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From: Cédric Venet (cedric.venet_at_[hidden])
Date: 2007-08-11 11:00:23

> > Do you have any evidence of this? I've read somewhere that Visual 8
> > does something like this, but I hope this is not the COMDAT folding
> option.
> > This redundant machine code erasing is performed by the linker, the
> > code is still instantiated at compile time, so we are not going to
> > save much compilation time.
> No, it's not some new esoteric thing: Given some code like
> template<typename T> struct X
> { /* code inside that only uses T* */ }
> the compiler can determine that an incomplete type suffices for 'T' and
> that instances for any 'T' are interchangeable.

I tried with std::vector<type*> (cf joined source file) and it is the COMDAT
folding which do the work:
Without: 36ko
With: 28ko

(the others options by default, in particular Win98 optimization is on
bumping the size)

The COMDAT folding is on by default.

I don't know how much this affect the compile time, but at least it should
greatly reduce the code bloat.
It could break some code:

template< class T >
         void testFct(T t) {
                std::cout << t << std::endl;
                 std::cout << "ptr1: " << static_cast< void(*)(t1*)
>(&testFct<t1*>) << std::endl;
                 std::cout << "ptr2: " << static_cast< void(*)(t2*)
>(&testFct<t2*>) << std::endl;

with COMDAT folding the function address are the same (not without)

(using VS8)


Cédric Venet

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