Tested on x86_64-linux-gnu and aarch64-linux-gnu and with Clang 18 on x86_64-
linux-gnu.

OK for trunk and backport(s)?

---------------------- 8< ----------------------------

Signed-off-by: Matthias Kretz <m.kretz@gsi.de>

libstdc++-v3/ChangeLog:

	PR libstdc++/114958
	* include/experimental/bits/simd.h (__as_vector): Return scalar
	simd as one-element vector. Return vector from single-vector
	fixed_size simd.
	(__vec_shuffle): New.
	(__extract_part): Adjust return type signature.
	(split): Use __extract_part for any split into non-fixed_size
	simds.
	(concat): If the return type stores a single vector, use
	__vec_shuffle (which calls __builtin_shufflevector) to produce
	the return value.
	* include/experimental/bits/simd_builtin.h
	(__shift_elements_right): Removed.
	(__extract_part): Return single elements directly. Use
	__vec_shuffle (which calls __builtin_shufflevector) to for all
	non-trivial cases.
	* include/experimental/bits/simd_fixed_size.h (__extract_part):
	Return single elements directly.
	* testsuite/experimental/simd/pr114958.cc: New test.
---
 libstdc++-v3/include/experimental/bits/simd.h | 161 +++++++++++++-----
 .../include/experimental/bits/simd_builtin.h  | 152 +----------------
 .../experimental/bits/simd_fixed_size.h       |   4 +-
 .../testsuite/experimental/simd/pr114958.cc   |  20 +++
 4 files changed, 145 insertions(+), 192 deletions(-)
 create mode 100644 libstdc++-v3/testsuite/experimental/simd/pr114958.cc


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 Dr. Matthias Kretz                           https://mattkretz.github.io
 GSI Helmholtz Centre for Heavy Ion Research               https://gsi.de
 stdₓ::simd
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