[llvm-dev] TargetSelect.h and layering

David Blaikie via llvm-dev llvm-dev at lists.llvm.org
Tue Nov 28 11:23:47 PST 2017

Alternatively we can really say this header is a textual header - it's
included generally only once in a whole program, the functions are called
only once, etc. Though that does seem a little unfortunate on principle but
not much practical problem with it, I think. It'd be nice in theory to be
able to depend on the right library, have that bring in the right
dependencies, etc.

On Tue, Nov 28, 2017 at 11:15 AM David Blaikie <dblaikie at gmail.com> wrote:

> So, I'm setting about trying to fix the layering of TargetSelect.h (&
> TargetRegistry.h, but haven't really got to its issues yet).
> The issues can be demonstrated fairly plainly by moving any/all of
> TargetSelect.h's functions out of line. Pretty much all programs in LLVM
> fail to link because libSupport doesn't actually depend on all the targets,
> quite the opposite in fact.
> So, I set about creating a libLLVMAllTargets (for want of any better
> name/as a straw man) & wherever LLVM_TARGETS_TO_BUILD was listed in a
> CMakeLists.txt LLVM_LINK_COMPONENTS, I'd add in a dependence on AllTargets
> (& I moved all the function definitions in TargetSelect.h out of line to
> flush out/prove the dependencies were right).
> A few problems:
> It seems there are users of TargetSelect.h that want pretty much every
> granular split of the functionality possible. For example:
> * Some executables only depend on the asm parsers and only call
> InitializeAllAsmParsers (similarly for any other All*) - see the various
> AllTargetsAsmParsers and similar rules in cmake/modules/LLVM-Config.cmake
> * Some executables depend only on the native target support
> InitializeNativeTarget* functions - see the JIT tests and the "native" and
> "nativecodegen" rules in the above cmake file.
> So... - any ideas? Should we just give up some of this fine grained
> dependency control & say you can only depend on all targets? (or maybe "all
> targets or the native target" and I'll make two libraries -
> libLLVMAllTargets and libLLVMNativeTarget?)
> Do we keep the fine grained dependency & have
> libLLVM{AllTargets,NativeTarget}{AsmPrinters,AsmParsers,Descs,Disassemblers,Infos}
> ?
> Happy to make any of that happen, but curious what people might prefer.
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