On Sat, Jul 25, 2026 at 1:46 AM Andrea Pinski
<[email protected]> wrote:
>
> On Tue, Jul 14, 2026 at 4:47 AM Daniel Barboza
> <[email protected]> wrote:
> >
> > Add patterns to handle the case where we're checking if a bit is set and
> > setting it in case it's not. Similar to the work done in PR64567 but in
> > this case the bit is a result of a 1 << val lshift:
> >
> > (A & BIT) EQ 0 ? A | BIT : A , BIT = 1 << val => A | BIT
> > (A & BIT) NE 0 ? A : A | BIT , BIT = 1 << val => A | BIT
> >
> > Following Andrea's suggestion we're also handling the variants that
> > results in just 'A' if we switch the conditionals:
> >
> > (A & BIT) EQ 0 ? A | BIT : A , BIT = 1 << val => A | BIT
> > (A & BIT) NE 0 ? A | BIT : A , BIT = 1 << val => A
> >
> > (A & BIT) NE 0 ? A : A | BIT , BIT = 1 << val => A | BIT
> > (A & BIT) EQ 0 ? A : A | BIT , BIT = 1 << val => A
> >
> > We're also adding cases where a full bitmask is tested, i.e.:
> >
> > (A & MASK) EQ MASK ? A : A | MASK => A | MASK
> > (A & MASK) NE MASK ? A : A | MASK => A
> >
> > (A & MASK) NE MASK ? A | MASK : A => A | MASK
> > (A & MASK) EQ MASK ? A | MASK : A => A
> >
> > Note that for these simplifications we're not limited to a bit/pow2
> > value like the zero comparisons, which don't work with multiple bits
> > because there's no guarantees to preserve the 'non-zero' cases. E.g.:
> > "(A & 0xF) == 0 ? A | 0xF : A" can't be simplified to just "A | 0xF"
> > because there's a whole range of A lower bits (1,2...E) that would be
> > turned to 0xF in the simplification - bits that would be preserved in
> > the original pattern. This is the same scenario discussed before in
> > PR64567.
> >
> > Bootstrapped and regression tested in x86_64, aarch64 and riscv64.
> >
> > PR tree-optimization/124667
> >
> > gcc/ChangeLog:
> >
> > * match.pd(`(A & BIT) EQ|NE 0 ? A | BIT : A`): New
> > pattern.
> > (`(A & BIT) EQ|NE 0 ? A : A | BIT`): New pattern.
> > (`(A & MASK) EQ|NE MASK ? A : A | MASK`): New pattern.
> > (`(A & MASK) EQ|NE MASK ? A | MASK : A`): New pattern.
> > (`A | (((A >> N) & 1) << N)`): New pattern.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.dg/tree-ssa/pr124667-2.c: New test.
> > * gcc.dg/tree-ssa/pr124667.c: New test.
> > ---
> >
> > Changes from v2:
> > - use 'neeq' to reduce the amount of patterns being added
> > - v2 link: https://gcc.gnu.org/pipermail/gcc-patches/2026-July/723485.html
> >
> > gcc/match.pd | 89 +++++++++++++++++
> > gcc/testsuite/gcc.dg/tree-ssa/pr124667-2.c | 67 +++++++++++++
> > gcc/testsuite/gcc.dg/tree-ssa/pr124667.c | 107 +++++++++++++++++++++
> > 3 files changed, 263 insertions(+)
> > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr124667-2.c
> > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr124667.c
> >
> > diff --git a/gcc/match.pd b/gcc/match.pd
> > index a7cec25dbad..797dce54ae3 100644
> > --- a/gcc/match.pd
> > +++ b/gcc/match.pd
> > @@ -6102,6 +6102,95 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> > (if (wi::to_wide (@2) == ~wi::to_wide (@1))
> > @3))
> >
> > +/* PR124667: Similar to PR64567 above but with the bit given
> > + by an (1 << val) lshift. Note that this shift pattern
> > + guarantees that this is a single bit operation.
> > +
> > + The same pattern, if using '!=' instead of '==', will
> > + result in just 'A'.
> > +
> > + (A & (1 << val)) == 0 ? A |= (1 << val) : A => A |= (1 << val)
> > + (A & (1 << val)) != 0 ? A |= (1 << val) : A => A; */
> > +(for neeq (eq ne)
> > + (simplify
> > + (cond
> > + (neeq (bit_and:c @A (lshift@1 integer_onep @2)) integer_zerop)
> > + (bit_ior:c@3 @A @1)
> > + @A)
> > + (if (neeq == EQ_EXPR)
> > + @3
> > + @A))
>
> Use @0 instead of @A.
