[llvm-dev] Ninja behavior that befuddles me

[Robinson, Paul via llvm-dev]

> -----Original Message-----
> From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Paul C.
> Anagnostopoulos via llvm-dev
> Sent: Wednesday, August 12, 2020 8:48 AM
> To: Michael Kruse <llvmdev at meinersbur.de>
> Cc: llvm-dev <llvm-dev at lists.llvm.org>
> Subject: Re: [llvm-dev] Ninja behavior that befuddles me
> 
> I'm a total newbie as far as CMake and Ninja are concerned. How do I force
> Ninja to build the target .inc files? I'm working on TableGen, so my
> changes to the executable may indeed change the output files. I want to be
> sure they did not, in fact, change.
> 
> Should I just touch all the .td files?

That's the traditional method for forcing something to rebuild.
Note the .td rules actually create the new .inc file "on the side"
and only overwrite the target .inc file itself if the new file
does not compare equal, so you could look at the .inc timestamps
after the build to determine whether any have been updated.

If you're especially worried, you could rename all the .inc files
in the build tree, which will cause all new .inc files to be
created using your modified tablegen; then you can do your own
diffs and verify no changes in the generated files.
This method will of course cause everything that depends on the
.inc files to be rebuilt, so the test build will take much longer,
but it would provide that little extra warm-fuzzy feeling.
--paulr