[Orc] Specialize SerializationTraits on (un)signed char to fix SunOS

[mgorny]

Summary

Specialize the SerializationTraits on 'char', 'signed char'
and 'unsigned char' directly, rather than combining the first one with
'int8_t' and 'uint8_t'. While the latter types are commonly implemented
using 'signed char' and 'unsigned char', there is no guarantee that
a plain 'char' would not be used for their implementation.

This is exactly what happens on SunOS (OpenIndiana), where 'int8_t' is
implemented using 'char' (which is signed by default on the platform).
As a result, the specialization for 'int8_t' is equivalent to the one
for 'char' and causes the build to fail:

In file included from .../lib/ExecutionEngine/Orc/OrcRemoteTargetRPCAPI.cpp:10:
In file included from .../include/llvm/ExecutionEngine/Orc/OrcRemoteTargetRPCAPI.h:19:
.../include/llvm/ExecutionEngine/Orc/RPCByteChannel.h:161:7: error: redefinition of 'SerializationTraits<type-parameter-0-0, char, void>'
class SerializationTraits<ChannelT, char>
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.../psllvm/include/llvm/ExecutionEngine/Orc/RPCByteChannel.h:154:7: note: previous definition is here
class SerializationTraits<ChannelT, int8_t>
      ^
1 error generated.

Therefore, use 'signed char' and 'unsigned char' directly, since both
those types are guaranteed to be distinct from 'char'. They should also
be of the same size as int8_t/uint8_t on all platforms LLVM is being
built on.

[lhames]

Hi Michał,

That's interesting. I think I ran into almost the opposite problem while working on an update to this code: leaving out a specialization for char caused a 'missing specialization' error.

Let me look into this: I suspect we'll actually want to use SFINAE tricks to enable/disable one of the specializations.

Cheers,
Lang.

[mgorny]

In D25501#573356, @lhames wrote:

Hi Michał,

That's interesting. I think I ran into almost the opposite problem while working on an update to this code: leaving out a specialization for char caused a 'missing specialization' error.

Let me look into this: I suspect we'll actually want to use SFINAE tricks to enable/disable one of the specializations.

That was my first thought as well. However, my C++ skills were not enough to be able to get a working SFINAE for this problem. So I went for the simplest alternative, that is specializing all three possible char variants.

[mgorny]

This seems no longer necessary after rL286620. Thanks!

include/llvm/ExecutionEngine/Orc/RPCByteChannel.h

 template <typename ChannelT>
 class SerializationTraits<ChannelT, int16_t>
   : public RPCByteChannelPrimitiveSerialization<ChannelT, int16_t> {
 public:
   static const char* getName() { return "int16_t"; }
 };
 
 template <typename ChannelT>
-class SerializationTraits<ChannelT, uint8_t>
+class SerializationTraits<ChannelT, unsigned char>
   : public RPCByteChannelPrimitiveSerialization<ChannelT, uint8_t> {
 public:
   static const char* getName() { return "uint8_t"; }
 };
 
 template <typename ChannelT>
-class SerializationTraits<ChannelT, int8_t>
+class SerializationTraits<ChannelT, signed char>
   : public RPCByteChannelPrimitiveSerialization<ChannelT, int8_t> {
 public:
   static const char* getName() { return "int8_t"; }
 };
 
 template <typename ChannelT>
 class SerializationTraits<ChannelT, char>
   : public RPCByteChannelPrimitiveSerialization<ChannelT, uint8_t> {