add throw() exception specification to all non-throwing functions
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Key: STDCXX-998
URL: https://issues.apache.org/jira/browse/STDCXX-998
Project: C++ Standard Library
Issue Type: Improvement
Components: Build and Installation
Affects Versions: 4.2.1
Reporter: Martin Sebor
Priority: Critical
Fix For: 4.2.2
When a compiler cannot determine whether a function declared without an
explicit exception specification may throw an exception or not (e.g., because
the compiler/optimizer doesn't have access to the definition of the function)
it must assume that the function may throw and may need to generate suboptimal
code as a result.
Compilers often assume that even inline functions that can be proven not to
throw exceptions may throw unless they are declared with the empty exception
specification and generates suboptimal code as a result. For example, HP aCC 6
assumes that {{S::S()}} in the code below may throw
and fails to optimize the catch block away, generating object code 2.5 times
the size bigger than necessary. (Note that gcc 3.4 on IPF generates optimal
code in this case).
To help compilers generate optimal code we should make use of the empty
exception specification on all functions that cannot throw exceptions,
including those declared explicitly or implicitly {{inline}}.
{code}
#include <new>
struct S {
int i;
S () /* throw () */: i () { }
};
void uninit_fill (S *a, S *b)
{
S *p = a;
try {
for ( ; p != b; ++p)
new (p) S ();
}
catch (...) {
while (p-- != a)
p->~S ();
throw;
}
}
{code}
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