Enable early if conversion on PPC

On cores for which we know the misprediction penalty, and we have
the isel instruction, we can profitably perform early if conversion.
This enables us to replace some small branch sequences with selects
and avoid the potential stalls from mispredicting the branches.

Enabling this feature required implementing canInsertSelect and
insertSelect in PPCInstrInfo; isel code in PPCISelLowering was
refactored to use these functions as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178926 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/PowerPC/PPCISelLowering.cpp

@@ -71,6 +71,7 @@ PPCTargetLowering::PPCTargetLowering(PPCTargetMachine &TM)
   : TargetLowering(TM, CreateTLOF(TM)), PPCSubTarget(*TM.getSubtargetImpl()) {
   const PPCSubtarget *Subtarget = &TM.getSubtarget<PPCSubtarget>();
   PPCRegInfo = TM.getRegisterInfo();
+  PPCII = TM.getInstrInfo();
 
   setPow2DivIsCheap();
 
@@ -6239,29 +6240,13 @@ PPCTargetLowering::EmitInstrWithCustomInserter(MachineInstr *MI,
 
   if (PPCSubTarget.hasISEL() && (MI->getOpcode() == PPC::SELECT_CC_I4 ||
                                  MI->getOpcode() == PPC::SELECT_CC_I8)) {
-    unsigned OpCode = MI->getOpcode() == PPC::SELECT_CC_I8 ?
+    SmallVector<MachineOperand, 2> Cond;
-                                         PPC::ISEL8 : PPC::ISEL;
+    Cond.push_back(MI->getOperand(4));
-    unsigned SelectPred = MI->getOperand(4).getImm();
+    Cond.push_back(MI->getOperand(1));
+
     DebugLoc dl = MI->getDebugLoc();
-
+    PPCII->insertSelect(*BB, MI, dl, MI->getOperand(0).getReg(), Cond,
-    unsigned SubIdx;
+                        MI->getOperand(2).getReg(), MI->getOperand(3).getReg());
-    bool SwapOps;
-    switch (SelectPred) {
-    default: llvm_unreachable("invalid predicate for isel");
-    case PPC::PRED_EQ: SubIdx = PPC::sub_eq; SwapOps = false; break;
-    case PPC::PRED_NE: SubIdx = PPC::sub_eq; SwapOps = true; break;
-    case PPC::PRED_LT: SubIdx = PPC::sub_lt; SwapOps = false; break;
-    case PPC::PRED_GE: SubIdx = PPC::sub_lt; SwapOps = true; break;
-    case PPC::PRED_GT: SubIdx = PPC::sub_gt; SwapOps = false; break;
-    case PPC::PRED_LE: SubIdx = PPC::sub_gt; SwapOps = true; break;
-    case PPC::PRED_UN: SubIdx = PPC::sub_un; SwapOps = false; break;
-    case PPC::PRED_NU: SubIdx = PPC::sub_un; SwapOps = true; break;
-    }
-
-    BuildMI(*BB, MI, dl, TII->get(OpCode), MI->getOperand(0).getReg())
-      .addReg(MI->getOperand(SwapOps? 3 : 2).getReg())
-      .addReg(MI->getOperand(SwapOps? 2 : 3).getReg())
-      .addReg(MI->getOperand(1).getReg(), 0, SubIdx);
   } else if (MI->getOpcode() == PPC::SELECT_CC_I4 ||
              MI->getOpcode() == PPC::SELECT_CC_I8 ||
              MI->getOpcode() == PPC::SELECT_CC_F4 ||

lib/Target/PowerPC/PPCISelLowering.h

@@ -16,6 +16,7 @@
 #define LLVM_TARGET_POWERPC_PPC32ISELLOWERING_H
 
 #include "PPC.h"
+#include "PPCInstrInfo.h"
 #include "PPCRegisterInfo.h"
 #include "PPCSubtarget.h"
 #include "llvm/CodeGen/SelectionDAG.h"
@@ -327,6 +328,7 @@ namespace llvm {
   class PPCTargetLowering : public TargetLowering {
     const PPCSubtarget &PPCSubTarget;
     const PPCRegisterInfo *PPCRegInfo;
+    const PPCInstrInfo *PPCII;
 
   public:
     explicit PPCTargetLowering(PPCTargetMachine &TM);

lib/Target/PowerPC/PPCInstrInfo.cpp

@@ -417,6 +417,105 @@ PPCInstrInfo::InsertBranch(MachineBasicBlock &MBB, MachineBasicBlock *TBB,
   return 2;
 }
 
