From a3317f7b3c02907a122f89879e5b6e90c386e64d Mon Sep 17 00:00:00 2001 From: Richard Sandiford Date: Thu, 15 Apr 2021 11:37:38 +0100 Subject: c: Don't drop vector attributes that affect type identity [PR98852] 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 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: vector + vector had a GNU vector type rather than an 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. --- gcc/c/c-typeck.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'gcc/c') diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c index 21eab00..51a62c8 100644 --- a/gcc/c/c-typeck.c +++ b/gcc/c/c-typeck.c @@ -740,10 +740,16 @@ c_common_type (tree t1, tree t2) t2 = TYPE_MAIN_VARIANT (t2); if (TYPE_ATTRIBUTES (t1) != NULL_TREE) - t1 = build_type_attribute_variant (t1, NULL_TREE); + { + tree attrs = affects_type_identity_attributes (TYPE_ATTRIBUTES (t1)); + t1 = build_type_attribute_variant (t1, attrs); + } if (TYPE_ATTRIBUTES (t2) != NULL_TREE) - t2 = build_type_attribute_variant (t2, NULL_TREE); + { + tree attrs = affects_type_identity_attributes (TYPE_ATTRIBUTES (t2)); + t2 = build_type_attribute_variant (t2, attrs); + } /* Save time if the two types are the same. */ -- cgit v1.1