Re: [PATCH] tree-scalar-evolution.c: Handle LSHIFT by constant

[Richard Biener <richard dot guenther at gmail dot com>]

On Fri, Oct 23, 2015 at 5:15 PM, Alan Lawrence <alan.lawrence@arm.com> wrote:
> On 19/10/15 12:49, Richard Biener wrote:
>
>> Err, you should always do the shift in the type of rhs1.  You should also
>> avoid the chrec_convert of rhs2 above for shifts.
>
> Err, yes, indeed.  Needed to keep the chrec_convert before the
> chrec_fold_multiply, and the rest followed.  How's this?
>
> Bootstrapped+check-gcc,g++ on x86, ARM, AArch64.
>
> gcc/ChangeLog (as before):
>
>         PR tree-optimization/65963
>         * tree-scalar-evolution.c (interpret_rhs_expr): Handle some LSHIFT_EXPRs
>         as equivalent MULT_EXPRs.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/vect/vect-strided-shift-1.c: New.
> ---
>  gcc/testsuite/gcc.dg/vect/vect-strided-shift-1.c | 33 ++++++++++++++++++++++++
>  gcc/tree-scalar-evolution.c                      | 15 +++++++++++
>  2 files changed, 48 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.dg/vect/vect-strided-shift-1.c
>
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-strided-shift-1.c b/gcc/testsuite/gcc.dg/vect/vect-strided-shift-1.c
> new file mode 100644
> index 0000000..b1ce2ec
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/vect-strided-shift-1.c
> @@ -0,0 +1,33 @@
> +/* PR tree-optimization/65963.  */
> +#include "tree-vect.h"
> +
> +#define N 512
> +
> +int in[2*N], out[N];
> +
> +__attribute__ ((noinline)) void
> +loop (void)
> +{
> +  for (int i = 0; i < N; i++)
> +    out[i] = in[i << 1] + 7;
> +}
> +
> +int
> +main (int argc, char **argv)
> +{
> +  check_vect ();
> +  for (int i = 0; i < 2*N; i++)
> +    {
> +      in[i] = i;
> +      __asm__ volatile ("" : : : "memory");
> +    }
> +  loop ();
> +  __asm__ volatile ("" : : : "memory");
> +  for (int i = 0; i < N; i++)
> +    {
> +      if (out[i] != i*2 + 7)
> +       abort ();
> +    }
> +  return 0;
> +}
> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops in function" 1 "vect" { target { vect_strided2 } } } } */
> diff --git a/gcc/tree-scalar-evolution.c b/gcc/tree-scalar-evolution.c
> index 0753bf3..129682f 100644
> --- a/gcc/tree-scalar-evolution.c
> +++ b/gcc/tree-scalar-evolution.c
> @@ -1840,6 +1840,21 @@ interpret_rhs_expr (struct loop *loop, gimple *at_stmt,
>        res = chrec_fold_multiply (type, chrec1, chrec2);
>        break;
>
> +    case LSHIFT_EXPR:
> +      /* Handle A<<B as A * (1<<B).  */
> +      chrec1 = analyze_scalar_evolution (loop, rhs1);
> +      chrec2 = analyze_scalar_evolution (loop, rhs2);
> +      chrec1 = chrec_convert (type, chrec1, at_stmt);
> +      chrec1 = instantiate_parameters (loop, chrec1);
> +      chrec2 = instantiate_parameters (loop, chrec2);
> +      chrec2 = fold_build2 (LSHIFT_EXPR, TREE_TYPE (rhs1),
> +                           build_int_cst (TREE_TYPE (rhs1), 1),

'type' instead of TREE_TYPE (rhs1)

> +                           chrec2);
> +      chrec2 = chrec_convert (type, chrec2, at_stmt);

so you can remove this chrec_convert.

Ok with that change.

Richard.

> +      res = chrec_fold_multiply (type, chrec1, chrec2);
> +      break;
> +
>      CASE_CONVERT:
>        /* In case we have a truncation of a widened operation that in
>           the truncated type has undefined overflow behavior analyze
> --
> 1.9.1
>