OK for master and backports? (also a long-standing bug that didn't surface 
until the new constexpr test was added)

tested on powerpc64le-linux-gnu

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

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

libstdc++-v3/ChangeLog:

	PR libstdc++/109949
	* include/experimental/bits/simd.h (__intrinsic_type): If
	__ALTIVEC__ is defined, map gnu::vector_size types to their
	corresponding __vector T types without losing unsignedness of
	integer types. Also prefer long long over long.
	* include/experimental/bits/simd_ppc.h (_S_popcount): Cast mask
	object to the expected unsigned vector type.
---
 libstdc++-v3/include/experimental/bits/simd.h | 39 ++++++++++++++++---
 .../include/experimental/bits/simd_ppc.h      |  3 +-
 2 files changed, 36 insertions(+), 6 deletions(-)


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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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