On Tue, May 26, 2026 at 7:48 PM Andrew Pinski
<[email protected]> wrote:
>
> 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.
That is because we should handle it differently and separately as that
only matters with `&1` there.
The pattern there will be something like
(ne zero_one_valued_p@0 (convert? (eq zero_one_valued_p@1 integer_zerop)))
simplified to:
(eq (convert:TREE_TYPE(@1) @0) @1)
With that pattern, this:
t1_5 = a_4(D) & 1;
t2_7 = b_6(D) & 1; // t2_7 is zero_one_valued_p
_1 = t1_5 == 0;
_2 = (int) _1; // _2 is zero_one_valued_p
_3 = (int) t2_7; // _3 is zero_one_valued_p
_8 = _2 != _3;
return _8;
Will gets turned into:
_8 = t2_7 == t1_5
Thanks,
Drea
>
> 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
> >
