool-eq-evenness.c
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/bool-eq-pow2.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 02684d8a3..7a052365b 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -1564,6 +1564,26 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>    (if (TYPE_UNSIGNED (type))
>      (bit_and @0 (bit_not (lshift { build_all_ones_cst (type); } @1)))))
>
> +/* PR112533: Canonicalize boolean comparisons of masked pow2 bits into
> +   xor-mask tests.
> +   ((x & c) == 0) == ((y & c) == 0) -> (((x ^ y) & c) == 0)
> +   ((x & c) == 0) != ((y & c) == 0) -> (((x ^ y) & c) != 0)
> +   and equivalent xor forms.  */
> +(for masked_ocmp (eq ne bit_xor)
> + (for icmp0 (eq eq ne ne)
> +      icmp1 (eq ne eq ne)
> +  (simplify
> +   (masked_ocmp
> +    (icmp0:s (bit_and:s @0 integer_pow2p@1) integer_zerop@3)
> +    (icmp1:s (bit_and:s @2 @1) @3))
> +   (if (types_match (@0, @2))
> +    (with {
> +      bool innersame = icmp0 == icmp1;
> +    }
> +     (if (innersame == (masked_ocmp == EQ_EXPR))
> +      (eq (bit_and (bit_xor @0 @2) @1) @3)
> +      (ne (bit_and (bit_xor @0 @2) @1) @3)))))))
> +
>  (for bitop (bit_and bit_ior)
>       cmp (eq ne)
>   /* PR35691: Transform
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/bool-eq-bitxor.c b/gcc/testsuite/gcc.dg/tree-ssa/bool-eq-bitxor.c
> new file mode 100644
> index 000000000..bc263e809
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/bool-eq-bitxor.c
> @@ -0,0 +1,42 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fdump-tree-optimized" } */
> +
> +typedef unsigned int u32;
> +
> +_Bool
> +xor_ne_eq (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 != 0) ^ (t2 == 0);
> +}
> +
> +_Bool
> +xor_eq_eq (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 == 0) ^ (t2 == 0);
> +}
> +
> +_Bool
> +xor_eq_ne (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 == 0) ^ (t2 != 0);
> +}
> +
> +_Bool
> +xor_ne_ne (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 != 0) ^ (t2 != 0);
> +}
> +
> +/* Verify all functions canonicalize to xor-mask tests.  */
> +/* { dg-final { scan-tree-dump-times "a_\[0-9\]+\\(D\\) \\^ b_\[0-9\]+\\(D\\)" 3 "optimized" } } */
> +
> +/* xor_eq_ne not optimized yet due to zero_one_valued_p canonicalization.  */
> +/* { dg-final { scan-tree-dump-times "& 1" 2 "optimized" { xfail *-*-* } } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/bool-eq-evenness.c b/gcc/testsuite/gcc.dg/tree-ssa/bool-eq-evenness.c
> new file mode 100644
> index 000000000..75df70dc6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/bool-eq-evenness.c
> @@ -0,0 +1,43 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fdump-tree-optimized" } */
> +
> +/* Verify the GIMPLE-level fix for PR112533. */
> +
> +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);
> +}
> +
> +_Bool
> +same_evenness_cmp_zero (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 == 0) == (t2 == 0);
> +}
> +
> +_Bool
> +diff_evenness_cmp_zero (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 == 0) != (t2 == 0);
> +}
> +
> +/* Verify all functions canonicalize to xor forms.  */
> +/* { dg-final { scan-tree-dump-times "\\^" 4 "optimized" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/bool-eq-pow2.c b/gcc/testsuite/gcc.dg/tree-ssa/bool-eq-pow2.c
> new file mode 100644
> index 000000000..109c5f036
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/bool-eq-pow2.c
> @@ -0,0 +1,89 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fdump-tree-optimized" } */
> +
> +typedef unsigned int u32;
> +
> +_Bool
> +eq_eq_outer_eq_mask2 (u32 a, u32 b)
> +{
> +  u32 t1 = a & 2;
> +  u32 t2 = b & 2;
> +  return (t1 == 0) == (t2 == 0);
> +}
> +
> +_Bool
> +eq_eq_outer_eq_mask4 (u32 a, u32 b)
> +{
> +  u32 t1 = a & 4;
> +  u32 t2 = b & 4;
> +  return (t1 == 0) == (t2 == 0);
> +}
> +
> +_Bool
> +eq_eq_outer_ne (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 == 0) != (t2 == 0);
> +}
> +
> +_Bool
> +ne_eq_outer_eq (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 != 0) == (t2 == 0);
> +}
> +
> +_Bool
> +ne_eq_outer_ne (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 != 0) != (t2 == 0);
> +}
> +
> +_Bool
> +eq_ne_outer_eq (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 == 0) == (t2 != 0);
> +}
> +
> +_Bool
> +eq_ne_outer_ne (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 == 0) != (t2 != 0);
> +}
> +
> +_Bool
> +ne_ne_outer_eq (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 != 0) == (t2 != 0);
> +}
> +
> +_Bool
> +ne_ne_outer_ne (u32 a, u32 b)
> +{
> +  u32 t1 = a & 1;
> +  u32 t2 = b & 1;
> +  return (t1 != 0) != (t2 != 0);
> +}
> +
> +/* Non-power-of-2: should not be simplified.  */
> +_Bool
> +eq_eq_outer_eq_nonpow2 (u32 a, u32 b)
> +{
> +  u32 t1 = a & 3;
> +  u32 t2 = b & 3;
> +  return (t1 == 0) == (t2 == 0);
> +}
> +
> +/* Verify power-of-2 masks are simplified, non-power-of-2 masks are not.  */
> +/* { dg-final { scan-tree-dump-times "a_\[0-9\]+\\(D\\) \\^ b_\[0-9\]+\\(D\\)" 9 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times "& 3" 2 "optimized" } } */
> --
> 2.43.0
>