On Mon, Apr 9, 2018 at 7:47 PM, Richard Sandiford
<richard.sandif...@linaro.org> wrote:
> In this PR we used WIDEN_SUM_EXPR to vectorise:
>
> short i, y;
> int sum;
> [...]
> for (i = x; i > 0; i--)
> sum += y;
>
> with 4 ints and 8 shorts per vector. The problem was that we set
> the VF based only on the ints, then calculated the number of vector
> copies based on the shorts, giving 4/8. Previously that led to
> ncopies==0, but after r249897 we pick it up as an ICE.
>
> In this particular case we could vectorise the reduction by setting
> ncopies based on the output type rather than the input type, but it
> doesn't seem worth adding a special "optimisation" for such a
> pathological case. I think it's really an instance of the more general
> problem that we can't vectorise using combinations of (say) 64-bit and
> 128-bit vectors on targets that support both.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
OK.
Richard.
> Richard
>
>
> 2018-04-09 Richard Sandiford <richard.sandif...@linaro.org>
>
> gcc/
> PR tree-optimization/85286
> * tree-vect-data-refs.c (vect_get_smallest_scalar_type):
>
> gcc/testsuite/
> * gcc.dg/vect/pr85286.c: New test.
>
> Index: gcc/tree-vect-data-refs.c
> ===================================================================
> --- gcc/tree-vect-data-refs.c 2018-03-24 10:52:25.616823316 +0000
> +++ gcc/tree-vect-data-refs.c 2018-04-09 18:44:09.676561821 +0100
> @@ -132,6 +132,8 @@ vect_get_smallest_scalar_type (gimple *s
>
> if (is_gimple_assign (stmt)
> && (gimple_assign_cast_p (stmt)
> + || gimple_assign_rhs_code (stmt) == DOT_PROD_EXPR
> + || gimple_assign_rhs_code (stmt) == WIDEN_SUM_EXPR
> || gimple_assign_rhs_code (stmt) == WIDEN_MULT_EXPR
> || gimple_assign_rhs_code (stmt) == WIDEN_LSHIFT_EXPR
> || gimple_assign_rhs_code (stmt) == FLOAT_EXPR))
> Index: gcc/testsuite/gcc.dg/vect/pr85286.c
> ===================================================================
> --- /dev/null 2018-04-08 19:55:28.217132277 +0100
> +++ gcc/testsuite/gcc.dg/vect/pr85286.c 2018-04-09 18:44:09.675561881 +0100
> @@ -0,0 +1,19 @@
> +/* PR tree-optimization/45241 */
> +/* { dg-do compile } */
> +/* { dg-additional-options "--param scev-max-expr-complexity=0" } */
> +
> +int
> +foo (short x)
> +{
> + short i, y;
> + int sum;
> +
> + for (i = 0; i < x; i++)
> + y = x * i;
> +
> + for (i = x; i > 0; i--)
> + sum += y;
> +
> + return sum;
> +}
> +
