On Monday, 25 November 2019 at 13:09:44 UTC, mipri wrote:
class C {
int x;
this(int n) { x = n; }
}
int heap() {
auto x = new C(2); // vgc: `new` causes a GC allocation
return x.x;
}
/+
int example.heap():
sub rsp, 8
mov edi, OFFSET FLAT:example.C.__Class
call _d_newclass
mov DWORD PTR [rax+16], 2
mov eax, 2
add rsp, 8
ret
+/
gdc assembly.
What about adding a new optimization pass to the compiler that
infers `scope` of each class instance `x` if it (and all it's
aliasings) are
- only passed to scope parameters of functions and
- doesn't escape into a global variable or via a return value
? I recall such as mechanism already exists for GC-allocated
dynamic arrays which, in release builds of ldc at least, are
replaced with stack-allocated arrays (if they are small enough).
Also, what happens if `C` doesn't fit on the stack? In that case
the compiler should allocate `C` using a deterministic allocator
via `malloc` or `mmap` and `free` or `munmap` the instance at the
end of `x`'s lifetime.
