[AIX] Implement function descriptor on SDAG

Summary:
(1) Function descriptor on AIX
On AIX, a called routine may have 2 distinct symbols associated with it:
 * A function descriptor (Name)
 * A function entry point (.Name)

The descriptor structure on AIX is the same as those in the ELF V1 ABI:
 * The address of the entry point of the function.
 * The TOC base address for the function.
 * The environment pointer.

The descriptor symbol uses the same name as the source level function in C.
The function entry point is analogous to the symbol we would generate for a
 function in a non-descriptor-based ABI, except that it is renamed by
prepending a ".".

Which symbol gets referenced depends on the context:
 * Taking the address of the function references the descriptor symbol.
 * Calling the function references the entry point symbol.

(2) Speaking of implementation on AIX, for direct function call target, we
 create proper MCSymbol SDNode(e.g . ".foo") while constructing SDAG to
 replace original TargetGlobalAddress SDNode. Then down the path, we can
 take advantage of this MCSymbol.

Patch by: Xiangling_L

Reviewed by: sfertile, hubert.reinterpretcast, jasonliu, syzaara

Differential Revision: https://reviews.llvm.org/D62532

llvm-svn: 362735

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/MC/MCContext.cpp b/llvm/lib/MC/MCContext.cpp
index e83702eebe0..43a7e8a64af 100644
--- a/llvm/lib/MC/MCContext.cpp
+++ b/llvm/lib/MC/MCContext.cpp
@@ -32,6 +32,7 @@
 #include "llvm/MC/MCSymbolELF.h"
 #include "llvm/MC/MCSymbolMachO.h"
 #include "llvm/MC/MCSymbolWasm.h"
+#include "llvm/MC/MCSymbolXCOFF.h"
 #include "llvm/MC/SectionKind.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
@@ -162,8 +163,7 @@ MCSymbol *MCContext::createSymbolImpl(const StringMapEntry<bool> *Name,
     case MCObjectFileInfo::IsWasm:
       return new (Name, *this) MCSymbolWasm(Name, IsTemporary);
     case MCObjectFileInfo::IsXCOFF:
-      // TODO: Need to implement class MCSymbolXCOFF.
-      break;
+      return new (Name, *this) MCSymbolXCOFF(Name, IsTemporary);
     }
   }
   return new (Name, *this) MCSymbol(MCSymbol::SymbolKindUnset, Name,