Link time optimization in D

[retard]

Mon, 31 May 2010 15:41:00 -0700, Walter Bright wrote:

> retard wrote:
>> Mon, 31 May 2010 18:23:18 +0200, Pelle wrote:
>> 
>>> On 05/31/2010 05:43 PM, retard wrote:
>>>> DMD is much slower than Sun Javac/Jvm 7, GNU GCC 4.5, and LLVM.
>>> For very special values of much, I suppose.
>> 
>> Polymorphic method calls, auto-vectorization, link-time optimization,
>> floating point performance, etc.
> 
> Link time optimization? Let's examine it:
> 
> https://lwn.net/Articles/387122/
> 
> "When source files are compiled and linked using -flto, GCC applies
> optimizations as if all the source code were in a single file. This
> allows GCC to perform more aggressive optimizations across files, such
> as inlining the body of a function from one file that is called from a
> different file, and propagating constants across files. In general, the
> LTO framework enables all the usual optimizations that work at a higher
> level than a single function to also work across files that are
> independently compiled."
> 
> D has had that for 8 years now, it's just done in the compiler instead
> of the linker. You can specify as many D source modules as you want on
> the command line to the compiler, and it will compile & optimizer &
> inline them all together and generate one object file.
> 
> Essentially, link time optimization is a hack to get around the language
> problem C/C++ have with their separate compilation model.
> 
> To say D code is slower because it lacks link-time optimization is a
> false supposition.

I thought the DMD's approach required sources for each module and GCC 
supported LTO even when only object / library files were provided.