https://gcc.gnu.org/g:01d1d20266a4c1f02457dd9df1b25a733d701466
commit r17-2360-g01d1d20266a4c1f02457dd9df1b25a733d701466 Author: Odysseas Georgoudis <[email protected]> Date: Mon Jul 13 10:09:10 2026 -0600 match.pd: Recognize branchless conditional negate [PR113894] This patch teaches match.pd to recognize the branchless conditional negate idiom (x ^ -cmp) + cmp when cmp is known to be zero or one. The expression is folded to a conditional negate form. For the sign-test spelling based on x < 0, the patch exposes ABS_EXPR. PR tree-optimization/113894 gcc/ChangeLog: * match.pd: Add simplifications for branchless conditional negate and sign-test absolute value idioms. gcc/testsuite/ChangeLog: * gcc.dg/tree-ssa/pr113894.c: New test. Diff: --- gcc/match.pd | 17 +++++++++ gcc/testsuite/gcc.dg/tree-ssa/pr113894.c | 63 ++++++++++++++++++++++++++++++++ 2 files changed, 80 insertions(+) diff --git a/gcc/match.pd b/gcc/match.pd index 9d4ab622fe57..d1a12c35ed36 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -236,6 +236,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) && !TYPE_UNSIGNED (TREE_TYPE (@0))) (abs @0))) +/* (X ^ -(X < 0)) + (X < 0) -> abs (X) */ +(simplify + (plus:c (bit_xor:c @0 (negate (convert@1 (lt @0 integer_zerop)))) @1) + (if (INTEGRAL_TYPE_P (TREE_TYPE (@0)) + && !TYPE_UNSIGNED (TREE_TYPE (@0)) + && !TYPE_SATURATING (TREE_TYPE (@0)) + && (GIMPLE || !TREE_SIDE_EFFECTS (@0))) + (abs @0))) + /* Following match patterns are used by the match_spaceship function to detect all possible spaceship combinations. */ #if GIMPLE @@ -4853,6 +4862,14 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) && (GIMPLE || !TREE_SIDE_EFFECTS (@1))) (cond (convert:boolean_type_node @2) @1 @0))) +/* Transform (A ^ -cmp) + cmp into cmp ? -A : A. */ +(simplify + (plus:c (bit_xor:c @0 (negate zero_one_valued_p@1)) @1) + (if (INTEGRAL_TYPE_P (type) + && !TYPE_SATURATING (type) + && (GIMPLE || !TREE_SIDE_EFFECTS (@0))) + (cond (convert:boolean_type_node @1) (negate @0) @0))) + /* Transform A & (B*cmp) into (A&B)*cmp. */ (simplify (bit_and:c (mult:cs zero_one_valued_p@0 @1) @2) diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr113894.c b/gcc/testsuite/gcc.dg/tree-ssa/pr113894.c new file mode 100644 index 000000000000..dc7a450d3e8d --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr113894.c @@ -0,0 +1,63 @@ +/* PR tree-optimization/113894 */ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-forwprop1" } */ + +int f_cmp_lt(int x, int y) +{ + int cmp = x < y; + return (x ^ -cmp) + cmp; +} + +int f_cmp_gt_commuted(int x, int y) +{ + int cmp = x > y; + return cmp + (-cmp ^ x); +} + +unsigned f_unsigned_cmp(unsigned x, unsigned y) +{ + unsigned cmp = x < y; + return (x ^ -cmp) + cmp; +} + +int f_mask(int x, unsigned y) +{ + int cmp = y & 1; + return (x ^ -cmp) + cmp; +} + +int f_bool(int x, _Bool cmp) +{ + int icmp = cmp; + return (x ^ -icmp) + icmp; +} + +int f_abs_int(int x) +{ + int cmp = x < 0; + return (x ^ -cmp) + cmp; +} + +long f_abs_long(long x) +{ + long cmp = x < 0; + return (x ^ -cmp) + cmp; +} + +int f_signed_not_zero_one(int x, int cmp) +{ + return (x ^ -cmp) + cmp; +} + +unsigned f_unsigned_not_zero_one(unsigned x, unsigned cmp) +{ + return (x ^ -cmp) + cmp; +} + +/* The branchless conditional negate spelling should only survive when cmp is + not known to be 0 or 1. */ +/* { dg-final { scan-tree-dump-times " \\^ " 2 "forwprop1" } } */ +/* Sign tests should expose absolute value. */ +/* { dg-final { scan-tree-dump-times " = ABS_EXPR" 2 "forwprop1" } } */ +/* Other zero-one predicates should expose conditional negation. */ +/* { dg-final { scan-tree-dump-times " \\? " 5 "forwprop1" } } */
