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digitalmars.D.learn - Empty struct, any runtime cost?

reply "SimonN" <eiderdaus gmail.com> writes:
Hi,

in a release-like build, I'm using the tharsis profiler, which is 
a
frame-based profiler. Zone is a RAII struct that measures how 
long its own
lifetime is.

     with (Zone(my_profiler, "zone name to appear in output")) {
         do_expensive_work();
         do_some_more_work();
     }
     // Zone goes out of scope here

I would like to use this code without modification in a release 
build
without profiling. I would rather not put version statements 
everywhere.
I have only one version statement in a single file that's 
included by
all files doing profiling:

     version (release_with_profiling) {
         public import tharsis.prof;
     }
     else {
         class Profiler { }
         struct Zone { this(Profiler, string) { } }
     }

Using that, the first code sample compiles in the non-profiling 
build,
where Zone is an empty struct.

*   Will the empty struct get optimized away completely by the 
compiler,
     at least if we pass -O -inline? I'd really like that, I have
     profiling code in several inner loops.

*   If not, what other approach could be usable to keep 
boilerplate in
     most source files to a minimum?

-- Simon
Aug 19 2015
next sibling parent "SimonN" <eiderdaus gmail.com> writes:
On Wednesday, 19 August 2015 at 09:54:33 UTC, SimonN wrote:

 Hi,


I've found this thread (Theoretical best practises):
http://forum.dlang.org/thread/codmadrwuyqxbklmuoiy forum.dlang.org

My goal is the same; I'm only more wary of putting debug/version
everywhere. If the empty struct isn't optimized away fully,
I'd still be up for what's recommended in that thread.

-- Simon
Aug 19 2015
prev sibling parent reply "Nicholas Wilson" <iamthewilsonator hotmail.com> writes:
On Wednesday, 19 August 2015 at 09:54:33 UTC, SimonN wrote:

 Hi,

 in a release-like build, I'm using the tharsis profiler, which 
 is a
 frame-based profiler. Zone is a RAII struct that measures how 
 long its own
 lifetime is.

     with (Zone(my_profiler, "zone name to appear in output")) {
         do_expensive_work();
         do_some_more_work();
     }
     // Zone goes out of scope here

 I would like to use this code without modification in a release 
 build
 without profiling. I would rather not put version statements 
 everywhere.
 I have only one version statement in a single file that's 
 included by
 all files doing profiling:

     version (release_with_profiling) {
         public import tharsis.prof;
     }
     else {
         class Profiler { }
         struct Zone { this(Profiler, string) { } }
     }

 Using that, the first code sample compiles in the non-profiling 
 build,
 where Zone is an empty struct.

 *   Will the empty struct get optimized away completely by the 
 compiler,
     at least if we pass -O -inline? I'd really like that, I have
     profiling code in several inner loops.


I'd be surprised if it didn't, but you can always check the 
disassembly.
If for some reason either the compiler doesn't remove it (it never
removes classes btw but not sure about structs) or the linker
doesn't discard it you can try -gcsections ( or w/e its called ).


 *   If not, what other approach could be usable to keep 
 boilerplate in
     most source files to a minimum?

 -- Simon
Aug 19 2015
parent Jacob Carlborg <doob me.com> writes:
On 2015-08-19 16:05, Nicholas Wilson wrote:


 I'd be surprised if it didn't, but you can always check the disassembly.
 If for some reason either the compiler doesn't remove it (it never
 removes classes btw but not sure about structs) or the linker
 doesn't discard it you can try -gcsections ( or w/e its called ).


I think the compiler still generates typeinfo for it.

-- 
/Jacob Carlborg
Aug 19 2015