[LLVMdev] compiler-rt CMake build

[Alexey Samsonov]

Hi Brad,

Thanks for investigating this. Do you think it makes sense to land my
ExternalProject_Add patch
so that others can experiment with it? I can add quit with a
fatal_error/warning if the build tree rules
are generated with Ninja. However, there is a problem with Unix Makefiles
as well: parallelism doesn't
work when I run "make check-compiler-rt -j8" in the original build tree,
presumably because we call
"cd /path/to/compiler-rt/build/tree && make check-all" there.


On Tue, Feb 25, 2014 at 7:02 PM, Brad King <brad.king at kitware.com> wrote:

> On 02/25/2014 03:28 AM, Alexey Samsonov wrote:
> > Then I run
> > $ ninja compiler-rt
> > twice. The first run builds the libraries, the second shows only:
> > "ninja: no work to do." message.
>
> I'm able to reproduce that, thanks.  This is a subtle interaction
> between always-out-of-date rules and order-only dependencies.
>
> The problem is that the build.ninja file has the rule:
>
>  build
> projects/compiler-rt/src/compiler-rt-stamp/compiler-rt-force-reconfigure:
> phony || bin/clang bin/llvm-config
>
> to express the always-out-of-date force-reconfigure rule.  The Ninja
> documentation says:
>
>  "If a phony build statement is written without any dependencies,
>   the target will be considered out of date if it does not exist."
>
> However, the rule has dependencies because the Ninja generator implements
> add_dependencies by adding order-only dependencies to every individual
> rule in the dependent target on all dependencies.
>
> It looks like the Ninja generator needs to write a rule is always out
> of date but still has order-only dependencies.  I think this will work:
>
>  build
> projects/compiler-rt/src/compiler-rt-stamp/compiler-rt-force-reconfigure:
> phony | always || bin/clang bin/llvm-config
>  build always: phony
>
> I've recorded this issue in the CMake issue tracker:
>
>  http://www.cmake.org/Bug/view.php?id=14771
>
> -Brad
>



-- 
Alexey Samsonov, MSK
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