Re: The D Programming Language

From:

"Mirek Fidler" <cxl@ntllib.org>

Newsgroups:

comp.lang.c++.moderated

Date:

27 Nov 2006 12:23:12 -0500

Message-ID:

<1164638220.349075.275720@l39g2000cwd.googlegroups.com>

Inlining a function doesn't necessarily imply replacing a reference type
with a value type.

The problem is, a compiler looks at a UDT from the lowest level
possible. It has *no idea* what that type is supposed to be; not a clue.
All it sees are the low level operations on it. Trying to infer
identities and high level operations from that is akin to handing an AI
engine a few identities and expecting it to construct all kinds of
useful theorems from them. It ain't gonna happen.

I am afraid my response might be considered a little bit offending, but
I have to ask:

Are we speaking about DMC++ here? :)

In reality, I see no reason why good compiler could not optimize out a
reference.

I have just checked with GCC4.1 / AMD64 (to reduce register pressure):

struct Foo {
    int a, b;
};

inline void Add(Foo& x, int q) { x.a += q; x.b += q; }

void Print(int); // just to force code generation

void main()
{
    Foo x;
    x.a = 10;
    x.b = 20;
    Add(x, rand());
    Print(x.a);
    Print(x.b);
}

and it produced this:

callq 0x4055b0 <rand@plt>
mov %eax,%ebx
lea 0xa(%rbx),%edi
callq 0x406038 <_Z5Printi>
lea 0x14(%rbx),%edi
callq 0x406038 <_Z5Printi>

Or maybe I misunderstood the problem?

Mirek

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