> Am 11.08.2026 um 17:00 schrieb Andrea Pinski <[email protected]>:
>
> 3 recent match patterns were added that introduce signed integer overflow
> where
> there was none before. These 3 were in the form of `cmp + (-cmp ^ x)` and
> `((dec_exp + -cmp) ^ -cmp)` In the first 2, ABSU is needed to be used
> and in the other one we need to cast first to the unsigned type before
> taking the 2comps negative value and then cast back.
>
> Bootstrapped and tested on x86_64-linux-gnu.
>
> PR tree-optimization/126418
>
> gcc/ChangeLog:
>
> * match.pd (`((x - (x<0)) ^ -(x<0)`): Use ABSU.
> (`(X ^ -(X < 0)) + (X < 0)`): Likewise.
> (`(A ^ -cmp) + cmp`): Cast to unsigned type
> before taking the negative.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/pr113894.c: Update testcase for ABSU.
> * gcc.dg/tree-ssa/pr123514.c: Likewise.
> * gcc.dg/tree-ssa/pr126418-1.c: New test.
>
> Signed-off-by: Andrea Pinski <[email protected]>
> ---
> gcc/match.pd | 18 +++++++++++++-----
> gcc/testsuite/gcc.dg/tree-ssa/pr113894.c | 2 +-
> gcc/testsuite/gcc.dg/tree-ssa/pr123514.c | 2 +-
> gcc/testsuite/gcc.dg/tree-ssa/pr126418-1.c | 11 +++++++++++
> 4 files changed, 26 insertions(+), 7 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr126418-1.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 50e73177022..751f5571183 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -228,22 +228,24 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> (abs @0)))
> #endif
>
> -/* (X - (X < 0)) ^ -(X < 0) -> abs (X) */
> +/* (X - (X < 0)) ^ -(X < 0) -> absu (X) */
But if X is INT_MIN then we subtract 1 already?
> (simplify
> (bit_xor:c (minus @0 (convert@1 (lt @0 integer_zerop)))
> (negate @1))
> (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
> && !TYPE_UNSIGNED (TREE_TYPE (@0)))
> - (abs @0)))
> + (with { tree utype = unsigned_type_for (type); }
> + (convert (absu:utype @0)))))
>
> -/* (X ^ -(X < 0)) + (X < 0) -> abs (X) */
> +/* (X ^ -(X < 0)) + (X < 0) -> absu (X) */
Likewise
> (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)))
> + (with { tree utype = unsigned_type_for (type); }
> + (convert (absu:utype @0)))))
>
> /* Following match patterns are used by the match_spaceship function to detect
> all possible spaceship combinations. */
> @@ -4960,7 +4962,13 @@
Not enough context here
> DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> (if (INTEGRAL_TYPE_P (type)
> && !TYPE_SATURATING (type)
> && (GIMPLE || !TREE_SIDE_EFFECTS (@0)))
> - (cond (convert:boolean_type_node @1) (negate @0) @0)))
> + /* Do the negate in unsigned type always; otherwise
> + we would be introducing an overflow. */
> + (with { tree utype = unsigned_type_for (type); }
> + (cond
> + (convert:boolean_type_node @1)
> + (convert:type (negate (convert:utype @0)))
> + @0))))
>
> /* Transform A & (B*cmp) into (A&B)*cmp. */
> (simplify
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr113894.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr113894.c
> index dc7a450d3e8..829a214632d 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/pr113894.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr113894.c
> @@ -58,6 +58,6 @@ unsigned f_unsigned_not_zero_one(unsigned x, unsigned cmp)
> 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" } } */
> +/* { dg-final { scan-tree-dump-times " = ABSU_EXPR" 2 "forwprop1" } } */
> /* Other zero-one predicates should expose conditional negation. */
> /* { dg-final { scan-tree-dump-times " \\? " 5 "forwprop1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr123514.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr123514.c
> index 4a09d859031..ef2dde1804b 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/pr123514.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr123514.c
> @@ -8,4 +8,4 @@ bit_trick (int x)
> return ((x + mask) ^ mask);
> }
>
> -/* { dg-final { scan-tree-dump "ABS_EXPR" "optimized" } } */
> +/* { dg-final { scan-tree-dump "ABSU_EXPR " "optimized" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr126418-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr126418-1.c
> new file mode 100644
> index 00000000000..3714069b43f
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr126418-1.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-forwprop1" } */
> +
> +int f_cmp_gt_commuted(int x, int y)
> +{
> + int cmp = x > y;
> + return cmp + (-cmp ^ x);
> +}
> +
> +/* { dg-final { scan-tree-dump-times "\\(unsigned int\\) " 1 "forwprop1" } }
> */
> +/* { dg-final { scan-tree-dump-times "\\(int\\) " 1 "forwprop1" } } */
> --
> 2.43.0
>
