https://gcc.gnu.org/g:75f572322c011229794476502f52a9ae530107f8
commit r17-3225-g75f572322c011229794476502f52a9ae530107f8 Author: Kyrylo Tkachov <[email protected]> Date: Mon Aug 10 20:39:14 2026 +0200 match.pd: fold a round up spelled with inclusive or Linux spells a power-of-two round up as: ((x - 1) | (2^k - 1)) + 1 For wrapping arithmetic, this is: (x + (2^k - 1)) & -(2^k) The latter form needs one fewer operation and exposes the zero low bits. Apply the identity to scalar and vector integral types. Use :s on the inclusive-or expression so the fold does not add work when that value remains live. unsigned long round_up (unsigned long x) { return ((x - 1) | 4095) + 1; } aarch64 -O2: before: round_up: sub x0, x0, #1 orr x0, x0, 4095 add x0, x0, 1 ret after: round_up: add x0, x0, 4095 and x0, x0, -4096 ret Bootstrapped and tested on aarch64-none-linux-gnu. gcc/ChangeLog: * match.pd (((X - 1) | C) + 1): New simplification. gcc/testsuite/ChangeLog: * gcc.dg/tree-ssa/round-up-ior-1.c: New test. * gcc.dg/tree-ssa/round-up-ior-2.c: Likewise. Signed-off-by: Kyrylo Tkachov <[email protected]> Diff: --- gcc/match.pd | 17 +++++++++++++ gcc/testsuite/gcc.dg/tree-ssa/round-up-ior-1.c | 34 ++++++++++++++++++++++++++ gcc/testsuite/gcc.dg/tree-ssa/round-up-ior-2.c | 10 ++++++++ 3 files changed, 61 insertions(+) diff --git a/gcc/match.pd b/gcc/match.pd index beea45357e22..eee44365ea37 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -2072,6 +2072,23 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) (bit_and (plus @0 @1) { build_uniform_cst (type, wide_int_to_tree (etype, wi::bit_not (c))); })))) + +/* ((X - 1) | C) + 1 -> (X + C) & ~C, for C a low mask 2^k - 1. + Both forms round X up to a multiple of 2^k. */ +(simplify + (plus (bit_ior:s (plus @0 integer_minus_onep) + uniform_integer_cst_p@1) + integer_onep) + (with { tree cst = uniform_integer_cst_p (@1); + tree etype = TREE_TYPE (cst); + wide_int c = wi::to_wide (cst); } + (if (TYPE_OVERFLOW_WRAPS (type) + && c != 0 + && wi::popcount (c + 1) == 1) + (bit_and (plus @0 @1) + { build_uniform_cst + (type, wide_int_to_tree (etype, wi::bit_not (c))); })))) + /* (x + y) - min (x, y) -> max (x, y) (x + y) - max (x, y) -> min (x, y) The sum of the minimum and the maximum is the sum of the operands. */ diff --git a/gcc/testsuite/gcc.dg/tree-ssa/round-up-ior-1.c b/gcc/testsuite/gcc.dg/tree-ssa/round-up-ior-1.c new file mode 100644 index 000000000000..991a429742c4 --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/round-up-ior-1.c @@ -0,0 +1,34 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ + +typedef unsigned int v4ui __attribute__ ((vector_size (16))); + +unsigned long +round_up (unsigned long x) +{ + return ((x - 1) | 4095) + 1; +} + +unsigned long +round_up_pages (unsigned long x) +{ + return (((x - 1) | 4095) + 1) >> 12; +} + +v4ui +round_up_vec (v4ui x) +{ + v4ui one = { 1, 1, 1, 1 }; + v4ui mask = { 15, 15, 15, 15 }; + return ((x - one) | mask) + one; +} + +unsigned long +keep (unsigned long x) +{ + return ((x - 1) | 4096) + 1; +} + +/* { dg-final { scan-tree-dump-not "\\| 4095" "optimized" } } */ +/* { dg-final { scan-tree-dump-not "\\|.*15" "optimized" } } */ +/* { dg-final { scan-tree-dump-times "\\| 4096" 1 "optimized" } } */ diff --git a/gcc/testsuite/gcc.dg/tree-ssa/round-up-ior-2.c b/gcc/testsuite/gcc.dg/tree-ssa/round-up-ior-2.c new file mode 100644 index 000000000000..014aeed4c613 --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/round-up-ior-2.c @@ -0,0 +1,10 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fwrapv -fdump-tree-optimized" } */ + +int +round_up (int x) +{ + return ((x - 1) | 15) + 1; +} + +/* { dg-final { scan-tree-dump-not " \\| " "optimized" } } */
