On Mon, May 25, 2026 at 8:45 PM 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)
> 3. ((x & c) == 0) OP (y & c)
Can you leave out 3 for now? We will need to deal with it later I think.
It is needed due to:
```
/* (type)([0,1]@a != 0) -> (type)a
(type)([0,1]@a == 1) -> (type)a
(type)([0,1]@a == 0) -> a ^ 1
(type)([0,1]@a != 1) -> a ^ 1. */
(for eqne (eq ne)
(simplify
(convert (eqne zero_one_valued_p@0 INTEGER_CST@1))
(if ((integer_zerop (@1) || integer_onep (@1)))
(if ((eqne == EQ_EXPR) ^ integer_zerop (@1))
(convert @0)
/* Only do this if the types match as (type)(a == 0) is
canonical form normally, while `a ^ 1` is canonical when
there is no type change. */
(if (types_match (type, TREE_TYPE (@0)))
(bit_xor @0 { build_one_cst (type); } ))))))
```
Which was added by
https://inbox.sourceware.org/gcc-patches/[email protected]/
.
And then we don't support (t1_7 is zero_one_valued_p here):
_1 = t1_7 == 0;
_2 = (int) _1;
Into:
_t = (t1_7^1)
_2 = (int)_t;
As types_match is not true. That was not done .
I didn't realize this came into play for the `&1` part until now :).
You can keep the testcases for the ones which will match 3 but xfail them.
Thanks,
Andrea
>
> for OP in { ==, !=, ^ } and pow2 masks. The third form is required
> because GCC canonicalize: ((x & c) != 0) into (x & c) before this
> rule runs.
>
> Fold these directly into the canonical xor-mask form:
> ((x ^ y) & c) == 0
> ((x ^ y) & c) != 0
>
> Bootstrapped and tested on aarch64-linux-gnu.
>
> Changes since v1:
> * 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 | 38 ++++++++
> .../gcc.dg/tree-ssa/bool-eq-bitxor.c | 39 ++++++++
> .../gcc.dg/tree-ssa/bool-eq-evenness.c | 43 +++++++++
> gcc/testsuite/gcc.dg/tree-ssa/bool-eq-pow2.c | 89 +++++++++++++++++++
> 4 files changed, 209 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 ff13a07ea94..d41a2b2f329 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -1464,6 +1464,44 @@ 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 ocmp (eq ne bit_xor)
> + (for icmp0 (eq eq ne ne)
> + icmp1 (eq ne eq ne)
> + (simplify
> + (ocmp
> + (icmp0 (bit_and @0 integer_pow2p@1) integer_zerop@3)
> + (icmp1 (bit_and @2 @1) @3))
> + (if (types_match (@0, @2))
> + (with {
> + bool innersame
> + = (icmp0 == EQ_EXPR) == (icmp1 == EQ_EXPR);
> + }
> + (if (innersame == (ocmp == EQ_EXPR))
> + (eq (bit_and (bit_xor @0 @2) @1) @3)
> + (ne (bit_and (bit_xor @0 @2) @1) @3)))))
> +
> + /* Canonicalized: ((x & c) == 0) OP (y & c)
> + because ((y & c) != 0) may fold into (y & c). */
> + (simplify
> + (ocmp
> + (convert?@4
> + (icmp0 (bit_and @0 integer_pow2p@1) integer_zerop@3))
> + (convert?@5
> + (bit_and @2 @1)))
> + (if (types_match (@0, @2))
> + (with {
> + bool innersame
> + = (icmp0 == EQ_EXPR) == false;
> + }
> + (if (innersame == (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 00000000000..05cee9696cf
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/bool-eq-bitxor.c
> @@ -0,0 +1,39 @@
> +/* { 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 "& 1" 4 "optimized" } } */
> 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 00000000000..75df70dc6a4
> --- /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 00000000000..109c5f03610
> --- /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" } } */
> --
> 2.34.1
>
