Re: PATCH c++/19628 (take 2)

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

"Joseph S. Myers" <joseph@codesourcery.com> writes:

| On Sun, 30 Jan 2005, Roger Sayle wrote:
| 
| > One distinction that may be useful in this respect, might be something
| > like builtin.c's CALLED_AS_BUILT_IN macro.  This can be used to
| > distinguish built-in functions called as __builtin_foo from those
| > called as foo (or std::foo).  By using this, the C++ front-end
| > maintainers could choose to allow __builtin_fabs(0.0) to be a
| > compile-time constant, whilst retaining the usual semantics of
| > fabs(0.0).  __builtin_constant_p would then be just a special case.
| 
| The __builtin_nan*, __builtin_inf* and __builtin_huge_val* built-in 
| functions are documented as being usable in constant expressions (in the 
| case of nan*, only where they have string constant arguments).  However:
| 
| 1) These all only exist in the __builtin_ form, although it would now be 
| possible for the nan functions to become C99_BUILTIN instead of 
| GCC_BUILTIN since you fixed the bug that would have allowed calls to plain 
| "nan" as constant.
| 
| 2) These can only be used in arithmetic constant expressions, not integer 
| constant expressions, but whether something is or is not an arithmetic 
| constant expression is not particularly important in C++ since static 

except when used as template arguments.

There is some consensus and a proposal to allow "sufficiently simple"
functions (a.k.a. "constant-valued functions") to be considered as
constant expressions.

While Matt's patch is a step in that direction, I think we should
consider constant-valued functions  independently of this patch.

-- Gaby