[PowerPC] Make LDtocL and friends invariant loads

LDtocL, and other loads that roughly correspond to the TOC_ENTRY SDAG node,
represent loads from the TOC, which is invariant. As a result, these loads can
be hoisted out of loops, etc. In order to do this, we need to generate
GOT-style MMOs for TOC_ENTRY, which requires treating it as a legitimate memory
intrinsic node type. Once this is done, the MMO transfer is automatically
handled for TableGen-driven instruction selection, and for nodes generated
directly in PPCISelDAGToDAG, we need to transfer the MMOs manually.

Also, we were not transferring MMOs associated with pre-increment loads, so do
that too.

Lastly, this fixes an exposed bug where R30 was not added as a defined operand of
UpdateGBR.

This problem was highlighted by an example (used to generate the test case)
posted to llvmdev by Francois Pichet.

llvm-svn: 230553
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index a2a8241..faa1e3f 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -71,8 +71,6 @@
       /// though these are usually folded into other nodes.
       Hi, Lo,
 
-      TOC_ENTRY,
-
       /// The following two target-specific nodes are used for calls through
       /// function pointers in the 64-bit SVR4 ABI.
 
@@ -337,7 +335,12 @@
 
       /// QBRC, CHAIN = QVLFSb CHAIN, Ptr
       /// The 4xf32 load used for v4i1 constants.
-      QVLFSb
+      QVLFSb,
+
+      /// GPRC = TOC_ENTRY GA, TOC
+      /// Loads the entry for GA from the TOC, where the TOC base is given by
+      /// the last operand.
+      TOC_ENTRY
     };
   }