[Bug tree-optimization/125641] `a>>signbit | a` is just `max<a, -1>`

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125641

--- Comment #5 from Drea Pinski <pinskia at gcc dot gnu.org> ---
Comment on attachment 64664
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=64664
Untested patch

>diff --git a/gcc/match.pd b/gcc/match.pd
>index 14567d8a1f1..10e57dcafc4 100644
>--- a/gcc/match.pd
>+++ b/gcc/match.pd
>@@ -5028,6 +5028,38 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>         (op @0 { build_int_cst (TREE_TYPE (@1), prec - 1); })))
>       (op @0 { build_int_cst (TREE_TYPE (@1), low); })))))))
> 
>+/* Fold x | (~ (x >> (TYPE_PRECISION (type) - 1))) to max (x, -1)
>+   Fold x | (x >> (TYPE_PRECISION (type) - 1)) to max (x, -1)
>+   Fold x & (~ (x >> (TYPE_PRECISION (type) - 1))) to max (x, 0)
>+   Fold x & (x >> (TYPE_PRECISION (type) - 1)) to max (x, 0)

Typo in comments, the first and the last should be min.
>+*/
>+#ifdef GIMPLE
>+(simplify
>+ (bit_ior:c @0 (bit_not (rshift @0 INTEGER_CST@1)))
>+ (if (INTEGRAL_TYPE_P (type)
>+      && !TYPE_UNSIGNED (type)
>+      && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (type) - 1))
>+  (min @0 { build_int_cst (type, -1); })))
>+(simplify
>+ (bit_ior:c @0 (rshift @0 INTEGER_CST@1))
>+ (if (INTEGRAL_TYPE_P (type)
>+      && !TYPE_UNSIGNED (type)
>+      && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (type) - 1))
>+  (max @0 { build_int_cst (type, -1); })))
>+(simplify
>+ (bit_and:c @0 (bit_not (rshift @0 INTEGER_CST@1)))
>+ (if (INTEGRAL_TYPE_P (type)
>+      && !TYPE_UNSIGNED (type)
>+      && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (type) - 1))
>+  (max @0 { build_zero_cst (type); })))
>+(simplify
>+ (bit_and:c @0 (rshift @0 INTEGER_CST@1))
>+ (if (INTEGRAL_TYPE_P (type)
>+      && !TYPE_UNSIGNED (type)
>+      && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (type) - 1))
>+  (min @0 { build_zero_cst (type); })))

You can combine the set into 2 patterns using the following for loop.
(for bitop (bit_ior bit_and)
     result (max min)
     rresult (min max)

>+#endif
>+
> /* Fold `1 >> a` into `a == 0` for scalar integral types. */
> (simplify
>  (rshift integer_onep @2)