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.

llvm-svn: 179156

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
index 51bc4f23cce..773b62326fb 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/llvm/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;
   }
 }