Overhead of DIP1036

[Walter Bright]

On 1/9/2024 12:45 AM, Alexandru Ermicioi wrote:
> If that's the case, then 1036 wins imho, by simple thing of not doing any 
> parsing of format string.

Consider the overhead 1036 has by comparing it with plain writeln or writefln:

```
void test(int baz)
{
     writeln(i"$(baz + 4)");
     writeln(baz + 5);
     writefln("%d", baz + 6);
}
```

Generated code:

0000:   55                       push      RBP
0001:   48 8B EC                 mov       RBP,RSP
0004:   48 83 EC 20              sub       RSP,020h
0008:   48 89 5D E8              mov       -018h[RBP],RBX

000c:   89 7D F8                 mov       -8[RBP],EDI          // baz
000f:   48 83 EC 08              sub       RSP,8
0013:   31 C0                    xor       EAX,EAX
0015:   88 45 F0                 mov       -010h[RBP],AL
0018:   48 8D 75 F0              lea       RSI,-010h[RBP]
001c:   FF 36                    push      dword ptr [RSI]      // header
001e:   88 45 F1                 mov       -0Fh[RBP],AL
0021:   48 8D 5D F1              lea       RBX,-0Fh[RBP]
0025:   FF 33                    push      dword ptr [RBX]      // 
expression!"baz + 4"
0027:   8D 7F 04                 lea       EDI,4[RDI]           // baz + 4
002a:   88 45 F2                 mov       -0Eh[RBP],AL
002d:   48 8D 75 F2              lea       RSI,-0Eh[RBP]
0031:   FF 36                    push      dword ptr [RSI]      // footer
0033:   E8 00 00 00 00           call      writeln

0038:   48 83 C4 20              add       RSP,020h
003c:   8B 45 F8                 mov       EAX,-8[RBP]
003f:   8D 78 05                 lea       EDI,5[RAX]           // baz + 5
0042:   E8 00 00 00 00           call      writeln

0047:   BA 00 00 00 00           mov       EDX,0                // "%d".ptr
004c:   BE 02 00 00 00           mov       ESI,2                // "%d".length
0051:   8B 4D F8                 mov       ECX,-8[RBP]
0054:   8D 79 06                 lea       EDI,6[RCX]           // baz + 6
0057:   E8 00 00 00 00           call      writefln

005c:   48 8B 5D E8              mov       RBX,-018h[RBP]
0060:   C9                       leave
0061:   C3                       ret

With the istring, there are 4 calls to struct member functions that just return 
null.
This can't be good for performance or program size.
We can compute the number of arguments passed to the function:

istring: 1 + 3 * <number of arguments> + 1 + 1  (*)
writeln: <number of arguments>
writefln: 1 + <number of arguments>

(*) includes string literals before, between, and after arguments