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

5 files changed, 208 insertions, 0 deletions

diff --git a/lib/Target/PowerPC/PPCInstr64Bit.td b/lib/Target/PowerPC/PPCInstr64Bit.td
index 5848291..a3049d4a 100644
--- a/lib/Target/PowerPC/PPCInstr64Bit.td
+++ b/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 {
diff --git a/lib/Target/PowerPC/PPCInstrInfo.cpp b/lib/Target/PowerPC/PPCInstrInfo.cpp
index 219d893..51bc4f2 100644
--- a/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -876,6 +876,143 @@ bool PPCInstrInfo::FoldImmediate(MachineInstr *UseMI, MachineInstr *DefMI,
   return true;
 }
 
+bool PPCInstrInfo::isPredicated(const MachineInstr *MI) const {
+  unsigned OpC = MI->getOpcode();
+  switch (OpC) {
+  default:
+    return false;
+  case PPC::BCC:
+  case PPC::BCLR:
+  case PPC::BDZLR:
+  case PPC::BDZLR8:
+  case PPC::BDNZLR:
+  case PPC::BDNZLR8:
+    return true;
+  }
+}
+
+bool PPCInstrInfo::isUnpredicatedTerminator(const MachineInstr *MI) const {
+  if (!MI->isTerminator())
+    return false;
+
+  // Conditional branch is a special case.
+  if (MI->isBranch() && !MI->isBarrier())
+    return true;
+
+  return !isPredicated(MI);
+}
+
+bool PPCInstrInfo::PredicateInstruction(
+                     MachineInstr *MI,
+                     const SmallVectorImpl<MachineOperand> &Pred) const {
+  unsigned OpC = MI->getOpcode();
+  if (OpC == PPC::BLR) {
+    if (Pred[1].getReg() == PPC::CTR8 || Pred[1].getReg() == PPC::CTR) {
+      bool isPPC64 = TM.getSubtargetImpl()->isPPC64();
+      MI->setDesc(get(Pred[0].getImm() ?
+                      (isPPC64 ? PPC::BDNZLR8 : PPC::BDNZLR) :
+                      (isPPC64 ? PPC::BDZLR8  : PPC::BDZLR)));
+    } else {
+      MI->setDesc(get(PPC::BCLR));
+      MachineInstrBuilder(*MI->getParent()->getParent(), MI)
+        .addImm(Pred[0].getImm())
+        .addReg(Pred[1].getReg());
+    }
+
+    return true;
+  } else if (OpC == PPC::B) {
+    if (Pred[1].getReg() == PPC::CTR8 || Pred[1].getReg() == PPC::CTR) {
+      bool isPPC64 = TM.getSubtargetImpl()->isPPC64();
+      MI->setDesc(get(Pred[0].getImm() ?
+                      (isPPC64 ? PPC::BDNZ8 : PPC::BDNZ) :
+                      (isPPC64 ? PPC::BDZ8  : PPC::BDZ)));
+    } else {
+      MachineBasicBlock *MBB = MI->getOperand(0).getMBB();
+      MI->RemoveOperand(0);
+
+      MI->setDesc(get(PPC::BCC));
+      MachineInstrBuilder(*MI->getParent()->getParent(), MI)
+        .addImm(Pred[0].getImm())
+        .addReg(Pred[1].getReg())
+        .addMBB(MBB);
+    }
+
+    return true;
+  }
+
+  return false;
+}
+
+bool PPCInstrInfo::SubsumesPredicate(
+                     const SmallVectorImpl<MachineOperand> &Pred1,
+                     const SmallVectorImpl<MachineOperand> &Pred2) const {
+  assert(Pred1.size() == 2 && "Invalid PPC first predicate");
+  assert(Pred2.size() == 2 && "Invalid PPC second predicate");
+
+  if (Pred1[1].getReg() == PPC::CTR8 || Pred1[1].getReg() == PPC::CTR)
+    return false;
+  if (Pred2[1].getReg() == PPC::CTR8 || Pred2[1].getReg() == PPC::CTR)
+    return false;
+
+  PPC::Predicate P1 = (PPC::Predicate) Pred1[0].getImm();
+  PPC::Predicate P2 = (PPC::Predicate) Pred2[0].getImm();
+
+  if (P1 == P2)
+    return true;
+
+  // Does P1 subsume P2, e.g. GE subsumes GT.
+  if (P1 == PPC::PRED_LE &&
+      (P2 == PPC::PRED_LT || P2 == PPC::PRED_EQ))
+    return true;
+  if (P1 == PPC::PRED_GE &&
+      (P2 == PPC::PRED_GT || P2 == PPC::PRED_EQ))
+    return true;
+
+  return false;
+}
+
+bool PPCInstrInfo::DefinesPredicate(MachineInstr *MI,
+                                    std::vector<MachineOperand> &Pred) const {
+  // Note: At the present time, the contents of Pred from this function is
+  // unused by IfConversion. This implementation follows ARM by pushing the
+  // CR-defining operand. Because the 'DZ' and 'DNZ' count as types of
+  // predicate, instructions defining CTR or CTR8 are also included as
+  // predicate-defining instructions.
+
+  const TargetRegisterClass *RCs[] =
+    { &PPC::CRRCRegClass, &PPC::CRBITRCRegClass,
+      &PPC::CTRRCRegClass, &PPC::CTRRC8RegClass };
+
+  bool Found = false;
+  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    for (int c = 0; c < 2 && !Found; ++c) {
+      const TargetRegisterClass *RC = RCs[c];
+      for (TargetRegisterClass::iterator I = RC->begin(),
+           IE = RC->end(); I != IE; ++I) {
+        if ((MO.isRegMask() && MO.clobbersPhysReg(*I)) ||
+            (MO.isReg() && MO.isDef() && MO.getReg() == *I)) {
+          Pred.push_back(MO);
+          Found = true;
+        }
+      }
+    }
+  }
+
+  return Found;
+}
+
+bool PPCInstrInfo::isPredicable(MachineInstr *MI) const {
+  unsigned OpC = MI->getOpcode();
+  switch (OpC) {
+  default:
+    return false;
+  case PPC::B:
+  case PPC::BLR:
+    return true;
+  }
+}
+
 /// GetInstSize - Return the number of bytes of code the specified
 /// instruction may be.  This returns the maximum number of bytes.
 ///
diff --git a/lib/Target/PowerPC/PPCInstrInfo.h b/lib/Target/PowerPC/PPCInstrInfo.h
index fe3b84c..a6ab617 100644
--- a/lib/Target/PowerPC/PPCInstrInfo.h
+++ b/lib/Target/PowerPC/PPCInstrInfo.h
@@ -160,6 +160,53 @@ public:
   virtual bool FoldImmediate(MachineInstr *UseMI, MachineInstr *DefMI,
                              unsigned Reg, MachineRegisterInfo *MRI) const;
 
