Thread local variables in betterC

[Blatnik]

On Sunday, 9 May 2021 at 22:55:41 UTC, Imperatorn wrote:
> Check the assembly

I already did, here's the "wrong" version when I only run `$ dmd 
-betterC -m64 test.d`:

```
Dump of file test.obj

main:
   push        rbp
   mov         rbp,rsp
   mov         rax,qword ptr gs:[58h]

   mov         rcx,qword ptr [rax]
   mov         edx,offset _D4test1ai
   mov         dword ptr [rcx+rdx],42

   xor         eax,eax
   pop         rbp
   ret
```

And here it is when I run `$ dmd -betterC -m64 -c test.d`:

```
Dump of file test.obj

main:
   push        rbp
   mov         rbp,rsp
   push        rbx
   mov         eax,dword ptr [_tls_index] <--------
   mov         rcx,qword ptr gs:[58h]

   mov         rdx,qword ptr [rcx+rax*8]
   mov         ebx,offset _D4test1ai
   mov         dword ptr [rdx+rbx],42

   xor         eax,eax
   pop         rbx
   rbp
   ret
```

So this just seems like some sort of compiler bug. It doesn't 
emit the TLS index retrieval unless you compile with `-c` and 
link separately.

Also, I've looked into this now, and thread locals _should_ work 
in -betterC as far as I can tell. There's no mention of them not 
working on https://dlang.org/spec/betterc.html, and if they 
really didn't work it would have been mentioned there in bold all 
caps. It would be pretty important to mention that `int a = 0;` 
doesn't work correctly.