Note it was probably a mistake to initially only allow numbers,
letters (or words)
can be much more readable than numbers, esp if there are a lot of captures.
>
> > +
> > +/* PR124667: NE variant of the previous match with switched true/false
> > + legs:
> > +
> > + (A & (1 << val)) != 0 ? A : A |= (1 << val) => A |= (1 << val)
> > + (A & (1 << val)) == 0 ? A : A |= (1 << val) => A; */
> > + (simplify
> > + (cond
> > + (neeq (bit_and:c @A (lshift@1 integer_onep @2)) integer_zerop)
> > + @A
> > + (bit_ior:c@3 @A @1))
> > + (if (neeq == NE_EXPR)
> > + @3
> > + @A))
>
> Likewise.
>
> > +
> > +/* PR124667: a bitmask set simplification that is possible as
> > + long as the whole bitmask is being checked. Switching the
> > + comparison from '==' to '!=' results in 'A':
> > +
> > + (A & B) == B ? A : A |= B => A |= B
> > + (A & B) != B ? A : A |= B => A; */
> > + (simplify
> > + (cond
> > + (neeq:c (bit_and @0 @1) @1)
> > + @0
> > + (bit_ior@2 @0 @1))
> > + (if (neeq == EQ_EXPR)
> > + @2
> > + @0))
> > +
> > +/* PR124667: similar from above with true/false legs switched:
> > +
> > + (A & B) != B ? A |= B : A => A | B.
> > + (A & B) == B ? A |= B : A => A; */
> > +(simplify
> > + (cond
> > + (neeq:c (bit_and @0 @1) @1)
> > + (bit_ior@2 @0 @1)
> > + @0)
> > + (if (neeq == NE_EXPR)
> > + @2
> > + @0)))
> > +
> > +/* PR124667: these also reduces to just "A":
> > + ((A >> val) & 1) == 0 ? A : (A | (1 << val))
> > + ((A >> val) & 1) != 0 ? (A | (1 << val)) : A;
> > +
> > + For both cases the zero_one patterns in lines 4860-4890
> > + will turn both into the following 'original':
> > +
> > + intD.7 bitshiftD.4489 = 1 << bitD.4485;
> > + arrD.4488 = arrD.4488 >> bitD.4485 & 1) * bitshiftD.4489 | arrD.4488;
> > +
> > + And it'll appear back in phiopt as:
> > +
> > + _1 = arrD.4482;
> > + _2 = _1 >> bit_7;
> > + _3 = _2 & 1;
> > + _4 = _3 << bit_7;
>
> I think we can convert:
> _2 = _1 >> bit_7;
> _3 = _2 & 1;
> _4 = _3 << bit_7;
> into:
> _t = 1 << bit_7
> _4 = _1 & _t;
> Instead and I think that will do the right thing in general in other cases
> too.
> I think the CST (1) can be of any value too but we can start with 1.
>
> that will combine with:
> > + _6 = _1 | _4;
> Into _4;
>
> > +
> > + I.e. it'll drop the 'mult' and lshift the zero_one result from the
> > + bit check. This is where we can reduce it. */
> > +(simplify
> > + (bit_ior:c
> > + @0
> > + (lshift
> > + (bit_and:c (rshift @0 @1) integer_onep)
> > + @1))
> > + @0)
> > +
> > #if GIMPLE
> > (match (nop_atomic_bit_test_and_p @0 @1 @4)
> > (bit_and (convert?@4 (ATOMIC_FETCH_OR_XOR_N @2 INTEGER_CST@0 @3))
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr124667-2.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/pr124667-2.c
> > new file mode 100644
> > index 00000000000..aa7ac22e07d
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr124667-2.c
> > @@ -0,0 +1,67 @@
> > +/* { dg-additional-options -O2 } */
> > +/* { dg-additional-options -fdump-tree-optimized } */
> > +
> > +int test1 (int n, int bit)
> > +{
> > + int arr[16];
> > + int bitshift = 1 << bit;
> > +
> > + arr[n] = (arr[n] & bitshift) == 0 ? arr[n] : arr[n] | bitshift;
> > +
> > + return arr[n];
> > +}
> > +
> > +int test1_alt (int n, int bit)
> > +{
> > + int arr[16];
> > + int bitshift = 1 << bit;
> > +
> > + arr[n] = (arr[n] & bitshift) != 0 ? arr[n] | bitshift : arr[n];
> > +
> > + return arr[n];
> > +}
> > +
> > +int test2 (int n, int bit)
> > +{
> > + int arr[16];
> > + int bitshift = 1 << bit;
> > +
