On 05/05/11 19:35, Marsh Ray wrote: <snip>
So I'm interpreting that as "Can you give an example of an actual C++ program where the compiler does not emit the same code for references as the analogous code using plain pointers."
.... I played around with g++-4.6.0 and was not able to make it emit different code in the short time I'm willing to try. G++ seems to miss some opportunities for optimization of references, and seems to be smart about tracking pointer values.
There's this: struct A { int x; }; struct B { int y; }; struct C : A, B {}; C& f(B& b) { return static_cast<C&>(b); } C* g(B* b) { return static_cast<C*>(b); } which compiles to: 0000000000000000 <_Z1fR1B>: 0: 48 8d 47 fc lea -0x4(%rdi),%rax 4: c3 retq 0000000000000010 <_Z1gP1B>: 10: 48 8d 57 fc lea -0x4(%rdi),%rdx 14: 31 c0 xor %eax,%eax 16: 48 85 ff test %rdi,%rdi 19: 48 0f 45 c2 cmovne %rdx,%rax 1d: c3 retq The compiler doesn't have to do a null-check for the reference case, so it's shorter. John Bytheway