llvm dev - Feb 2014 - [LLVMdev] compiler-rt CMake build

On Fri, Feb 21, 2014 at 7:31 PM, Brad King <brad.king at kitware.com>
wrote:
> On 02/21/2014 09:49 AM, Alexey Samsonov wrote:
> > 1) Looks like "DEPENDS" option is just broken
> > I use cmake 2.8.10.2.
>
> Dependencies on normal targets were accidentally broken in 2.8.9 and
> later fixed in 2.8.11 (along with a test case to keep it working):
>
>  http://www.cmake.org/Bug/view.php?id=13849
>  http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=c0f1af92
>
> > if I then change the Clang sources, and re-run "make
compiler-rt",
> > Clang is re-built, but compiler-rt is *not* re-configured or re-built
> [snip]
> > even if I modify *sources* under projects/compiler-rt
> > it doesn't re-build the compiler-rt libraries.
>
> ExternalProject was originally designed for two purposes:
>
> * Build third-party dependences on which local development will
>   not be done
>
> * Manage a "superbuild" project that has no binaries of its own
>   but has a bunch of ExternalProject_Add calls to drive set up
>   of a bunch of build trees.  Local development then occurs in
>   each tree manually.
>
> Using ExternalProject for a recursive-make-like structure was
> only later proposed as a use case.  In order to make the build
> step always run you need to make it depend on an extra step that
> is always out of date:
>
> ExternalProject_Add_Step(compiler-rt always-build
>   COMMENT "Always building MyCOnly..."
>   DEPENDERS build
>   ALWAYS 1
>   )
>
Great, thanks for suggestion! We can even use "DEPENDERS configure"
instead
of "DEPENDERS build" here.

And we'd better "clobber" the compiler-rt build tree if any of the
dependencies change (we need to rebuild
every compiler-rt source from scratch if clang has changed).

I will also try to add support for running tests in compiler-rt build tree.
I think this can be achieved by smth. like:
add_custom_target(check-compiler-rt
  COMMAND ${CMAKE_BUILD_TOOL} check-all
  DEPENDS compiler-rt
  WORKING_DIRECTORY ${COMPILER_RT_BUILD_DIR})

> -Brad
>
>
-- 
Alexey Samsonov, MSK
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On 02/21/2014 11:20 AM, Alexey Samsonov wrote:
> We can even use "DEPENDERS configure" instead of "DEPENDERS
build" here.
Just "build" should be sufficient because the generated build system
in compiler-rt knows how to re-run CMake if any of the inputs have
changed.  This is just as you do not need to re-run "cmake ." by hand
after editing CMakeLists.txt and can just type "make".

-Brad

On Fri, Feb 21, 2014 at 9:03 PM, Brad King <brad.king at kitware.com>
wrote:
> On 02/21/2014 11:20 AM, Alexey Samsonov wrote:
> > We can even use "DEPENDERS configure" instead of
"DEPENDERS build" here.
>
> Just "build" should be sufficient because the generated build
system
> in compiler-rt knows how to re-run CMake if any of the inputs have
> changed.  This is just as you do not need to re-run "cmake ." by
hand
> after editing CMakeLists.txt and can just type "make".
>
I am not convinced. Suppose LLVMConfig.cmake (which we read in standalone
compiler-rt build system) has changed.
Then we should re-run cmake for standalone compiler-rt even though none of
its cmake or source files was changed.

Could you take a look if http://llvm-reviews.chandlerc.com/D2868 looks
reasonable?

>
> -Brad
>
>

-- 
Alexey Samsonov, MSK
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