+  // If conversion by predication (only supported by some branch instructions).
+  // All of the profitability checks always return true; it is always
+  // profitable to use the predicated branches.
+  virtual bool isProfitableToIfCvt(MachineBasicBlock &MBB,
+                                   unsigned NumCycles, unsigned ExtraPredCycles,
+                                   const BranchProbability &Probability) const {
+    return true;
+  }
+
+  virtual bool isProfitableToIfCvt(MachineBasicBlock &TMBB,
+                                   unsigned NumT, unsigned ExtraT,
+                                   MachineBasicBlock &FMBB,
+                                   unsigned NumF, unsigned ExtraF,
+                                   const BranchProbability &Probability) const {
+    return true;
+  }
+
+  virtual bool isProfitableToDupForIfCvt(MachineBasicBlock &MBB,
+                                         unsigned NumCycles,
+                                         const BranchProbability
+                                         &Probability) const {
+    return true;
+  }
+
+  virtual bool isProfitableToUnpredicate(MachineBasicBlock &TMBB,
+                                         MachineBasicBlock &FMBB) const {
+    return false;
+  }
+
+  // Predication support.
+  bool isPredicated(const MachineInstr *MI) const;
+
+  virtual bool isUnpredicatedTerminator(const MachineInstr *MI) const;
+
+  virtual
+  bool PredicateInstruction(MachineInstr *MI,
+                            const SmallVectorImpl<MachineOperand> &Pred) const;
+
+  virtual
+  bool SubsumesPredicate(const SmallVectorImpl<MachineOperand> &Pred1,
+                         const SmallVectorImpl<MachineOperand> &Pred2) const;
+
+  virtual bool DefinesPredicate(MachineInstr *MI,
+                                std::vector<MachineOperand> &Pred) const;
+
+  virtual bool isPredicable(MachineInstr *MI) const;
+
   /// GetInstSize - Return the number of bytes of code the specified
   /// instruction may be.  This returns the maximum number of bytes.
   ///
diff --git a/lib/Target/PowerPC/PPCInstrInfo.td b/lib/Target/PowerPC/PPCInstrInfo.td
index 37b1a0b..11969fe 100644
--- a/lib/Target/PowerPC/PPCInstrInfo.td
+++ b/lib/Target/PowerPC/PPCInstrInfo.td
@@ -518,6 +518,13 @@ let isBranch = 1, isTerminator = 1, hasCtrlDep = 1, PPC970_Unit = 7 in {
     let isReturn = 1, Uses = [LR, RM] in
     def BCLR : XLForm_2_br<19, 16, 0, (outs), (ins pred:$cond),
                            "b${cond:cc}lr ${cond:reg}", BrB, []>;
+
+    let isReturn = 1, Defs = [CTR], Uses = [CTR, LR, RM] in {
+      def BDZLR  : XLForm_2_ext<19, 16, 18, 0, 0, (outs), (ins),
+                             "bdzlr", BrB, []>;
+      def BDNZLR : XLForm_2_ext<19, 16, 16, 0, 0, (outs), (ins),
+                             "bdnzlr", BrB, []>;
+    }
   }
 
   let Defs = [CTR], Uses = [CTR] in {
diff --git a/lib/Target/PowerPC/PPCTargetMachine.cpp b/lib/Target/PowerPC/PPCTargetMachine.cpp
index caf5c98..14dc794 100644
--- a/lib/Target/PowerPC/PPCTargetMachine.cpp
+++ b/lib/Target/PowerPC/PPCTargetMachine.cpp
@@ -93,6 +93,7 @@ public:
   virtual bool addPreRegAlloc();
   virtual bool addILPOpts();
   virtual bool addInstSelector();
+  virtual bool addPreSched2();
   virtual bool addPreEmitPass();
 };
 } // namespace
@@ -123,6 +124,13 @@ bool PPCPassConfig::addInstSelector() {
   return false;
 }
 
+bool PPCPassConfig::addPreSched2() {
+  if (getOptLevel() != CodeGenOpt::None)
+    addPass(&IfConverterID);
+
+  return true;
+}
+
 bool PPCPassConfig::addPreEmitPass() {
   if (getOptLevel() != CodeGenOpt::None)
     addPass(createPPCEarlyReturnPass());