On Mon, Jul 21, 2025 at 1:30 AM Andrew Pinski <quic_apin...@quicinc.com> wrote:
>
> I have seen this a few places though the testcase from PR 95906
> is an obvious place where this shows up for sure.
> This convert `cmp - 1` into `-icmp` as that form is more useful
> in many cases.
>
> Bootstrapped and tested on x86_64-linux-gnu.
I think we want to ensure that TYPE_PRECISION (type) > 1
(considering a cast from unsigned bool to signed and thus UB
for -1 + -1).
OK with that change.
Thanks,
Richard.
> PR tree-optimization/110949
> PR tree-optimization/95906
>
> gcc/ChangeLog:
>
> * match.pd (cmp - 1): New pattern.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/cmp-2.c: New test.
> * gcc.dg/tree-ssa/max-bitcmp-1.c: New test.
>
> Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
> ---
> gcc/match.pd | 17 ++++++++++++++++-
> gcc/testsuite/gcc.dg/tree-ssa/cmp-2.c | 14 ++++++++++++++
> gcc/testsuite/gcc.dg/tree-ssa/max-bitcmp-1.c | 19 +++++++++++++++++++
> 3 files changed, 49 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cmp-2.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/max-bitcmp-1.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 7f84d5149f4..3e8b324e376 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -7035,6 +7035,21 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> (icmp @0 @1)
> (if (ic == ncmp)
> (ncmp @0 @1)))))
> + /* ((cast)cmp) - 1 -> -(cast)icmp . */
> + (simplify
> + (plus (convert? (cmp@2 @0 @1)) integer_minus_onep)
> + (if (INTEGRAL_TYPE_P (TREE_TYPE (@2)) && TYPE_PRECISION (TREE_TYPE (@2))
> == 1)
> + /* Comparison inversion may be impossible for trapping math,
> + invert_tree_comparison will tell us. But we can't use
> + a computed operator in the replacement tree thus we have
> + to play the trick below. */
> + (with { enum tree_code ic = invert_tree_comparison
> + (cmp, HONOR_NANS (@0));
> + tree cmptype = TREE_TYPE (@2); }
> + (if (ic == icmp)
> + (negate (convert (icmp:cmptype @0 @1)))
> + (if (ic == ncmp)
> + (negate (convert (ncmp:cmptype @0 @1))))))))
> /* The following bits are handled by fold_binary_op_with_conditional_arg.
> */
> (simplify
> (ne (cmp@2 @0 @1) integer_zerop)
> @@ -11678,4 +11693,4 @@ and,
> && VECTOR_TYPE_P (type)
> && direct_internal_fn_supported_p (IFN_AVG_CEIL, type,
> OPTIMIZE_FOR_BOTH))
> (IFN_AVG_CEIL @0 @2)))
> -#endif
> \ No newline at end of file
> +#endif
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/cmp-2.c
> b/gcc/testsuite/gcc.dg/tree-ssa/cmp-2.c
> new file mode 100644
> index 00000000000..9b029019c06
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/cmp-2.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fdump-tree-forwprop" } */
> +
> +/* PR tree-optimization/110949 */
> +/* Transform `(cmp) - 1` into `-icmp`. */
> +
> +int f1(int a)
> +{
> + int t = a == 115;
> + return t - 1;
> +}
> +
> +/* { dg-final { scan-tree-dump " != 115" "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-not " == 115" "forwprop1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/max-bitcmp-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/max-bitcmp-1.c
> new file mode 100644
> index 00000000000..81b5a27c045
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/max-bitcmp-1.c
> @@ -0,0 +1,19 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fdump-tree-forwprop -fdump-tree-optimized" } */
> +
> +/* PR tree-optimization/95906 */
> +/* this should become MAX_EXPR<a,b> */
> +
> +int f2(int a, int b)
> +{
> + int cmp = -(a > b);
> + return (cmp & a) | (~cmp & b);
> +}
> +
> +/* we should not end up with -_2 */
> +/* we should not end up and & nor a `+ -1` */
> +/* In optimized we should have a max. */
> +/* { dg-final { scan-tree-dump-not " -\[a-zA-Z_\]" "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-not " & " "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-not " . -1" "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-times "MAX_EXPR " 1 "optimized" } } */
> --
> 2.43.0
>