+// Select analysis.
+bool PPCInstrInfo::canInsertSelect(const MachineBasicBlock &MBB,
+                const SmallVectorImpl<MachineOperand> &Cond,
+                unsigned TrueReg, unsigned FalseReg,
+                int &CondCycles, int &TrueCycles, int &FalseCycles) const {
+  if (!TM.getSubtargetImpl()->hasISEL())
+    return false;
+
+  if (Cond.size() != 2)
+    return false;
+
+  // If this is really a bdnz-like condition, then it cannot be turned into a
+  // select.
+  if (Cond[1].getReg() == PPC::CTR || Cond[1].getReg() == PPC::CTR8)
+    return false;
+
+  // Check register classes.
+  const MachineRegisterInfo &MRI = MBB.getParent()->getRegInfo();
+  const TargetRegisterClass *RC =
+    RI.getCommonSubClass(MRI.getRegClass(TrueReg), MRI.getRegClass(FalseReg));
+  if (!RC)
+    return false;
+
+  // isel is for regular integer GPRs only.
+  if (!PPC::GPRCRegClass.hasSubClassEq(RC) &&
+      !PPC::G8RCRegClass.hasSubClassEq(RC))
+    return false;
+
+  // FIXME: These numbers are for the A2, how well they work for other cores is
+  // an open question. On the A2, the isel instruction has a 2-cycle latency
+  // but single-cycle throughput. These numbers are used in combination with
+  // the MispredictPenalty setting from the active SchedMachineModel.
+  CondCycles = 1;
+  TrueCycles = 1;
+  FalseCycles = 1;
+
+  return true;
+}
+
+void PPCInstrInfo::insertSelect(MachineBasicBlock &MBB,
+                                MachineBasicBlock::iterator MI, DebugLoc dl,
+                                unsigned DestReg,
+                                const SmallVectorImpl<MachineOperand> &Cond,
+                                unsigned TrueReg, unsigned FalseReg) const {
+  assert(Cond.size() == 2 &&
+         "PPC branch conditions have two components!");
+
+  assert(TM.getSubtargetImpl()->hasISEL() &&
+         "Cannot insert select on target without ISEL support");
+
+  // Get the register classes.
+  MachineRegisterInfo &MRI = MBB.getParent()->getRegInfo();
+  const TargetRegisterClass *RC =
+    RI.getCommonSubClass(MRI.getRegClass(TrueReg), MRI.getRegClass(FalseReg));
+  assert(RC && "TrueReg and FalseReg must have overlapping register classes");
+  assert((PPC::GPRCRegClass.hasSubClassEq(RC) ||
+          PPC::G8RCRegClass.hasSubClassEq(RC)) &&
+         "isel is for regular integer GPRs only");
+
+  unsigned OpCode =
+    PPC::GPRCRegClass.hasSubClassEq(RC) ? PPC::ISEL : PPC::ISEL8;
+  unsigned SelectPred = Cond[0].getImm();
+
+  unsigned SubIdx;
+  bool SwapOps;
+  switch (SelectPred) {
+  default: llvm_unreachable("invalid predicate for isel");
+  case PPC::PRED_EQ: SubIdx = PPC::sub_eq; SwapOps = false; break;
+  case PPC::PRED_NE: SubIdx = PPC::sub_eq; SwapOps = true; break;
+  case PPC::PRED_LT: SubIdx = PPC::sub_lt; SwapOps = false; break;
+  case PPC::PRED_GE: SubIdx = PPC::sub_lt; SwapOps = true; break;
+  case PPC::PRED_GT: SubIdx = PPC::sub_gt; SwapOps = false; break;
+  case PPC::PRED_LE: SubIdx = PPC::sub_gt; SwapOps = true; break;
+  case PPC::PRED_UN: SubIdx = PPC::sub_un; SwapOps = false; break;
+  case PPC::PRED_NU: SubIdx = PPC::sub_un; SwapOps = true; break;
+  }
+
+  unsigned FirstReg =  SwapOps ? FalseReg : TrueReg,
+           SecondReg = SwapOps ? TrueReg  : FalseReg;
+
+  // The first input register of isel cannot be r0. If it is a member
+  // of a register class that can be r0, then copy it first (the
+  // register allocator should eliminate the copy).
+  if (MRI.getRegClass(FirstReg)->contains(PPC::R0) ||
+      MRI.getRegClass(FirstReg)->contains(PPC::X0)) {
+    const TargetRegisterClass *FirstRC =
+      MRI.getRegClass(FirstReg)->contains(PPC::X0) ?
+        &PPC::G8RC_NOX0RegClass : &PPC::GPRC_NOR0RegClass;
+    unsigned OldFirstReg = FirstReg;
+    FirstReg = MRI.createVirtualRegister(FirstRC);
+    BuildMI(MBB, MI, dl, get(TargetOpcode::COPY), FirstReg)
+      .addReg(OldFirstReg);
+  }
+
+  BuildMI(MBB, MI, dl, get(OpCode), DestReg)
+    .addReg(FirstReg).addReg(SecondReg)
+    .addReg(Cond[1].getReg(), 0, SubIdx);
+}
+
 void PPCInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
                                MachineBasicBlock::iterator I, DebugLoc DL,
                                unsigned DestReg, unsigned SrcReg,

