[PowerPC] Support @h modifier

This adds necessary infrastructure to support the @h modifier.
Note that all required relocation types were already present
(and unused).

This patch provides support for using @h in the assembler;
it would also be possible to now use this feature in code
generated by the compiler, but this is not done yet.

llvm-svn: 184548
diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCExpr.cpp b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCExpr.cpp
index b29d6ff..8a346b4 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCExpr.cpp
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCExpr.cpp
@@ -27,6 +27,7 @@
     switch (Kind) {
     default: llvm_unreachable("Invalid kind!");
     case VK_PPC_LO: OS << "lo16"; break;
+    case VK_PPC_HI: OS << "hi16"; break;
     case VK_PPC_HA: OS << "ha16"; break;
     }
 
@@ -39,6 +40,7 @@
     switch (Kind) {
     default: llvm_unreachable("Invalid kind!");
     case VK_PPC_LO: OS << "@l"; break;
+    case VK_PPC_HI: OS << "@h"; break;
     case VK_PPC_HA: OS << "@ha"; break;
     }
   }
@@ -60,6 +62,9 @@
       case VK_PPC_LO:
         Result = Result & 0xffff;
         break;
+      case VK_PPC_HI:
+        Result = (Result >> 16) & 0xffff;
+        break;
       case VK_PPC_HA:
         Result = ((Result >> 16) + ((Result & 0x8000) ? 1 : 0)) & 0xffff;
         break;
@@ -77,6 +82,9 @@
       case VK_PPC_LO:
         Modifier = MCSymbolRefExpr::VK_PPC_LO;
         break;
+      case VK_PPC_HI:
+        Modifier = MCSymbolRefExpr::VK_PPC_HI;
+        break;
       case VK_PPC_HA:
         Modifier = MCSymbolRefExpr::VK_PPC_HA;
         break;