https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96377
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> --- This dates back to https://gcc.gnu.org/legacy-ml/gcc-patches/2004-06/msg00288.html Dunno, do we want to never strip attributes from VECTOR_TYPEs and only strip them that way from non-VECTOR_TYPEs? Or only strip some attributes and keep others? Or just add a if (t1 == t2) return t1; before the attribute stripping (perhaps for VECTOR_TYPEs only)? Note, due to the typedef __Uint8x16_t uint8x16_t; on this testcase t1 and t2 are equal and are the typedef file, and because they are unqualified, we don't use TYPE_MAIN_VARIANT (which is the __Uint8x16_t type). What is the desirable behavior for the common type if one is the aarch64 specific vector and the other generic vector with the same mode? The C++ behavior for vector types in cp_common_type is that it will merge attributes from both types, and if one is TYPE_UNSIGNED, pick that one, otherwise pick the other one. So in that case the ARM specific vector type wins. I must say I'm surprised that the 10.2 version of the patch also matters, perhaps the FE isn't using the target hook to compare attributes, but rather just compares TYPE_MAIN_VARIANT or something similar to determine if the initializer is initializing a whole vector or an element of the vector.
