On Mon, 17 Aug 2026 at 6:36 PM, Richard Biener <[email protected]> wrote:
> 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. > Thanks a lot! Shivam. > > 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 > > >
