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))
+
+/* 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))
+
+/* 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;
+ _6 = _1 | _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
