On Thu, Aug 20, 2026 at 7:07 AM Konstantinos Eleftheriou
<[email protected]> wrote:
>
> Memory operands were only rejected when their size is unknown or
> non-constant, so a BLKmode store with a known size could become a
> forwarding candidate. Building the bit insert sequence for it asserts
> in store_bit_field, as BLKmode has no corresponding integer mode.
> Reject such memory when collecting candidates.
>
> PR rtl-optimization/126686
>
> gcc/ChangeLog:
>
> * avoid-store-forwarding.cc
> (store_forwarding_analyzer::avoid_store_forwarding): Reject
> BLKmode stores and loads as forwarding candidates.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/s390/pr126686.c: New test.
> ---
> gcc/avoid-store-forwarding.cc | 10 +++++++---
> gcc/testsuite/gcc.target/s390/pr126686.c | 16 ++++++++++++++++
> 2 files changed, 23 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/s390/pr126686.c
>
> diff --git a/gcc/avoid-store-forwarding.cc b/gcc/avoid-store-forwarding.cc
> index 141f96c3d848..99feebafe126 100644
> --- a/gcc/avoid-store-forwarding.cc
> +++ b/gcc/avoid-store-forwarding.cc
> @@ -565,11 +565,15 @@ store_forwarding_analyzer::avoid_store_forwarding
> (basic_block bb)
> /* The mem RTX if INSN is a store, NULL_RTX otherwise. */
> rtx store_mem = MEM_P (SET_DEST (set)) ? SET_DEST (set) : NULL_RTX;
>
> - /* We cannot analyze memory RTXs that have unknown size. */
> + /* We cannot analyze memory RTXs that have unknown size. BLKmode
> + memory is rejected as well, as there is no mode for the forwarded
> + value, even when its size is known. */
> if ((store_mem && (!MEM_SIZE_KNOWN_P (store_mem)
> - || !MEM_SIZE (store_mem).is_constant ()))
> + || !MEM_SIZE (store_mem).is_constant ()
> + || GET_MODE (store_mem) == BLKmode))
> || (load_mem && (!MEM_SIZE_KNOWN_P (load_mem)
> - || !MEM_SIZE (load_mem).is_constant ())))
> + || !MEM_SIZE (load_mem).is_constant ()
> + || GET_MODE (load_mem) == BLKmode)))
Can you place the GET_MODE check first in the list since it should be
the cheapest test?
Otherwise ok.
> {
> store_exprs.truncate (0);
> continue;
> diff --git a/gcc/testsuite/gcc.target/s390/pr126686.c
> b/gcc/testsuite/gcc.target/s390/pr126686.c
> new file mode 100644
> index 000000000000..ab25d109ec35
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/s390/pr126686.c
> @@ -0,0 +1,16 @@
> +/* PR rtl-optimization/126686 */
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -favoid-store-forwarding" } */
> +
> +int tmp;
> +short d_e;
> +
> +int
> +foo ()
> +{
> + long f = 0;
> + __builtin_memset ((char *) &f + sizeof f - 2, d_e, 2);
> + tmp = f;
> +
> + return f;
> +}
> --
> 2.55.0
>
