tree-scalar-evolution.c: Handle LSHIFT by constant

On 3 November 2015 at 11:35, Richard Biener <richard.guenther@gmail.com> wrote:
>
> I think this should simply re-write A << B to (type) (unsigned-type) A
> * (1U << B).
>
> Does that then still vectorize the signed case?

I didn't realize our representation of chrec's could express that.
Yes, it does - thanks! (And the avx512ifma- test is compiled without warnings.)

Patch attached. I've added a platform-independent version of the failing AVX512
test too.

--Alan

gcc/ChangeLog:

	PR tree-optimization/65963
	* tree-scalar-evolution.c (interpret_rhs_expr): Try to handle
	LSHIFT_EXPRs as equivalent unsigned MULT_EXPRs.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr68112.c: New.
	* gcc.dg/vect/vect-strided-shift-1.c: New.
---
 gcc/testsuite/gcc.dg/pr68112.c                   | 11 ++++++++
 gcc/testsuite/gcc.dg/vect/vect-strided-shift-1.c | 33 ++++++++++++++++++++++++
 gcc/tree-scalar-evolution.c                      | 17 ++++++++++++
 3 files changed, 61 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/pr68112.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-strided-shift-1.c

On Thu, Nov 5, 2015 at 2:26 PM, Alan Lawrence <alan.lawrence@arm.com> wrote:
> On 3 November 2015 at 11:35, Richard Biener <richard.guenther@gmail.com> wrote:
>>
>> I think this should simply re-write A << B to (type) (unsigned-type) A
>> * (1U << B).
>>
>> Does that then still vectorize the signed case?
>
> I didn't realize our representation of chrec's could express that.
> Yes, it does - thanks! (And the avx512ifma- test is compiled without warnings.)
>
> Patch attached. I've added a platform-independent version of the failing AVX512
> test too.
>
> --Alan
>
> gcc/ChangeLog:
>
>         PR tree-optimization/65963
>         * tree-scalar-evolution.c (interpret_rhs_expr): Try to handle
>         LSHIFT_EXPRs as equivalent unsigned MULT_EXPRs.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/pr68112.c: New.
>         * gcc.dg/vect/vect-strided-shift-1.c: New.
> ---
>  gcc/testsuite/gcc.dg/pr68112.c                   | 11 ++++++++
>  gcc/testsuite/gcc.dg/vect/vect-strided-shift-1.c | 33 ++++++++++++++++++++++++
>  gcc/tree-scalar-evolution.c                      | 17 ++++++++++++
>  3 files changed, 61 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.dg/pr68112.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/vect-strided-shift-1.c
>
> diff --git a/gcc/testsuite/gcc.dg/pr68112.c b/gcc/testsuite/gcc.dg/pr68112.c
> new file mode 100644
> index 0000000..0a45b03
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr68112.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -Waggressive-loop-optimizations" } */
> +
> +int *a;
> +
> +void
> +foo ()
> +{
> +  for (int i = 0; i < 65536; i++)
> +    *a = i << 24;
> +}
> 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..60d515d 100644
> --- a/gcc/tree-scalar-evolution.c
> +++ b/gcc/tree-scalar-evolution.c
> @@ -1840,6 +1840,23 @@ 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).  */
> +       tree uns = unsigned_type_for (type);
> +       chrec1 = analyze_scalar_evolution (loop, rhs1);
> +       chrec2 = analyze_scalar_evolution (loop, rhs2);
> +       chrec1 = chrec_convert (uns, chrec1, at_stmt);
> +       chrec1 = instantiate_parameters (loop, chrec1);
> +       chrec2 = instantiate_parameters (loop, chrec2);
> +
> +       tree one = build_int_cst (unsigned_type_for (TREE_TYPE (rhs1)), 1);

use 'uns' for the type.

Ok with that change.

Richard.

> +       chrec2 = fold_build2 (LSHIFT_EXPR, uns, one, chrec2);
> +       res = chrec_fold_multiply (uns, chrec1, chrec2);
> +       res = chrec_convert (type, res, at_stmt);
> +      }
> +      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
>