[GSoC 2019] Interested in Baremetal D Runtime and project ideas

[Stefanos Baziotis]

On Wednesday, 10 April 2019 at 00:05:16 UTC, Mike Franklin wrote:
> Yes, looking at the asm would be a good way to confirm it.  I 
> haven't done that, and I'm mostly relying on rumor, but here's 
> some evidence:  
> https://github.com/dlang/dmd/blob/e3cb9363bff55170624667fb819289aceccdc90d/src/dmd/backend/cod2.d#L3395-L3399

Yes, it's interesting. Well, unfortunately it needs a lot of time 
to understand
the backend enough to track whether it actually replaces it.

However, I made a simple test case:

import core.stdc.string;
extern(C) void main() {
	int a = 5;
	int b = 5;
	memcmp(&a, &b, int.sizeof);
}

which is a test case that should definitely be inlined.

Compiled with -betterC -g -O -release -inline, there is an actual 
call:
lea    rsi,[rbp-0x4]
lea    rdi,[rbp-0x8]
call   0x400640 <memcmp at plt>

and the code inside the call is what I would expect for a full 
memcmp.

I used -betterC because it makes smaller executables and makes it 
easy to
inspect on GDB. Maybe without it, dmd inlines it in some way 
although I doubt it.
Also, maybe LDC and GDC do something clever, but I don't have 
available right now either
of them.