Compiler flags when profiling a build

[Jacob Carlborg]

On Sunday, 25 October 2020 at 14:08:21 UTC, Per Nordlöw wrote:
> What flags do you feed to dmd/ldc when you profile a build?
>
> Do you initially
>
> - compile in debug or release mode?
> - activate inlining or not?
> - use dmd or ldc?
> - use any other alternatives not mentioned above?

For maximum performance you should compile with LDC and do the 
following:

* Enable optimizations: -O3
* Enable Link Time Optimizations (LTO): --flto=full
* Link against druntime and Phobos compiled for LTO: 
--defaultlib=druntime-ldc-lto,phobos2-ldc-lto
* Target your specific CPU instead of some generic CPU. This will 
enable SSE and other features that otherwise are disabled: 
-mcpu=native

* Depending on you're preferences, you might want to disable 
asserts, contracts and invariants and bounds checks in non- at safe 
functions: --release
* You can also control the bounds check in more details using 
this flag: --boundscheck

* For profiling I assume you want debug symbols as well: -g

--
/Jacob Carlborg