Fix dynamic linking on PPC64.

Dynamic linking on PPC64 has had problems since we had to move the top-down
hazard-detection logic post-ra. For dynamic linking to work there needs to be
a nop placed after every call. It turns out that it is really hard to guarantee
that nothing will be placed in between the call (bl) and the nop during post-ra
scheduling. Previous attempts at fixing this by placing logic inside the
hazard detector only partially worked.

This is now fixed in a different way: call+nop codegen-only instructions. As far
as CodeGen is concerned the pair is now a single instruction and cannot be split.
This solution works much better than previous attempts.

The scoreboard hazard detector is also renamed to be more generic, there is currently
no cpu-specific logic in it.

llvm-svn: 153816
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index 2e046c4..e79229f 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -95,7 +95,9 @@
       EXTSW_32,
 
       /// CALL - A direct function call.
-      CALL_Darwin, CALL_SVR4,
+      /// CALL_NOP_SVR4 is a call with the special  NOP which follows 64-bit
+      /// SVR4 calls.
+      CALL_Darwin, CALL_SVR4, CALL_NOP_SVR4,
 
       /// NOP - Special NOP which follows 64-bit SVR4 calls.
       NOP,