> > + arr[n] = ((arr[n] >> bit) & 1) == 0 ? arr[n] : arr[n] | bitshift;
> > +
> > + return arr[n];
> > +}
> > +
> > +int test2_alt (int n, int bit)
> > +{
> > + int arr[16];
> > + int bitshift = 1 << bit;
> > +
> > + arr[n] = ((arr[n] >> bit) & 1) != 0 ? arr[n] | bitshift : arr[n];
> > +
> > + return arr[n];
> > +}
> > +
> > +int test3 (int n)
> > +{
> > + int arr[16];
> > + int bits = 0xF;
> > +
> > + arr[n] = (arr[n] & bits) == bits ? arr[n] | bits : arr[n];
> > +
> > + return arr[n];
> > +}
> > +
> > +int test3_alt (int n)
> > +{
> > + int arr[16];
> > + int bits = 0xF;
> > +
> > + arr[n] = (arr[n] & bits) != bits ? arr[n] : arr[n] | bits;
> > +
> > + return arr[n];
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-times " \\| " 0 optimized } } */
> > +/* { dg-final { scan-tree-dump-times " \& " 0 optimized } } */
> > +/* { dg-final { scan-tree-dump-times " << " 0 optimized } } */
> > +/* { dg-final { scan-tree-dump-times " >> " 0 optimized } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr124667.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/pr124667.c
> > new file mode 100644
> > index 00000000000..9bdbe05a00d
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr124667.c
> > @@ -0,0 +1,107 @@
> > +/* { dg-additional-options -O2 } */
> > +/* { dg-additional-options -fdump-tree-optimized } */
> > +
> > +int bitset1 (int n, int bit)
> > +{
> > + int arr[16];
> > + int bitshift = 1 << bit;
> > +
> > + if ((arr[n] & bitshift) == 0)
> > + arr[n] |= bitshift;
> > +
> > + return arr[n];
> > +}
> > +
> > +int bitset1_alt (int n, int bit)
> > +{
> > + int arr[16];
> > + int bitshift = 1 << bit;
> > +
> > + arr[n] = (arr[n] & bitshift) != 0 ? arr[n] : arr[n] | bitshift;
> > +
> > + return arr[n];
> > +}
> > +
> > +int bitset1b (int n, int bit)
> > +{
> > + int arr[16];
> > + int bitshift = 1 << bit;
> > +
> > + if ((bitshift & arr[n]) == 0)
> > + arr[n] |= bitshift;
> > +
> > + return arr[n];
> > +}
> > +
> > +int bitset1b_alt (int n, int bit)
> > +{
> > + int arr[16];
> > + int bitshift = 1 << bit;
> > +
> > + arr[n] = (bitshift & arr[n]) != 0 ? arr[n] : bitshift | arr[n];
> > +
> > + return arr[n];
> > +}
> > +
> > +int bitset2 (int n)
> > +{
> > + int arr[16];
> > + int bits = 0xF;
> > +
> > + if ((arr[n] & bits) != bits)
> > + arr[n] |= bits;
> > +
> > + return arr[n];
> > +}
> > +
> > +int bitset2_alt (int n)
> > +{
> > + int arr[16];
> > + int bits = 0xF;
> > +
> > + arr[n] = (arr[n] & bits) == bits ? arr[n]: arr[n] | bits;
> > +
> > + return arr[n];
> > +}
> > +
> > +int bitset2b (int n)
> > +{
> > + int arr[16];
> > + int bits = 0xF;
> > +
> > + if ((bits & arr[n]) != bits)
> > + arr[n] |= bits;
> > +
> > + return arr[n];
> > +}
> > +
> > +int bitset2b_alt (int n)
> > +{
> > + int arr[16];
> > + int bits = 0xF;
> > +
> > + arr[n] = (bits & arr[n]) == bits ? arr[n]: bits | arr[n];
> > +
> > + return arr[n];
> > +}
> > +
> > +/* A negative test to ensure we're not optimizing something
> > + we shouldn't. */
> > +int bitset_nosimplify (int n)
> > +{
> > + int arr[16];
> > +
> > + int bits = 0xF;
> > +
> > + /* We can't make the bit_ior unconditional here because the
> > + cond matches for multiple values aside from '0xF' in
> > + which the value wouldn't be touched, e.g. for arr[n] = 0x1
> > + "arr[n] & bits" is also non-zero and the value wouldn't be
> > + changed. */
> > + if ((arr[n] & bits) == 0)
> > + arr[n] |= bits;
> > +
> > + return arr[n];
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-times "goto" 2 optimized } } */
> > --
> > 2.43.0
> >
