On Fri, Oct 25, 2019 at 2:32 PM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> Except for one case, get_vectype_for_scalar_type_and_size calculates
> what the vector mode should be and then calls build_vector_type,
> which recomputes the mode from scratch. This patch makes it use
> build_vector_type_for_mode instead.
>
> The exception mentioned above is when preferred_simd_mode returns
> an integer mode, which it does if no appropriate vector mode exists.
> The integer mode in question is usually word_mode, although epiphany
> can return a doubleword mode in some cases.
>
> There's no guarantee that this integer mode is appropriate, since for
> example the scalar type could be a float. The traditional behaviour is
> therefore to use the integer mode to determine a size only, and leave
> mode_for_vector to pick the TYPE_MODE. (Note that it can actually end
> up picking a vector mode if the target defines a disabled vector mode.
> We therefore still need to check TYPE_MODE after building the type.)
OK.
Thanks,
Richard.
>
> 2019-10-24 Richard Sandiford <richard.sandif...@arm.com>
>
> gcc/
> * tree-vect-stmts.c (get_vectype_for_scalar_type_and_size): If
> targetm.vectorize.preferred_simd_mode returns an integer mode,
> use mode_for_vector to decide what the vector type's mode
> should actually be. Use build_vector_type_for_mode instead
> of build_vector_type.
>
> Index: gcc/tree-vect-stmts.c
> ===================================================================
> --- gcc/tree-vect-stmts.c 2019-10-25 13:26:59.309877555 +0100
> +++ gcc/tree-vect-stmts.c 2019-10-25 13:27:08.653811531 +0100
> @@ -11162,16 +11162,31 @@ get_vectype_for_scalar_type_and_size (tr
> /* If no size was supplied use the mode the target prefers. Otherwise
> lookup a vector mode of the specified size. */
> if (known_eq (size, 0U))
> - simd_mode = targetm.vectorize.preferred_simd_mode (inner_mode);
> + {
> + simd_mode = targetm.vectorize.preferred_simd_mode (inner_mode);
> + if (SCALAR_INT_MODE_P (simd_mode))
> + {
> + /* Traditional behavior is not to take the integer mode
> + literally, but simply to use it as a way of determining
> + the vector size. It is up to mode_for_vector to decide
> + what the TYPE_MODE should be.
> +
> + Note that nunits == 1 is allowed in order to support single
> + element vector types. */
> + if (!multiple_p (GET_MODE_SIZE (simd_mode), nbytes, &nunits)
> + || !mode_for_vector (inner_mode, nunits).exists (&simd_mode))
> + return NULL_TREE;
> + }
> + }
> else if (!multiple_p (size, nbytes, &nunits)
> || !mode_for_vector (inner_mode, nunits).exists (&simd_mode))
> return NULL_TREE;
> - /* NOTE: nunits == 1 is allowed to support single element vector types. */
> - if (!multiple_p (GET_MODE_SIZE (simd_mode), nbytes, &nunits))
> - return NULL_TREE;
>
> - vectype = build_vector_type (scalar_type, nunits);
> + vectype = build_vector_type_for_mode (scalar_type, simd_mode);
>
> + /* In cases where the mode was chosen by mode_for_vector, check that
> + the target actually supports the chosen mode, or that it at least
> + allows the vector mode to be replaced by a like-sized integer. */
> if (!VECTOR_MODE_P (TYPE_MODE (vectype))
> && !INTEGRAL_MODE_P (TYPE_MODE (vectype)))
> return NULL_TREE;