lib/Target/PowerPC/PPCInstrInfo.h

@@ -120,6 +120,17 @@ public:
                                 MachineBasicBlock *FBB,
                                 const SmallVectorImpl<MachineOperand> &Cond,
                                 DebugLoc DL) const;
+
+  // Select analysis.
+  virtual bool canInsertSelect(const MachineBasicBlock&,
+                               const SmallVectorImpl<MachineOperand> &Cond,
+                               unsigned, unsigned, int&, int&, int&) const;
+  virtual void insertSelect(MachineBasicBlock &MBB,
+                            MachineBasicBlock::iterator MI, DebugLoc DL,
+                            unsigned DstReg,
+                            const SmallVectorImpl<MachineOperand> &Cond,
+                            unsigned TrueReg, unsigned FalseReg) const;
+
   virtual void copyPhysReg(MachineBasicBlock &MBB,
                            MachineBasicBlock::iterator I, DebugLoc DL,
                            unsigned DestReg, unsigned SrcReg,

lib/Target/PowerPC/PPCTargetMachine.cpp

@@ -86,7 +86,12 @@ public:
     return getTM<PPCTargetMachine>();
   }
 
+  const PPCSubtarget &getPPCSubtarget() const {
+    return *getPPCTargetMachine().getSubtargetImpl();
+  }
+
   virtual bool addPreRegAlloc();
+  virtual bool addILPOpts();
   virtual bool addInstSelector();
   virtual bool addPreEmitPass();
 };
@@ -103,6 +108,15 @@ bool PPCPassConfig::addPreRegAlloc() {
   return false;
 }
 
+bool PPCPassConfig::addILPOpts() {
+  if (getPPCSubtarget().hasISEL()) {
+    addPass(&EarlyIfConverterID);
+    return true;
+  }
+
+  return false;
+}
+
 bool PPCPassConfig::addInstSelector() {
   // Install an instruction selector.
   addPass(createPPCISelDag(getPPCTargetMachine()));

test/CodeGen/PowerPC/ifcvt.ll

@@ -0,0 +1,34 @@
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 -verify-machineinstrs | FileCheck %s
+target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+define i32 @test(i32 %a, i32 %b, i32 %c, i32 %d) {
+entry:
+  %sext82 = shl i32 %d, 16
+  %conv29 = ashr exact i32 %sext82, 16
+  %cmp = icmp slt i32 %sext82, 0
+  br i1 %cmp, label %cond.true, label %cond.false
+
+cond.true:                                        ; preds = %sw.epilog
+  %and33 = and i32 %conv29, 32767
+  %sub34 = sub nsw i32 %a, %and33
+  br label %cond.end
+
+cond.false:                                       ; preds = %sw.epilog
+  %add37 = add nsw i32 %conv29, %a
+  br label %cond.end
+
+; CHECK: @test
+; CHECK: add [[REG:[0-9]+]], 
+; CHECK: subf [[REG2:[0-9]+]],
+; CHECK: isel {{[0-9]+}}, [[REG]], [[REG2]],
+
+cond.end:                                         ; preds = %cond.false, %cond.true
+  %cond = phi i32 [ %sub34, %cond.true ], [ %add37, %cond.false ]
+  %sext83 = shl i32 %cond, 16
+  %conv39 = ashr exact i32 %sext83, 16
+  %add41 = sub i32 %b, %a
+  %sub43 = add i32 %add41, %conv39
+  ret i32 %sub43
+}
+