https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98852
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:a3317f7b3c02907a122f89879e5b6e90c386e64d commit r11-8191-ga3317f7b3c02907a122f89879e5b6e90c386e64d Author: Richard Sandiford <richard.sandif...@arm.com> Date: Thu Apr 15 11:37:38 2021 +0100 c: Don't drop vector attributes that affect type identity [PR98852] <arm_neon.h> types are distinct from GNU vector types in at least their mangling. However, there used to be nothing explicit in the VECTOR_TYPE itself to indicate the difference: we simply treated them as distinct TYPE_MAIN_VARIANTs. This caused problems like the ones reported in PR95726. The fix for that PR was to add type attributes to the <arm_neon.h> types, in order to maintain the distinction between them and GNU vectors. However, this in turn caused PR98852, where c_common_type would unconditionally drop the attributes on the source types. This meant that: <arm_neon.h> vector + <arm_neon.h> vector had a GNU vector type rather than an <arm_neon.h> vector type. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96377#c2 for Jakub's analysis of the history of this c_common_type code. TBH I'm not sure which case the build_type_attribute_variant code is handling, but I think we should at least avoid dropping attributes that affect type identity. I've tried to audit the C and target-specific attributes to look for other types that might be affected by this, but I couldn't see any. We are only dealing with: gcc_assert (code1 == VECTOR_TYPE || code1 == COMPLEX_TYPE || code1 == FIXED_POINT_TYPE || code1 == REAL_TYPE || code1 == INTEGER_TYPE); which excludes most affects_type_identity attributes. The closest was s390_vector_bool, but the handler for that attribute changes the type node and drops the attribute itself (*no_add_attrs = true). I put the main list handling into a separate function (remove_attributes_matching) because a later patch will need it for something else. gcc/ PR c/98852 * attribs.h (affects_type_identity_attributes): Declare. * attribs.c (remove_attributes_matching): New function. (affects_type_identity_attributes): Likewise. gcc/c/ PR c/98852 * c-typeck.c (c_common_type): Do not drop attributes that affect type identity. gcc/testsuite/ PR c/98852 * gcc.target/aarch64/advsimd-intrinsics/pr98852.c: New test.
