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

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.

                             -David

> -----Original Message-----
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of
David
> Greene via llvm-dev
> Sent: Friday, March 08, 2019 10:49 AM
> To: llvm-dev at lists.llvm.org
> Subject: [llvm-dev] [CMake] Re-configuring Debug and Release builds
> 
> 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 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.
--paulr
> 
>                              -David
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> llvm-dev at lists.llvm.org
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<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://llvm.org/docs/CMake.html#cmake-caches seems to imply that -D
options should override cache values, but it doesn't for
CMAKE_BUILD_TYPE.

                               -David