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tree: Don't reuse types if TYPE_USER_ALIGN differ [PR94775]

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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.

	PR c++/94775
	* tree.c (check_base_type): Return true only if TYPE_USER_ALIGN match.
	(check_aligned_type): Check if TYPE_USER_ALIGN match.

	* g++.dg/warn/Warray-bounds-10.C: New test.
This commit is contained in:
Marek Polacek 2020-04-29 15:36:35 -04:00
parent cd4b685279
commit 6318fe7739
4 changed files with 54 additions and 1 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,9 @@
2020-04-30 Marek Polacek <polacek@redhat.com>
PR c++/94775
* tree.c (check_base_type): Return true only if TYPE_USER_ALIGN match.
(check_aligned_type): Check if TYPE_USER_ALIGN match.
2020-04-30 Kyrylo Tkachov <kyrylo.tkachov@arm.com>
* config/aarch64/aarch64.h (TARGET_OUTLINE_ATOMICS): Define.

5
gcc/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2020-04-30 Marek Polacek <polacek@redhat.com>
PR c++/94775
* g++.dg/warn/Warray-bounds-10.C: New test.
2020-04-30 Szabolcs Nagy <szabolcs.nagy@arm.com>
PR target/94748

40
gcc/testsuite/g++.dg/warn/Warray-bounds-10.C Normal file
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@ -0,0 +1,40 @@
// PR c++/94775
// { dg-do compile { target c++14 } }
// { dg-options "-O2 -Warray-bounds" }
template <typename> using a = int;
template <bool, typename, typename> using b = int;
typedef char d;
template <long> using e = int;
template <int f, int q> struct h { using i = b<q, a<e<f>>, e<f>>; };
template <long f, bool g> using j = typename h<f, g>::i;
long ab, k, aj;
const d l[]{};
class m {
public:
m(int);
};
class n {
void ad() const;
template <class ae> void o(long) const {
using c __attribute__((aligned(1))) = const ae;
}
long p;
template <class, class>
auto s(unsigned long, unsigned long, unsigned long, unsigned long) const;
template <bool = false> auto q(unsigned long, unsigned long) const;
};
template <class, class>
auto n::s(unsigned long, unsigned long, unsigned long, unsigned long t) const {
o<d>(p);
return t;
}
template <bool g> auto n::q(unsigned long p1, unsigned long p2) const {
using r = j<4, false>;
using ai = j<4, g>;
return s<ai, r>(ab, k, p1, p2);
}
void n::ad() const {
long f(l[aj]); // { dg-warning "outside array bounds" }
m(q(8, f));
}

4
gcc/tree.c
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@ -6493,7 +6493,8 @@ 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. */
@ -6528,6 +6529,7 @@ 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));