Re: [PATCH] MATCH: Add simplifications for `(a * zero_one) ==/!= CST`

[Richard Biener <richard.guenther@gmail.com>]

On Sat, Sep 16, 2023 at 7:50 AM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Transforming `(a * b@[0,1]) != 0` into `((cast)b) & a != 0`

that isn't strictly a simplification (one more op), and your
alternate transform is even worse in this regard.

> will produce better code as a lot of the time b is defined
> by a comparison.

what if not?  How does it simplify then?

> Also since canonicalize `a & -zero_one` into `a * zero_one` we
> start to lose information when doing comparisons against 0.
> In the case of PR 110992, we lose that `a != 0` on the branch

How so?  Ranger should be happy with both forms, no?

> and then don't do a jump threading like we should.
>
> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.
>
>         PR tree-optimization/110992
>
> gcc/ChangeLog:
>
>         * match.pd (`a * zero_one !=/== CST`): New pattern.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/tree-ssa/vrp116.c: Update test to avoid the
>         extra comparison.
>         * gcc.c-torture/execute/pr110992-1.c: New test.
>         * gcc.dg/tree-ssa/pr110992-1.c: New test.
>         * gcc.dg/tree-ssa/pr110992-2.c: New test.
> ---
>  gcc/match.pd                                  | 15 +++++++
>  .../gcc.c-torture/execute/pr110992-1.c        | 43 +++++++++++++++++++
>  gcc/testsuite/gcc.dg/tree-ssa/pr110992-1.c    | 21 +++++++++
>  gcc/testsuite/gcc.dg/tree-ssa/pr110992-2.c    | 17 ++++++++
>  gcc/testsuite/gcc.dg/tree-ssa/vrp116.c        |  2 +-
>  5 files changed, 97 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr110992-1.c
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr110992-1.c
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr110992-2.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 39c9c81966a..97405e6a5c3 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -2197,6 +2197,21 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>   (if (INTEGRAL_TYPE_P (type))
>    (bit_and @0 @1)))
>
> +/* (a * b@[0,1]) == CST
> +     ->
> +       CST == 0 ? (a == CST | b == 0) : (a == CST & b != 0)
> +   (a * b@[0,1]) != CST
> +     ->
> +       CST != 0 ? (a != CST | b == 0) : (a != CST & b != 0)  */
> +(for cmp (ne eq)
> + (simplify
> +  (cmp (mult:cs @0 zero_one_valued_p@1) INTEGER_CST@2)
> +  (if ((cmp == EQ_EXPR) ^ (wi::to_wide (@2) != 0))
> +   (bit_ior
> +    (cmp @0 @2)
> +    (convert (bit_xor @1 { build_one_cst (TREE_TYPE (@1)); })))
> +   (bit_and (cmp @0 @2) (convert @1)))))
> +
>  (for cmp (tcc_comparison)
>       icmp (inverted_tcc_comparison)
>   /* Fold (((a < b) & c) | ((a >= b) & d)) into (a < b ? c : d) & 1.  */
> diff --git a/gcc/testsuite/gcc.c-torture/execute/pr110992-1.c b/gcc/testsuite/gcc.c-torture/execute/pr110992-1.c
> new file mode 100644
> index 00000000000..edb7eb75ef2
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/execute/pr110992-1.c
> @@ -0,0 +1,43 @@
> +#define CST 5
> +#define OP !=
> +#define op_eq ==
> +#define op_ne !=
> +
> +#define function(vol,op, cst) \
> +__attribute__((noipa)) \
> +_Bool func_##op##_##cst##_##vol(vol int a, vol _Bool b) \
> +{ \
> +  vol int d = (a * b); \
> +  return d op_##op cst; \
> +}
> +
> +#define funcdefs(op,cst) \
> +function(,op,cst) \
> +function(volatile,op,cst)
> +
> +#define funcs(f) \
> +f(eq,0) \
> +f(eq,1) \
> +f(eq,5) \
> +f(ne,0) \
> +f(ne,1) \
> +f(ne,5)
> +
> +funcs(funcdefs)
> +
> +#define test(op,cst) \
> +do { \
> + if(func_##op##_##cst##_(a,b) != func_##op##_##cst##_volatile(a,b))\
> +   __builtin_abort(); \
> +} while(0);
> +
> +int main(void)
> +{
> +        for(int a = -10; a <= 10; a++)
> +        {
> +                _Bool b = 0;
> +                funcs(test)
> +                b = 1;
> +                funcs(test)
> +        }
> +}
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr110992-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr110992-1.c
> new file mode 100644
> index 00000000000..825fd63f84c
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr110992-1.c
> @@ -0,0 +1,21 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -fdump-tree-optimized" } */
> +static unsigned b;
> +static short c = 4;
> +void foo(void);
> +static short(a)(short d, short g) { return d * g; }
> +void e();
> +static char f() {
> +  b = 0;
> +  return 0;
> +}
> +int main() {
> +  int h = b;
> +  if ((short)(a(c && e, 65535) & h)) {
> +    foo();
> +    h || f();
> +  }
> +}
> +
> +/* There should be no calls to foo left. */
> +/* { dg-final { scan-tree-dump-not " foo " "optimized" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr110992-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr110992-2.c
> new file mode 100644
> index 00000000000..6082949a218
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr110992-2.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -fdump-tree-optimized" } */
> +static unsigned b;
> +static short c = 4;
> +void foo(void);
> +int main() {
> +  int h = b;
> +  int d = c != 0;
> +  if (h*d) {
> +    foo();
> +    if (!h) b = 20;
> +  }
> +}
> +
> +
> +/* There should be no calls to foo left. */
> +/* { dg-final { scan-tree-dump-not " foo " "optimized" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp116.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp116.c
> index 9e68a774aee..16b31e320a0 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/vrp116.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp116.c
> @@ -6,7 +6,7 @@ f (int m1, int m2, int c)
>  {
>    int d = m1 > m2;
>    int e = d * c;
> -  return e ? m1 : m2;
> +  return e;
>  }
>
>  /* { dg-final { scan-tree-dump-times "\\? c_\[0-9\]\\(D\\) : 0" 1 "optimized" } } */
> --
> 2.31.1
>