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authorRichard Biener <rguenther@suse.de>2023-02-23 11:56:17 +0100
committerRichard Biener <rguenther@suse.de>2023-02-24 16:41:36 +0100
commit2dd68cddbc745de2c4a4b4982673122716c8231c (patch)
tree2264d105a68d042dfa84ef637878e489323fcbe6 /gcc
parentef22c3e90b5010a5229e70907ad2087f774fdfc0 (diff)
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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.cc17
-rw-r--r--gcc/vec.h31
2 files changed, 37 insertions, 11 deletions
diff --git a/gcc/vec.cc b/gcc/vec.cc
index 511e6df..2128f66 100644
--- a/gcc/vec.cc
+++ b/gcc/vec.cc
@@ -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
diff --git a/gcc/vec.h b/gcc/vec.h
index 2b36f06..3691891 100644
--- a/gcc/vec.h
+++ b/gcc/vec.h
@@ -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