gdc for rv32&64

[jfondren]

On Wednesday, 18 August 2021 at 08:09:36 UTC, Iain Buclaw wrote:
> On Wednesday, 18 August 2021 at 07:08:09 UTC, Mahdi wrote:
>>
>> A helloworld program on the X86_64-pc-linux-gnu platform 
>> contains 40 lines of assembly code or on the ARM 
>> (aarch64-linux-gnu) platform only 34 lines of assembly code, 
>> but on the risc-v(riscv64-unknow-gnu-linux) platform contains 
>> 871 lines of code on the explore.dgnu.org site!
>>
>> I'm concerned that this will affect the performance of the 
>> risc-v platform.
>
> A Phobos helloworld is over 1000 lines of assembly on both 
> x86_64 and ARM64.  My guess is that Compiler Explorer isn't 
> smart enough to filter RISC-V assembly in the same way as ARM 
> or X86.

This can be confirmed locally with objdump, to reveal a bunch of 
code that's filtered out by default:

```
$ cat hello.d
void main() {
     import std.stdio : writeln;
     writeln("Hello, world!");
}
$ gdc hello.d
$ objdump -dwr --no-show-raw-insn a.out | grep -m1 isValidDchar | 
ddemangle
    3179a:	call   6b870 <pure nothrow @nogc @safe bool 
std.utf.isValidDchar(dchar)>
```

You can also confirm it the Compiler Explorer by opening the 
Filter menu, below the compiler selection and "Compiler 
options..." input, and unchecking the 'Directives' filter.