On Thu, Aug 7, 2025 at 2:14 PM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> simplify_gen_subreg rejected subregs of literal constants if
> MODE_COMPOSITE_P. This was added by the fix for PR96648 in
> g:c0f772894b6b3cd8ed5c5dd09d0c7917f51cf70f. Jakub said:
>
> As for the simplify_gen_subreg change, I think it would be desirable
> to just avoid creating SUBREGs of constants on all targets and for all
> constants, if simplify_immed_subreg simplified, fine, otherwise punt,
> but as we are late in GCC11 development, the patch instead guards this
> behavior on MODE_COMPOSITE_P (outermode) - i.e. only conversions to
> powerpc{,64,64le} double double long double - and only for the cases where
> simplify_immed_subreg was called.
>
> I'm not sure about relaxing the codes further, since subregs might
> be wanted for CONST, SYMBOL_REF and LABEL_REF. But removing the
> MODE_COMPOSITE_P is needed to fix PR120718, where we get an ICE
> from generating a subreg of a V2SI const_vector.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
OK.
Richard.
> Richard
>
>
> gcc/
> PR rtl-optimization/120718
> * simplify-rtx.cc (simplify_context::simplify_gen_subreg):
> Remove MODE_COMPOSITE_P condition.
>
> gcc/testsuite/
> PR rtl-optimization/120718
> * gcc.target/aarch64/sve/acle/general/pr120718.c: New test.
> ---
> gcc/simplify-rtx.cc | 12 ++++--------
> .../gcc.target/aarch64/sve/acle/general/pr120718.c | 12 ++++++++++++
> 2 files changed, 16 insertions(+), 8 deletions(-)
> create mode 100644
> gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr120718.c
>
> diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
> index 8ef96b4c1c8..35070c09aa0 100644
> --- a/gcc/simplify-rtx.cc
> +++ b/gcc/simplify-rtx.cc
> @@ -8502,14 +8502,10 @@ simplify_context::simplify_gen_subreg (machine_mode
> outermode, rtx op,
>
> if (GET_CODE (op) == SUBREG
> || GET_CODE (op) == CONCAT
> - || GET_MODE (op) == VOIDmode)
> - return NULL_RTX;
> -
> - if (MODE_COMPOSITE_P (outermode)
> - && (CONST_SCALAR_INT_P (op)
> - || CONST_DOUBLE_AS_FLOAT_P (op)
> - || CONST_FIXED_P (op)
> - || GET_CODE (op) == CONST_VECTOR))
> + || CONST_SCALAR_INT_P (op)
> + || CONST_DOUBLE_AS_FLOAT_P (op)
> + || CONST_FIXED_P (op)
> + || GET_CODE (op) == CONST_VECTOR)
> return NULL_RTX;
>
> if (validate_subreg (outermode, innermode, op, byte))
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr120718.c
> b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr120718.c
> new file mode 100644
> index 00000000000..9ca0938e36b
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr120718.c
> @@ -0,0 +1,12 @@
> +/* { dg-options "-O2" } */
> +
> +#include <arm_sve.h>
> +typedef int __attribute__((vector_size(8))) v2si;
> +typedef struct { int x; int y; } A;
> +void bar(A a);
> +void foo()
> +{
> + A a;
> + *(v2si *)&a = (v2si){0, (int)svcntd_pat(SV_ALL)};
> + bar(a);
> +}
> --
> 2.43.0
>
