On Mon, Dec 2, 2019 at 5:33 PM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> Even EXACT_DIV_EXPR doesn't distribute across addition for wrapping
> types, so in general we can't fold EXACT_DIV_EXPRs of POLY_INT_CSTs
> at compile time. This was causing an ICE when trying to gimplify the
> element size field in an ARRAY_REF.
>
> If the result of that EXACT_DIV_EXPR is an invariant, we don't bother
> recording it in the ARRAY_REF and simply read the element size from the
> element type. This avoids the overhead of doing:
>
> /* ??? tree_ssa_useless_type_conversion will eliminate casts to
> sizetype from another type of the same width and signedness. */
> if (TREE_TYPE (aligned_size) != sizetype)
> aligned_size = fold_convert_loc (loc, sizetype, aligned_size);
> return size_binop_loc (loc, MULT_EXPR, aligned_size,
> size_int (TYPE_ALIGN_UNIT (elmt_type)));
>
> each time array_ref_element_size is called.
>
> So rather than read array_ref_element_size, do some arithmetic on it,
> and only then check whether the result is an invariant, we might as
> well check whether the element size is an invariant to start with.
> We're then directly testing whether array_ref_element_size gives
> a reusable value.
>
> For consistency, the patch makes the same change for the offset field
> in a COMPONENT_REF, although I don't think that can trigger yet.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
OK.
Thanks,
Richard.
> Richard
>
>
> 2019-12-02 Richard Sandiford <richard.sandif...@arm.com>
>
> gcc/
> * gimplify.c (gimplify_compound_lval): Don't gimplify and install
> an array element size if array_element_size is already an invariant.
> Similarly don't gimplify and install a field offset if
> component_ref_field_offset is already an invariant.
>
> gcc/testsuite/
> * gcc.target/aarch64/sve/acle/general-c/struct_1.c: New test.
>
> Index: gcc/gimplify.c
> ===================================================================
> --- gcc/gimplify.c 2019-11-22 09:57:52.178273436 +0000
> +++ gcc/gimplify.c 2019-12-02 16:32:08.063499557 +0000
> @@ -2987,17 +2987,18 @@ gimplify_compound_lval (tree *expr_p, gi
>
> if (TREE_OPERAND (t, 3) == NULL_TREE)
> {
> - tree elmt_type = TREE_TYPE (TREE_TYPE (TREE_OPERAND (t, 0)));
> - tree elmt_size = unshare_expr (array_ref_element_size (t));
> - tree factor = size_int (TYPE_ALIGN_UNIT (elmt_type));
> -
> - /* Divide the element size by the alignment of the element
> - type (above). */
> - elmt_size
> - = size_binop_loc (loc, EXACT_DIV_EXPR, elmt_size, factor);
> -
> + tree elmt_size = array_ref_element_size (t);
> if (!is_gimple_min_invariant (elmt_size))
> {
> + elmt_size = unshare_expr (elmt_size);
> + tree elmt_type = TREE_TYPE (TREE_TYPE (TREE_OPERAND (t,
> 0)));
> + tree factor = size_int (TYPE_ALIGN_UNIT (elmt_type));
> +
> + /* Divide the element size by the alignment of the element
> + type (above). */
> + elmt_size = size_binop_loc (loc, EXACT_DIV_EXPR,
> + elmt_size, factor);
> +
> TREE_OPERAND (t, 3) = elmt_size;
> tret = gimplify_expr (&TREE_OPERAND (t, 3), pre_p,
> post_p, is_gimple_reg,
> @@ -3017,16 +3018,18 @@ gimplify_compound_lval (tree *expr_p, gi
> /* Set the field offset into T and gimplify it. */
> if (TREE_OPERAND (t, 2) == NULL_TREE)
> {
> - tree offset = unshare_expr (component_ref_field_offset (t));
> - tree field = TREE_OPERAND (t, 1);
> - tree factor
> - = size_int (DECL_OFFSET_ALIGN (field) / BITS_PER_UNIT);
> -
> - /* Divide the offset by its alignment. */
> - offset = size_binop_loc (loc, EXACT_DIV_EXPR, offset, factor);
> -
> + tree offset = component_ref_field_offset (t);
> if (!is_gimple_min_invariant (offset))
> {
> + offset = unshare_expr (offset);
> + tree field = TREE_OPERAND (t, 1);
> + tree factor
> + = size_int (DECL_OFFSET_ALIGN (field) / BITS_PER_UNIT);
> +
> + /* Divide the offset by its alignment. */
> + offset = size_binop_loc (loc, EXACT_DIV_EXPR,
> + offset, factor);
> +
> TREE_OPERAND (t, 2) = offset;
> tret = gimplify_expr (&TREE_OPERAND (t, 2), pre_p,
> post_p, is_gimple_reg,
> Index: gcc/testsuite/gcc.target/aarch64/sve/acle/general-c/struct_1.c
> ===================================================================
> --- /dev/null 2019-09-17 11:41:18.176664108 +0100
> +++ gcc/testsuite/gcc.target/aarch64/sve/acle/general-c/struct_1.c
> 2019-12-02 16:32:08.075499476 +0000
> @@ -0,0 +1,10 @@
> +/* { dg-options "-std=c99" } */
> +
> +#include <arm_sve.h>
> +
> +void
> +f (svint8_t a, svint8_t b)
> +{
> + /* Not supported, but mustn't ICE. */
> + (svint8x2_t) { a, b };
> +}
