Are there any objections to this patch?
I find the function easier to parse in this form and it allows it to
be constexpr. Maybe more importantly, it determines the memory order
to be used by compare_exchange_xxx on failure so I think
__cmpexch_failure_order is a more descriptive name than
__calculate_memory_order.
* include/bits/atomic_base.h (__calculate_memory_order): Rename to...
(__cmpexch_failure_order): This, and rewrite as constexpr function.
(compare_exchange_strong, compare_exchange_weak): Use it.
* include/std/atomic (compare_exchange_strong, compare_exchange_weak):
Likewise.
Tested x86_64-linux.
Index: include/bits/atomic_base.h
===================================================================
--- include/bits/atomic_base.h (revision 181967)
+++ include/bits/atomic_base.h (working copy)
@@ -59,14 +59,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
memory_order_seq_cst
} memory_order;
- inline memory_order
- __calculate_memory_order(memory_order __m) noexcept
+ // Drop release ordering as per [atomics.types.operations.req]/21
+ constexpr memory_order
+ __cmpexch_failure_order(memory_order __m) noexcept
{
- const bool __cond1 = __m == memory_order_release;
- const bool __cond2 = __m == memory_order_acq_rel;
- memory_order __mo1(__cond1 ? memory_order_relaxed : __m);
- memory_order __mo2(__cond2 ? memory_order_acquire : __mo1);
- return __mo2;
+ return __m == memory_order_acq_rel ? memory_order_acquire
+ : __m == memory_order_release ? memory_order_relaxed : __m;
}
inline void
@@ -505,7 +503,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
memory_order __m = memory_order_seq_cst) noexcept
{
return compare_exchange_weak(__i1, __i2, __m,
- __calculate_memory_order(__m));
+ __cmpexch_failure_order(__m));
}
bool
@@ -513,7 +511,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
memory_order __m = memory_order_seq_cst) volatile noexcept
{
return compare_exchange_weak(__i1, __i2, __m,
- __calculate_memory_order(__m));
+ __cmpexch_failure_order(__m));
}
bool
@@ -544,7 +542,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
memory_order __m = memory_order_seq_cst) noexcept
{
return compare_exchange_strong(__i1, __i2, __m,
- __calculate_memory_order(__m));
+ __cmpexch_failure_order(__m));
}
bool
@@ -552,7 +550,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
memory_order __m = memory_order_seq_cst) volatile noexcept
{
return compare_exchange_strong(__i1, __i2, __m,
- __calculate_memory_order(__m));
+ __cmpexch_failure_order(__m));
}
__int_type
Index: include/std/atomic
===================================================================
--- include/std/atomic (revision 181967)
+++ include/std/atomic (working copy)
@@ -408,7 +408,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
memory_order __m = memory_order_seq_cst) noexcept
{
return compare_exchange_weak(__p1, __p2, __m,
- __calculate_memory_order(__m));
+ __cmpexch_failure_order(__m));
}
bool
@@ -416,7 +416,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
memory_order __m = memory_order_seq_cst) volatile noexcept
{
return compare_exchange_weak(__p1, __p2, __m,
- __calculate_memory_order(__m));
+ __cmpexch_failure_order(__m));
}
bool
@@ -435,7 +435,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
memory_order __m = memory_order_seq_cst) noexcept
{
return _M_b.compare_exchange_strong(__p1, __p2, __m,
- __calculate_memory_order(__m));
+ __cmpexch_failure_order(__m));
}
bool
@@ -443,7 +443,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
memory_order __m = memory_order_seq_cst) volatile noexcept
{
return _M_b.compare_exchange_strong(__p1, __p2, __m,
- __calculate_memory_order(__m));
+ __cmpexch_failure_order(__m));
}
__pointer_type
