llvm dev - Sep 2017 - Codegen from memory fails, works from .bc and .ll (X86 + NVPTX)

Hi

I’m working on getting LDC (the LVM D Compiler) to produce both host code and
PTX with one pass though our front end.
Compiling for host works. Compiling for PTX works .We error out on the use of
global variables in code destined for PTX.

I've hit what appears to be an impossible bug: 

I can generate both .bc and .ll’s that can be passed to llc to generate .ptx but
if I try to output it straight from the in memory representation I get

LLVM ERROR: Cannot select: 0x7f8854268fa0: i64 = GlobalTLSAddress<i32
addrspace(1)* @_variable> 0
In function: _function
(This error originates from SelectionDAGISel)

if I have a thread local global in my host code. If I change that to a c style
global I get a segfault instead.

Both the host code and PTX code share a context, but are codegen'd into
different LLVM modules.
Both ‘variable’ (defined in addrspace 0) and ‘function' are defined and used
exclusively in the code for the host.
Code generation (IR construction and writing files out to disk) for the host is
done before any codegen for PTX.

In the case of the thread local global it still appears to produce and
successfully write to disk a valid .ptx
(and obviously doesn’t for the segfaulting case).

Tested with LDC master LLVM trunk (a few days old) on both windows and OS X.

A few questions, before I submit a bug report:

Is this an LLVM fault, or a producer fault?
If it is an LLVM fault, do you have any tips on how to get a test case (beyond
LDC and the project that triggers it)?
A .bc is already just a dump of the in-memory representation isn’t it?

The LDC bug report: https://github.com/ldc-developers/ldc/issues/2307

Thanks
Nic