llvm dev - Mar 2019 - [CMake] Re-configuring Debug and Release builds

I'm unable to repro this – configuring once and then reconfiguring with a
different -DCMAKE_BUILD_TYPE= does the right thing for me. What's your exact
invocation?

If you're setting it from a cache file, you'll need to use FORCE in the
set in your cache file to override any existing cache setting.

On 3/8/19, 1:18 PM, "llvm-dev on behalf of David Greene via llvm-dev"
<llvm-dev-bounces at lists.llvm.org on behalf of llvm-dev at
lists.llvm.org> wrote:

    <paul.robinson at sony.com> writes:
    
    >> If I've configured a Release build, build it and then go back
and re-run
    >> cmake with -DCMAKE_BUILD_TYPE=Debug (and nothing else changed),
almost
    >> nothing gets rebuilt when I try to build.  Is this expected?  I
know I
    >> can edit CMakeCache.txt directly and trigger an essentially full
    >> rebuild.
    >
    > IME rerunning CMake with new options really does nothing;
CMakeCache.txt
    > appears to override the command line, which is not intuitive but seems
    > to be how it actually works.
    
    I thought so too at first, except changing LLVM_TARGETS_TO_BUILD when
    re-running CMake does indeed cause any new targets to be built.  So it
    can't be the case that the cache overrides everything.
    
    > I would hope that this is not a choice made by the LLVM project but a
    > bug/feature of CMake itself.  But I haven't ever had the energy to 
    > pursue it.
    
   
https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_docs_CMake.html-23cmake-2Dcaches&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=QX_nCpK2peaty_XOC8I0mM2FCcsrB0u93ckBWasLzfU&s=krJ8pnxDwobl6hQ3IB_hpM54u0pvD5MU-Ft5l6EL__4&e=
seems to imply that -D
    options should override cache values, but it doesn't for
    CMAKE_BUILD_TYPE.
    
                                   -David
    _______________________________________________
    LLVM Developers mailing list
    llvm-dev at lists.llvm.org
   
https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Ddev&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=QX_nCpK2peaty_XOC8I0mM2FCcsrB0u93ckBWasLzfU&s=J_T6_Sw0gdNOhChuI3RLRB-hUzsFpXWROa6KhwYK1T0&e=

Whether or not reconfiguring changing `CMAKE_BUILD_TYPE` does anything remotely
like what you want depends on which generator you use. It will result in full
rebuilds if you are using Ninja, but not Unix Makefiles. This is because Ninja
treats the command that generates the output as a dependency of the output.

That said in some environments the CMAKE_BUILD_TYPE can impact the values of
other cache variables that result from checks for libraries, headers, and
symbols. Those cache variables may not be updated in the re-run, which could
result in the build not doing what you expect.

In general many of the CMAKE_* variables like CMAKE_BUILD_TYPE and
CMAKE_<LANG>_COMPILER, cannot be safely changed without a full
re-configure, so I'd advise caution.

-Chris
> On Mar 8, 2019, at 1:22 PM, Shoaib Meenai via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> I'm unable to repro this – configuring once and then reconfiguring with
a different -DCMAKE_BUILD_TYPE= does the right thing for me. What's your
exact invocation?
> 
> If you're setting it from a cache file, you'll need to use FORCE in
the set in your cache file to override any existing cache setting.
> 
> On 3/8/19, 1:18 PM, "llvm-dev on behalf of David Greene via
llvm-dev" <llvm-dev-bounces at lists.llvm.org on behalf of llvm-dev at
lists.llvm.org> wrote:
> 
>    <paul.robinson at sony.com> writes:
> 
>>> If I've configured a Release build, build it and then go back
and re-run
>>> cmake with -DCMAKE_BUILD_TYPE=Debug (and nothing else changed),
almost
>>> nothing gets rebuilt when I try to build.  Is this expected?  I
know I
>>> can edit CMakeCache.txt directly and trigger an essentially full
>>> rebuild.
>> 
>> IME rerunning CMake with new options really does nothing;
CMakeCache.txt
>> appears to override the command line, which is not intuitive but seems
>> to be how it actually works.
> 
>    I thought so too at first, except changing LLVM_TARGETS_TO_BUILD when
>    re-running CMake does indeed cause any new targets to be built.  So it
>    can't be the case that the cache overrides everything.
> 
>> I would hope that this is not a choice made by the LLVM project but a
>> bug/feature of CMake itself.  But I haven't ever had the energy to 
>> pursue it.
> 
>   
https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_docs_CMake.html-23cmake-2Dcaches&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=QX_nCpK2peaty_XOC8I0mM2FCcsrB0u93ckBWasLzfU&s=krJ8pnxDwobl6hQ3IB_hpM54u0pvD5MU-Ft5l6EL__4&e=
seems to imply that -D
>    options should override cache values, but it doesn't for
>    CMAKE_BUILD_TYPE.
> 
>                                   -David
>    _______________________________________________
>    LLVM Developers mailing list
>    llvm-dev at lists.llvm.org
>   
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> 
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