[llvm-dev] What's LLVM{target}CodeGen vs {target}CodeGen?

[Robert Baruch via llvm-dev]

Hi all,

*TL;DR:* I have a target TMS9900CodeGen but cmake is looking for LLVMTMS9900
or LLVMTMS9900CodeGen which I don't have, and cmake dies. But the MSP430 target
doesn't have that either, and cmake is happy with it. What am I missing?

*The premise:*

I may be making a huge mistake, but I'm trying to develop an LLVM backend.
I'm writing up some notes while I do so, and I hope to update the
documentation. However, I ran into a bit of a problem running cmake. Note
that I built the trunk release just fine, right now I'm modifying it.

*The setup:*

My target is called TMS9900 because I'm a masochist, and I'm just trying to
make a bare do-nothing skeleton to start with. I have this:

lib/Target/TMS9900
  - CMakeLists.txt
  - LLVMBuild.txt
  - TMS9900TargetMachine.cpp
  - TMS9900TargetMachine.h
  - TMS9900.td

TMS9900TargetMachine is the barest class I could make. It derives from
LLVMTargetMachine, and passes everything through (although it defines the
DataLayout).

CMakeLists.txt is also pretty small:

set(LLVM_TARGET_DEFINITIONS TMS9900.td)

add_llvm_library(TMS9900CodeGen
  TMS9900TargetMachine.cpp
  )

LLVMBuild.txt is as minimal as I could guess at:

[common]
subdirectories =

[component_0]
type = TargetGroup
name = TMS9900
parent = Target

[component_1]
type = Library
name = TMS9900CodeGen
parent = TMS9900
required_libraries = Analysis AsmPrinter CodeGen Core MC Scalar
SelectionDAG Support Target TransformUtils
add_to_library_groups = TMS9900

And finally, TMS9900.td contains:

include "llvm/Target/Target.td"
def TMS9900 : Target { }

I also updated lib/Target/LLVMBuild.txt's [common] subdirectories to
include TMS9900.

*The punchline:*

Now, I tried to run cmake:

$ cd build
$ cmake -G "Unix Makefiles" -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=TMS9900
../llvm
... stuff ...
CMake Error at cmake/modules/LLVM-Config.cmake:178 (message):
  Target TMS9900 is not in the set of libraries.
Call Stack (most recent call first):
  cmake/modules/AddLLVM.cmake:525 (llvm_map_components_to_libnames)
  cmake/modules/AddLLVM.cmake:574 (llvm_add_library)
  tools/lto/CMakeLists.txt:19 (add_llvm_library)

(Line numbers may be off slightly, since I added some message() lines). So
I tracked this error down to where LLVM-Config.cmake is looking for targets
whose name, given {target}, is either LLVM{target} or LLVM{target}CodeGen.

Of course, I have no such targets.

The weird thing is that I looked at the MSP430 directory, and it does not
have LLVMMSP430 or LLVMMSP430CodeGen, either. It just has MSP430CodeGen yet
somehow that target works just fine.

*What am I missing?*

Thanks!

--Rob
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