[tree-ssa] Simplifying TARGET_EXPR

[Jason Merrill]

>>>>> "Nathan" == Nathan Sidwell <nathan@codesourcery.com> writes:

> Mark Mitchell wrote:
>> Maybe I'm developing an unhealthy paranoia.  On the one hand,
>> optimizing away more copy constructors is like optimizing away
>> more copies between scalars, and I'm all for having -O2 do more
>> of that!  On the other, copy constructor elision is observable
>> behavior in the program, and it's going to make it hard to do
>> debug, profile, and otherwise analyze your program if the number
>> of copy constructor calls changes when you optimize.

> I disagree. Alias analysis makes optimized broken programs hard
> to debug, I don't see why temporary elision is any different..
> Maybe have the elision separately disablable at -O2, but I think
> it should be permissable.

I agree.  Copy constructor calls are small change in debuggability of
optimized code.

Of course, we've never tried to optimize away more copy constructors after
inlining, so this is all theoretical...

Jason