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author | Marek Polacek <polacek@redhat.com> | 2021-01-28 16:21:50 -0500 |
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committer | Marek Polacek <polacek@redhat.com> | 2021-01-28 16:21:50 -0500 |
commit | 513ee7d2cd9a60339a50dc9c4cba39a8f1c707f0 (patch) | |
tree | 98d78524466262a1ede32be83fe4593d4f999f65 /gcc/tree.c | |
parent | a054608c9c409245575e3dfe61b9a36e1bf7ffcf (diff) | |
download | gcc-513ee7d2cd9a60339a50dc9c4cba39a8f1c707f0.zip gcc-513ee7d2cd9a60339a50dc9c4cba39a8f1c707f0.tar.gz gcc-513ee7d2cd9a60339a50dc9c4cba39a8f1c707f0.tar.bz2 |
tree: Don't reuse types if TYPE_USER_ALIGN differ [PR94775]
A year ago I submitted this patch:
~~
Here we trip on the TYPE_USER_ALIGN (t) assert in strip_typedefs: it
gets "const d[0]" with TYPE_USER_ALIGN=0 but the result built by
build_cplus_array_type is "const char[0]" with TYPE_USER_ALIGN=1.
When we strip_typedefs the element of the array "const d", we see it's
a typedef_variant_p, so we look at its DECL_ORIGINAL_TYPE, which is
char, but we need to add the const qualifier, so we call
cp_build_qualified_type -> build_qualified_type
where get_qualified_type checks to see if we already have such a type
by walking the variants list, which in this case is:
char -> c -> const char -> const char -> d -> const d
Because check_base_type only checks TYPE_ALIGN and not TYPE_USER_ALIGN,
we choose the first const char, which has TYPE_USER_ALIGN set. If the
element type of an array has TYPE_USER_ALIGN, the array type gets it too.
So we can make check_base_type stricter. I was afraid that it might make
us reuse types less often, but measuring showed that we build the same
amount of types with and without the patch, while bootstrapping.
~~
However, the patch broke a few tests on STRICT_ALIGNMENT platforms and
had to be reverted. This is another try. The original patch is kept
unchanged, but I added the finalize_type_size hunk that ought to fix the
STRICT_ALIGNMENT issues.
The problem is that finalize_type_size can clear TYPE_USER_ALIGN on the
main variant of a type, but doesn't clear it on any of the variants.
Then we end up with types which share the same TYPE_MAIN_VARIANT, but
their TYPE_CANONICAL differs and then the usual "canonical types differ
for identical types" follows.
I've created alignas19.C to exercise this scenario. What happens is:
- when parsing the class S we create a type S in xref_tag,
- we see alignas(8) so common_handle_aligned_attribute sets T_U_A in S,
- we parse the member function fn and build_memfn_type creates a copy
of S to add const; this variant has T_U_A set,
- we finish_struct S which calls layout_class_type -> finish_record_type
-> finalize_size_type where we reset T_U_A in S (but const S keeps it),
- finish_non_static_data_member for arr calls maybe_dummy_object with
type = S,
- maybe_dummy_object calls same_type_ignoring_top_level_qualifiers_p
to check if S and TREE_TYPE (current_class_ref), which is const S,
are the same,
- same_type_ignoring_top_level_qualifiers_p creates cv-unqualified
versions of the passed types. Previously we'd use our main variant
S when stripping "const S" of const, but since the T_U_A flags don't
match (check_base_type), we create a new variant S'. Then we crash in
comptypes because S and S' have the same TYPE_MAIN_VARIANT but
different TYPE_CANONICALs.
With my patch we'll clear T_U_A for S's variants too, and then instead
of S' we'll just use S.
gcc/ChangeLog:
PR c++/94775
* stor-layout.c (finalize_type_size): If we reset TYPE_USER_ALIGN in
the main variant, maybe reset it in its variants too.
* tree.c (check_base_type): Return true only if TYPE_USER_ALIGN match.
(check_aligned_type): Check if TYPE_USER_ALIGN match.
gcc/testsuite/ChangeLog:
PR c++/94775
* g++.dg/cpp0x/alignas19.C: New test.
* g++.dg/warn/Warray-bounds15.C: New test.
Diffstat (limited to 'gcc/tree.c')
-rw-r--r-- | gcc/tree.c | 4 |
1 files changed, 3 insertions, 1 deletions
@@ -6573,7 +6573,8 @@ check_base_type (const_tree cand, const_tree base) TYPE_ATTRIBUTES (base))) return false; /* Check alignment. */ - if (TYPE_ALIGN (cand) == TYPE_ALIGN (base)) + if (TYPE_ALIGN (cand) == TYPE_ALIGN (base) + && TYPE_USER_ALIGN (cand) == TYPE_USER_ALIGN (base)) return true; /* Atomic types increase minimal alignment. We must to do so as well or we get duplicated canonical types. See PR88686. */ @@ -6608,6 +6609,7 @@ check_aligned_type (const_tree cand, const_tree base, unsigned int align) && TYPE_CONTEXT (cand) == TYPE_CONTEXT (base) /* Check alignment. */ && TYPE_ALIGN (cand) == align + && TYPE_USER_ALIGN (cand) == TYPE_USER_ALIGN (base) && attribute_list_equal (TYPE_ATTRIBUTES (cand), TYPE_ATTRIBUTES (base)) && check_lang_type (cand, base)); |