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author | Richard Biener <rguenther@suse.de> | 2023-02-23 11:56:17 +0100 |
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committer | Richard Biener <rguenther@suse.de> | 2023-02-24 16:41:36 +0100 |
commit | 2dd68cddbc745de2c4a4b4982673122716c8231c (patch) | |
tree | 2264d105a68d042dfa84ef637878e489323fcbe6 /gcc | |
parent | ef22c3e90b5010a5229e70907ad2087f774fdfc0 (diff) | |
download | gcc-2dd68cddbc745de2c4a4b4982673122716c8231c.zip gcc-2dd68cddbc745de2c4a4b4982673122716c8231c.tar.gz gcc-2dd68cddbc745de2c4a4b4982673122716c8231c.tar.bz2 |
Avoid default-initializing auto_vec<T, N> storage, fix vec<vl_embed>
The following avoids default-initializing auto_vec storage for
non-POD T since that's not what the allocated storage fallback
will do and it's also not expected for existing cases like
auto_vec<std::pair<unsigned, unsigned>, 64> elts;
which exist to optimize the allocation.
It also fixes the array accesses done by vec<vl_embed> to not
use its own m_vecdata member but instead access the container
provided storage via pointer arithmetic.
* vec.h (vec<T, A, vl_embed>::m_vecdata): Remove.
(vec<T, A, vl_embed>::m_vecpfx): Align as T to avoid
changing alignment of vec<T, A, vl_embed> and simplifying
address.
(vec<T, A, vl_embed>::address): Compute as this + 1.
(vec<T, A, vl_embed>::embedded_size): Use sizeof the
vector instead of the offset of the m_vecdata member.
(auto_vec<T, N>::m_data): Turn storage into
uninitialized unsigned char.
(auto_vec<T, N>::auto_vec): Allow allocation of one
stack member. Initialize m_vec in a special way to
avoid later stringop overflow diagnostics.
* vec.cc (test_auto_alias): New.
(vec_cc_tests): Call it.
Diffstat (limited to 'gcc')
-rw-r--r-- | gcc/vec.cc | 17 | ||||
-rw-r--r-- | gcc/vec.h | 31 |
2 files changed, 37 insertions, 11 deletions
@@ -568,6 +568,22 @@ test_auto_delete_vec () ASSERT_EQ (dtor_count, 2); } +/* Verify accesses to m_vecdata are done indirectly. */ + +static void +test_auto_alias () +{ + volatile int i = 1; + auto_vec<int, 8> v; + v.quick_grow (2); + v[0] = 1; + v[1] = 2; + int val; + for (int ix = i; v.iterate (ix, &val); ix++) + ASSERT_EQ (val, 2); + ASSERT_EQ (val, 0); +} + /* Run all of the selftests within this file. */ void @@ -587,6 +603,7 @@ vec_cc_tests () test_qsort (); test_reverse (); test_auto_delete_vec (); + test_auto_alias (); } } // namespace selftest @@ -586,8 +586,9 @@ public: unsigned allocated (void) const { return m_vecpfx.m_alloc; } unsigned length (void) const { return m_vecpfx.m_num; } bool is_empty (void) const { return m_vecpfx.m_num == 0; } - T *address (void) { return m_vecdata; } - const T *address (void) const { return m_vecdata; } + T *address (void) { return reinterpret_cast <T *> (this + 1); } + const T *address (void) const + { return reinterpret_cast <const T *> (this + 1); } T *begin () { return address (); } const T *begin () const { return address (); } T *end () { return address () + length (); } @@ -629,10 +630,10 @@ public: friend struct va_gc_atomic; friend struct va_heap; - /* FIXME - These fields should be private, but we need to cater to + /* FIXME - This field should be private, but we need to cater to compilers that have stricter notions of PODness for types. */ - vec_prefix m_vecpfx; - T m_vecdata[1]; + /* Align m_vecpfx to simplify address (). */ + alignas (T) alignas (vec_prefix) vec_prefix m_vecpfx; }; @@ -1315,7 +1316,7 @@ vec<T, A, vl_embed>::embedded_size (unsigned alloc) vec, vec_embedded>::type vec_stdlayout; static_assert (sizeof (vec_stdlayout) == sizeof (vec), ""); static_assert (alignof (vec_stdlayout) == alignof (vec), ""); - return offsetof (vec_stdlayout, m_vecdata) + alloc * sizeof (T); + return sizeof (vec_stdlayout) + alloc * sizeof (T); } @@ -1559,8 +1560,14 @@ class auto_vec : public vec<T, va_heap> public: auto_vec () { - m_auto.embedded_init (MAX (N, 2), 0, 1); - this->m_vec = &m_auto; + m_auto.embedded_init (N, 0, 1); + /* ??? Instead of initializing m_vec from &m_auto directly use an + expression that avoids refering to a specific member of 'this' + to derail the -Wstringop-overflow diagnostic code, avoiding + the impression that data accesses are supposed to be to the + m_auto member storage. */ + size_t off = (char *) &m_auto - (char *) this; + this->m_vec = (vec<T, va_heap, vl_embed> *) ((char *) this + off); } auto_vec (size_t s CXX_MEM_STAT_INFO) @@ -1571,8 +1578,10 @@ public: return; } - m_auto.embedded_init (MAX (N, 2), 0, 1); - this->m_vec = &m_auto; + m_auto.embedded_init (N, 0, 1); + /* ??? See above. */ + size_t off = (char *) &m_auto - (char *) this; + this->m_vec = (vec<T, va_heap, vl_embed> *) ((char *) this + off); } ~auto_vec () @@ -1590,7 +1599,7 @@ public: private: vec<T, va_heap, vl_embed> m_auto; - T m_data[MAX (N - 1, 1)]; + unsigned char m_data[sizeof (T) * N]; }; /* auto_vec is a sub class of vec whose storage is released when it is |