PPC: Prep for if conversion of bctr[l]

This adds in-principle support for if-converting the bctr[l] instructions.
These instructions are used for indirect branching. It seems, however, that the
current if converter will never actually predicate these. To do so, it would
need the ability to hoist a few setup insts. out of the conditionally-executed
block. For example, code like this:
  void foo(int a, int (*bar)()) { if (a != 0) bar(); }
becomes:
        ...
        beq 0, .LBB0_2
        std 2, 40(1)
        mr 12, 4
        ld 3, 0(4)
        ld 11, 16(4)
        ld 2, 8(4)
        mtctr 3
        bctrl
        ld 2, 40(1)
.LBB0_2:
        ...
and it would be safe to do all of this unconditionally with a predicated
beqctrl instruction.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179156 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/PowerPC/PPCInstr64Bit.td

@@ -67,9 +67,14 @@ def HI48_64 : SDNodeXForm<imm, [{
 //
 
 let isTerminator = 1, isBarrier = 1, PPC970_Unit = 7 in {
-  let isBranch = 1, isIndirectBranch = 1, Uses = [CTR8] in
+  let isBranch = 1, isIndirectBranch = 1, Uses = [CTR8] in {
     def BCTR8 : XLForm_2_ext<19, 528, 20, 0, 0, (outs), (ins), "bctr", BrB, []>,
         Requires<[In64BitMode]>;
+
+    def BCCTR8 : XLForm_2_br<19, 528, 0, (outs), (ins pred:$cond),
+                             "b${cond:cc}ctr ${cond:reg}", BrB, []>,
+        Requires<[In64BitMode]>;
+  }
 }
 
 let Defs = [LR8] in
@@ -125,6 +130,9 @@ let isCall = 1, PPC970_Unit = 7, Defs = [LR8] in {
     def BCTRL8 : XLForm_2_ext<19, 528, 20, 0, 1, (outs), (ins),
                               "bctrl", BrB, [(PPCbctrl)]>,
                  Requires<[In64BitMode]>;
+    def BCCTRL8 : XLForm_2_br<19, 528, 1, (outs), (ins pred:$cond),
+                              "b${cond:cc}ctrl ${cond:reg}", BrB, []>,
+        Requires<[In64BitMode]>;
   }
 }
 

lib/Target/PowerPC/PPCInstrInfo.cpp

@@ -882,6 +882,10 @@ bool PPCInstrInfo::isPredicated(const MachineInstr *MI) const {
   default:
     return false;
   case PPC::BCC:
+  case PPC::BCCTR:
+  case PPC::BCCTR8:
+  case PPC::BCCTRL:
+  case PPC::BCCTRL8:
   case PPC::BCLR:
   case PPC::BDZLR:
   case PPC::BDZLR8:
@@ -938,6 +942,19 @@ bool PPCInstrInfo::PredicateInstruction(
     }
 
     return true;
+  } else if (OpC == PPC::BCTR  || OpC == PPC::BCTR8 ||
+             OpC == PPC::BCTRL || OpC == PPC::BCTRL8) {
+    if (Pred[1].getReg() == PPC::CTR8 || Pred[1].getReg() == PPC::CTR)
+      llvm_unreachable("Cannot predicate bctr[l] on the ctr register");
+
+    bool setLR = OpC == PPC::BCTRL || OpC == PPC::BCTRL8;
+    bool isPPC64 = TM.getSubtargetImpl()->isPPC64();
+    MI->setDesc(get(isPPC64 ? (setLR ? PPC::BCCTRL8 : PPC::BCCTR8) :
+                              (setLR ? PPC::BCCTRL  : PPC::BCCTR)));
+    MachineInstrBuilder(*MI->getParent()->getParent(), MI)
+      .addImm(Pred[0].getImm())
+      .addReg(Pred[1].getReg());
+    return true;
   }
 
   return false;
@@ -1009,6 +1026,10 @@ bool PPCInstrInfo::isPredicable(MachineInstr *MI) const {
     return false;
   case PPC::B:
   case PPC::BLR:
+  case PPC::BCTR:
+  case PPC::BCTR8:
+  case PPC::BCTRL:
+  case PPC::BCTRL8:
     return true;
   }
 }

lib/Target/PowerPC/PPCInstrInfo.td

@@ -493,8 +493,12 @@ let isTerminator = 1, isBarrier = 1, PPC970_Unit = 7 in {
   let isReturn = 1, Uses = [LR, RM] in
     def BLR : XLForm_2_ext<19, 16, 20, 0, 0, (outs), (ins), "blr", BrB,
                            [(retflag)]>;
-  let isBranch = 1, isIndirectBranch = 1, Uses = [CTR] in
+  let isBranch = 1, isIndirectBranch = 1, Uses = [CTR] in {
     def BCTR : XLForm_2_ext<19, 528, 20, 0, 0, (outs), (ins), "bctr", BrB, []>;
+
+    def BCCTR : XLForm_2_br<19, 528, 0, (outs), (ins pred:$cond),
+                            "b${cond:cc}ctr ${cond:reg}", BrB, []>;
+  }
 }
 
 let Defs = [LR] in
@@ -555,6 +559,8 @@ let isCall = 1, PPC970_Unit = 7, Defs = [LR] in {
     def BCTRL : XLForm_2_ext<19, 528, 20, 0, 1, (outs), (ins),
                              "bctrl", BrB, [(PPCbctrl)]>,
                 Requires<[In32BitMode]>;
+    def BCCTRL : XLForm_2_br<19, 528, 1, (outs), (ins pred:$cond),
+                             "b${cond:cc}ctrl ${cond:reg}", BrB, []>;
   }
 }