[llvm-commits] [PATCH] Teach CMake to only touch tablegen-generated files if anything actually changed.

[Óscar Fuentes]

Frits van Bommel <fvbommel at gmail.com>
writes:

> I noticed the CMake build doesn't leave tablegen-generated files
> untouched if they are regenerated with the same contents[1]. The
> attached patch should fix that.
> This can save a lot of compilation if e.g. libLLVMSystem.a changed,
> causing the tblgen executable to be relinked without changing anything
> in the generated code. Especially clang seems heavily affected,
> probably due to the diagnostics tables.

Thanks. Applied in r117102.

IIRC a similar approach had problems in Windows: nmake (or was it
mingw32-make?) executed tablegen every time, as it considered the
resulting file always out of date.

This was a long time ago and since the build (and cmake) changed, so
let's try again.

[snip]