[PowerPC] Replace foul hackery with real calls to __tls_get_addr

My original support for the general dynamic and local dynamic TLS
models contained some fairly obtuse hacks to generate calls to
__tls_get_addr when lowering a TargetGlobalAddress.  Rather than
generating real calls, special GET_TLS_ADDR nodes were used to wrap
the calls and only reveal them at assembly time.  I attempted to
provide correct parameter and return values by chaining CopyToReg and
CopyFromReg nodes onto the GET_TLS_ADDR nodes, but this was also not
fully correct.  Problems were seen with two back-to-back stores to TLS
variables, where the call sequences ended up overlapping with unhappy
results.  Additionally, since these weren't real calls, the proper
register side effects of a call were not recorded, so clobbered values
were kept live across the calls.

The proper thing to do is to lower these into calls in the first
place.  This is relatively straightforward; see the changes to
PPCTargetLowering::LowerGlobalTLSAddress() in PPCISelLowering.cpp.
The changes here are standard call lowering, except that we need to
track the fact that these calls will require a relocation.  This is
done by adding a machine operand flag of MO_TLSLD or MO_TLSGD to the
TargetGlobalAddress operand that appears earlier in the sequence.

The calls to LowerCallTo() eventually find their way to
LowerCall_64SVR4() or LowerCall_32SVR4(), which call FinishCall(),
which calls PrepareCall().  In PrepareCall(), we detect the calls to
__tls_get_addr and immediately snag the TargetGlobalTLSAddress with
the annotated relocation information.  This becomes an extra operand
on the call following the callee, which is expected for nodes of type
tlscall.  We change the call opcode to CALL_TLS for this case.  Back
in FinishCall(), we change it again to CALL_NOP_TLS for 64-bit only,
since we require a TOC-restore nop following the call for the 64-bit
ABIs.

During selection, patterns in PPCInstrInfo.td and PPCInstr64Bit.td
convert the CALL_TLS nodes into BL_TLS nodes, and convert the
CALL_NOP_TLS nodes into BL8_NOP_TLS nodes.  This replaces the code
removed from PPCAsmPrinter.cpp, as the BL_TLS or BL8_NOP_TLS
nodes can now be emitted normally using their patterns and the
associated printTLSCall print method.

Finally, as a result of these changes, all references to get-tls-addr
in its various guises are no longer used, so they have been removed.

There are existing TLS tests to verify the changes haven't messed
anything up).  I've added one new test that verifies that the problem
with the original code has been fixed.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221703 91177308-0d34-0410-b5e6-96231b3b80d8