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Split and simplify partial_range check

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Rely on T.size() instead of distance(T.begin(), T.end()) to get the
container size.  Add a special case for C-style arrays with known size.

In some cases, gcc-4.9 fails to optimize distance(...) on an array<T, N>
of unknown base address, leading to a bogus compile failure.  Switching
the object to have a known address prevents the problem, but requires
changing the calling code.  Switch to using T.size(), which gcc seems to
get right.
This commit is contained in:
Kp 2015-02-01 23:07:18 +00:00
parent 36cd5404d4
commit 98afca20a9
1 changed files with 57 additions and 5 deletions
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62
common/include/partial_range.h
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@ -23,7 +23,9 @@ struct partial_range_t
m_begin(b), m_end(e)
{
}
__attribute_warn_unused_result
iterator begin() const { return m_begin; }
__attribute_warn_unused_result
iterator end() const { return m_end; }
bool empty() const __attribute_warn_unused_result
{
@ -74,6 +76,9 @@ struct base_partial_range_error_t : std::out_of_range
__attribute_warn_unused_result
static inline std::string prepare(const char (&file)[NF], unsigned line, const char (&estr)[NE], const char (&desc)[ND], unsigned long expr, const void *t, unsigned long d)
{
/* Round reporting into large buckets. Code size is more
* important than stack space.
*/
return prepare<((NF + NE + ND) | 0xff) + 1>(file + 0, line, estr, desc, expr, t, d);
}
};
@ -90,11 +95,36 @@ struct partial_range_error_t : base_partial_range_error_t
}
};
template <typename T, typename I, std::size_t NF, std::size_t NE>
static void check_partial_range(const char (&file)[NF], unsigned line, const char (&estr)[NE], T &t, I range_begin, I container_end, const std::size_t o, const std::size_t l)
namespace partial_range_detail
{
template <typename T, std::size_t NF, std::size_t NE>
static inline void check_range_bounds(const char (&file)[NF], unsigned line, const char (&estr)[NE], T &t, const std::size_t o, const std::size_t l, const std::size_t d)
{
using std::distance;
#ifdef DXX_HAVE_BUILTIN_CONSTANT_P
/*
* If EXPR and d are compile-time constant, and the (EXPR > d)
* branch is optimized out, then the expansion of
* PARTIAL_RANGE_COMPILE_CHECK_BOUND is optimized out, preventing
* the compile error.
*
* If EXPR and d are compile-time constant, and the (EXPR > d)
* branch is not optimized out, then this function is guaranteed to
* throw if it is ever called. In that case, the compile fails,
* since the program is guaranteed not to work as the programmer
* intends.
*
* If they are not compile-time constant, but the compiler can
* optimize based on constants, then it will optimize out the
* expansion of PARTIAL_RANGE_COMPILE_CHECK_BOUND, preventing the
* compile error. The function might throw on invalid inputs,
* including constant inputs that the compiler failed to recognize
* as compile-time constant.
*
* If the compiler cannot optimize based on the result of
* __builtin_constant_p (such as at -O0), then configure tests set
* !DXX_HAVE_BUILTIN_CONSTANT_P and the macro expands to nothing.
*/
#define PARTIAL_RANGE_COMPILE_CHECK_BOUND(EXPR,S) \
(__builtin_constant_p(EXPR) && __builtin_constant_p(d) && (DXX_ALWAYS_ERROR_FUNCTION(partial_range_will_always_throw, S " will always throw"), 0))
#else
@ -104,22 +134,44 @@ static void check_partial_range(const char (&file)[NF], unsigned line, const cha
if (EXPR > d) \
((void)(PARTIAL_RANGE_COMPILE_CHECK_BOUND(EXPR,S))), \
partial_range_error_t<const T>::report(file, line, estr, S, EXPR, t, d)
size_t d = distance(range_begin, container_end);
PARTIAL_RANGE_CHECK_BOUND(o, "begin");
PARTIAL_RANGE_CHECK_BOUND(l, "end");
#undef PARTIAL_RANGE_CHECK_BOUND
#undef PARTIAL_RANGE_COMPILE_CHECK_BOUND
}
/* C arrays lack a size method, but have a constant size */
template <typename T, std::size_t NF, std::size_t NE, std::size_t d>
static inline void check_partial_range(const char (&file)[NF], unsigned line, const char (&estr)[NE], T (&t)[d], const std::size_t o, const std::size_t l)
{
check_range_bounds(file, line, estr, t, o, l, d);
}
template <typename T, std::size_t NF, std::size_t NE>
static inline void check_partial_range(const char (&file)[NF], unsigned line, const char (&estr)[NE], T &t, const std::size_t o, const std::size_t l)
{
check_range_bounds(file, line, estr, t, o, l, t.size());
}
}
template <typename I>
__attribute_warn_unused_result
static inline partial_range_t<I> unchecked_partial_range(I range_begin, const std::size_t o, const std::size_t l, tt::true_type)
{
#ifdef DXX_HAVE_BUILTIN_CONSTANT_P
/* Compile-time only check. Runtime handles (o > l) correctly, and
* it can happen in a correct program. If it is guaranteed to
* happen, then the range is always empty, which likely indicates a
* bug.
*/
if (__builtin_constant_p(!(o < l)) && !(o < l))
DXX_ALWAYS_ERROR_FUNCTION(partial_range_is_always_empty, "offset never less than length");
#endif
auto range_end = range_begin;
/* Use <= so that (o == 0) makes the expression always-true, so the
* compiler will optimize out the test.
*/
if (o <= l)
{
using std::advance;
@ -152,8 +204,8 @@ template <typename T, typename UO, typename UL, std::size_t NF, std::size_t NE,
__attribute_warn_unused_result
static inline partial_range_t<I> partial_range(const char (&file)[NF], unsigned line, const char (&estr)[NE], T &t, const UO &o, const UL &l)
{
partial_range_detail::check_partial_range(file, line, estr, t, o, l);
auto range_begin = begin(t);
check_partial_range(file, line, estr, t, range_begin, end(t), o, l);
return unchecked_partial_range<I, UO, UL>(range_begin, o, l);
}