Allow PPC B and BLR to be if-converted into some predicated forms

This enables us to form predicated branches (which are the same conditional
branches we had before) and also a larger set of predicated returns (including
instructions like bdnzlr which is a conditional return and loop-counter
decrement all in one).

At the moment, if conversion does not capture all possible opportunities. A
simple example is provided in early-ret2.ll, where if conversion forms one
predicated return, and then the PPCEarlyReturn pass picks up the other one. So,
at least for now, we'll keep both mechanisms.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179134 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/PowerPC/PPCInstr64Bit.td

@@ -83,8 +83,17 @@ let isBranch = 1, isTerminator = 1, hasCtrlDep = 1, PPC970_Unit = 7 in {
     def BDNZ8 : BForm_1<16, 16, 0, 0, (outs), (ins condbrtarget:$dst),
                         "bdnz $dst">;
   }
+
+  let isReturn = 1, Defs = [CTR8], Uses = [CTR8, LR8, RM] in {
+    def BDZLR8  : XLForm_2_ext<19, 16, 18, 0, 0, (outs), (ins),
+                              "bdzlr", BrB, []>;
+    def BDNZLR8 : XLForm_2_ext<19, 16, 16, 0, 0, (outs), (ins),
+                              "bdnzlr", BrB, []>;
+  }
 }
 
+
+
 let isCall = 1, PPC970_Unit = 7, Defs = [LR8] in {
   // Convenient aliases for call instructions
   let Uses = [RM] in {