On Mon, 27 Oct 2025, Artemiy Volkov wrote:
> This patch adds a match.pd transformation to strip unnecessary
> view_converts of BIT_FIELD_REFs. This is only valid when the type of the
> view_convert is a register type, and no loss of precision is involved when
> casting to an integer type; both of these conditions are checked for in
> the if clause of the new pattern.
>
> The change survives bootstrap + regtest on aarch64 and x86_64, and one
> additional test case has been added to gcc.dg/tree-ssa.
OK.
Thanks,
Richard.
> Changes since v1:
> - Require is_gimple_reg_type (type) and remove conditions on @0
> - Reword the commit message to reflect code changes
>
> gcc/ChangeLog:
>
> * match.pd: Add pattern to simplify view_convert (BIT_FIELD_REF).
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/forwprop-42.c: New test.
> ---
> gcc/match.pd | 8 ++++++++
> gcc/testsuite/gcc.dg/tree-ssa/forwprop-42.c | 12 ++++++++++++
> 2 files changed, 20 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/forwprop-42.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index b37a4371336..7b034231156 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -5645,6 +5645,14 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> (view_convert (view_convert @0))
> (view_convert @0))
>
> +/* Squash view_converts of BFRs if no precision is lost. */
> +(simplify
> + (view_convert (BIT_FIELD_REF @1 @2 @3))
> + (if (is_gimple_reg_type (type)
> + && (!INTEGRAL_TYPE_P (type)
> + || type_has_mode_precision_p (type)))
> + (BIT_FIELD_REF:type @1 @2 @3)))
> +
> /* For integral conversions with the same precision or pointer
> conversions use a NOP_EXPR instead. */
> (simplify
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/forwprop-42.c
> b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-42.c
> new file mode 100644
> index 00000000000..5785e51c089
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-42.c
> @@ -0,0 +1,12 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-forwprop1" } */
> +
> +typedef unsigned int vec2 __attribute__ ((vector_size (2 * sizeof (unsigned
> int))));
> +typedef unsigned int vec1 __attribute__ ((vector_size (sizeof (unsigned
> int))));
> +
> +vec1 foo (vec2 x)
> +{
> + return (vec1) x[1];
> +}
> +
> +/* { dg-final { scan-tree-dump-not "VIEW_CONVERT_EXPR" "forwprop1" } } */
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
