LDC2 with -fxray-instrument

[Johan Engelen]

On Monday, 21 January 2019 at 14:36:15 UTC, Márcio Martins wrote:
> On Thursday, 17 January 2019 at 00:11:10 UTC, Johan Engelen 
> wrote:
>>
>> OK, got it :-) LLVM 7 changed things a little, so it's broken 
>> with LDC 1.13  [*].
>>
>> For now, you can use LDC 1.12 (LLVM 6). You also have to add 
>> `-L-lstdc++` as compiler flag. So with LDC 1.12, Linux, and 
>> this commandline things work for me:
>> ```
>> ldc2 -fxray-instrument -fxray-instruction-threshold=1 
>> xraytest.d -L-lstdc++
>> XRAY_OPTIONS="patch_premain=true xray_mode=xray-basic 
>> verbosity=1" xraytest
>> ```
>>
>> Happy testing,
>>   Johan
>>
>> [*] XRay was split into several libraries, and we only 
>> copy+link with one of them. You can make things work by 
>> downloading the libs and linking with them.
>
> Great! Does it mean it will be fixed in next LDC release? :)

Yes: https://github.com/ldc-developers/ldc/pull/2965

> I also played a bit with -finstrument-functions and it works 
> fine for tools like uftrace... However, if you define your own 
> __cyg_profile_func_* functions, it won't work (or be useful), 
> because there is no way to disable instrumenting on these 
> __cyg_profile_func_* functions, so you can imagine what 
> happens. I tried @llvmAttr("no_instrument_function"), 
> supposedly the GCC compatible way to disable instrumentation on 
> these, but it doesn't make a difference.

You need:  pragma(LDC_profile_instr, false), e.g.:
```
pragma(LDC_profile_instr, false)
void fun () { ... }
``

> There are few LLVM settings that will make this useful:
> - https://reviews.llvm.org/D40276
> - https://reviews.llvm.org/D39331 (which enables instrumenting 
> after inlining, which is more useful in my use case)
> - https://reviews.llvm.org/D37622 (is has not been merged yet, 
> but necessary, to be able to conveniently call library 
> functions from within the hooks)

These are not too hard to implement in LDC. Whoever is interested 
in working on it, here are some pointers in addition to the LLVM 
links:
https://github.com/ldc-developers/ldc/issues/2466
https://github.com/ldc-developers/ldc/pull/1845/files

-Johan