Re: [jamboost] Re: /OPT:REF,ICF on linking command line in debug msvc build

From: Zbynek Winkler (zwin_at_[hidden])
Date: 2003-05-12 07:51:14

David Abrahams wrote:

>Vladimir Prus <ghost_at_[hidden]> writes:
> 
>
>>Zbynek Winkler wrote:
>> 
>>
>>>This is the command line used for final linking stage of my debug build:
>>>
>>>LINK /DEBUG /OPT:REF,ICF /subsystem:console 
>>>/out:"test\bin\msvc\debug\main-target-test\test.exe " 
>>>@"test\bin\msvc\debug\main-target-test\test.rsp"
>>>
>>>I am getting a warning:
>>>LINK : warning LNK4075: ignoring /EDITANDCONTINUE due to /OPT specification
>>>
>>>Why is there /OPT option even for debug build? Is that a bug or a feature?
>>> 
>>>
>>The msvc support was implemented by David Abrahams. Dave, can you comment on 
>>this issue?
>> 
>>
>
>Well, the docs say:
>
> The following linker options disable Edit and Continue. 
>
> Setting /OPT:REF, /OPT:ICF, or /INCREMENTAL:NO disables Edit
> and Continue with the following warning:
>
> LINK : warning LNK4075: ignoring /EDITANDCONTINUE due to /OPT
> specification
>
>So the warning is going to be there for some combination of
>optimizations whether we like it or not.
>
When we specify an optimization that disables edit-and-continue then we 
should not use the debug info that allows the edit-and-continue feature. 
That should get rid off the warning. The option for the compiler to 
enable E&C is /ZI. I think that /Zi should be used instead (Program 
Database). The equivalent for the linker should be /DEBUG /DEBUGTYPE:CV 
(according to the docs). After a while of experimenting with the linker 
my impression is that when you do not specify /DEBUGTYPE it defaults to 
(undocumented) /EDITANDCONTIUE option.

Different question is what the default should be. I am in the position 
of replacing *.dsp with Jamfiles so the best defaults for me are the 
defaults used in *.dsp. That includes default to enable "Edit and 
Continue". What is the current rule to decide what should be the default 
for release/debug builds on each platform?

The docs about the /OPT:REF,ICF also say:

If the /DEBUG option is specified, the default for /OPT changes from
REF* *to NOREF, and all functions are preserved in the image. To
override this default and optimize a debugging build, specify
/OPT:REF. The /OPT:REF option disables incremental linking.

So obviously the MS's default is not to optimize debugging build in any 
way unless told otherwise which seems reasonable to me.

Anyway, I think that saying <optimization>off should disable all 
optimizations (including linker) and that <optimization>off should be 
set for the default debug build. Why to include some optimization and 
some other not?

Zbynek

-- 
<zwin at robotika.cz>
http://zw.matfyz.cz/ http://robotika.cz/
Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic