[SystemZ] Improve emitSelect()

Merge more Select pseudo instructions in emitSelect() by allowing other
instructions between them as long as they do not clobber CC.

Debug value instructions are now moved down to below the new PHIs instead of
erasing them.

Review: Ulrich Weigand
https://reviews.llvm.org/D67619

llvm-svn: 372873

1 files changed, 58 insertions, 33 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
index 6a0f59ef56a..ba79ec2986a 100644
--- a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -6563,19 +6563,17 @@ static bool isSelectPseudo(MachineInstr &MI) {
 
 // Helper function, which inserts PHI functions into SinkMBB:
 //   %Result(i) = phi [ %FalseValue(i), FalseMBB ], [ %TrueValue(i), TrueMBB ],
-// where %FalseValue(i) and %TrueValue(i) are taken from the consequent Selects
-// in [MIItBegin, MIItEnd) range.
-static void createPHIsForSelects(MachineBasicBlock::iterator MIItBegin,
-                                 MachineBasicBlock::iterator MIItEnd,
+// where %FalseValue(i) and %TrueValue(i) are taken from Selects.
+static void createPHIsForSelects(SmallVector<MachineInstr*, 8> &Selects,
                                  MachineBasicBlock *TrueMBB,
                                  MachineBasicBlock *FalseMBB,
                                  MachineBasicBlock *SinkMBB) {
   MachineFunction *MF = TrueMBB->getParent();
   const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
 
-  unsigned CCValid = MIItBegin->getOperand(3).getImm();
-  unsigned CCMask = MIItBegin->getOperand(4).getImm();
-  DebugLoc DL = MIItBegin->getDebugLoc();
+  MachineInstr *FirstMI = Selects.front();
+  unsigned CCValid = FirstMI->getOperand(3).getImm();
+  unsigned CCMask = FirstMI->getOperand(4).getImm();
 
   MachineBasicBlock::iterator SinkInsertionPoint = SinkMBB->begin();
 
@@ -6587,16 +6585,15 @@ static void createPHIsForSelects(MachineBasicBlock::iterator MIItBegin,
   // destination registers, and the registers that went into the PHI.
   DenseMap<unsigned, std::pair<unsigned, unsigned>> RegRewriteTable;
 
-  for (MachineBasicBlock::iterator MIIt = MIItBegin; MIIt != MIItEnd;
-       MIIt = skipDebugInstructionsForward(++MIIt, MIItEnd)) {
-    Register DestReg = MIIt->getOperand(0).getReg();
-    Register TrueReg = MIIt->getOperand(1).getReg();
-    Register FalseReg = MIIt->getOperand(2).getReg();
+  for (auto MI : Selects) {
+    Register DestReg = MI->getOperand(0).getReg();
+    Register TrueReg = MI->getOperand(1).getReg();
+    Register FalseReg = MI->getOperand(2).getReg();
 
     // If this Select we are generating is the opposite condition from
     // the jump we generated, then we have to swap the operands for the
     // PHI that is going to be generated.
-    if (MIIt->getOperand(4).getImm() == (CCValid ^ CCMask))
+    if (MI->getOperand(4).getImm() == (CCValid ^ CCMask))
       std::swap(TrueReg, FalseReg);
 
     if (RegRewriteTable.find(TrueReg) != RegRewriteTable.end())
@@ -6605,6 +6602,7 @@ static void createPHIsForSelects(MachineBasicBlock::iterator MIItBegin,
     if (RegRewriteTable.find(FalseReg) != RegRewriteTable.end())
       FalseReg = RegRewriteTable[FalseReg].second;
 
+    DebugLoc DL = MI->getDebugLoc();
     BuildMI(*SinkMBB, SinkInsertionPoint, DL, TII->get(SystemZ::PHI), DestReg)
       .addReg(TrueReg).addMBB(TrueMBB)
       .addReg(FalseReg).addMBB(FalseMBB);
@@ -6620,36 +6618,61 @@ static void createPHIsForSelects(MachineBasicBlock::iterator MIItBegin,
 MachineBasicBlock *
 SystemZTargetLowering::emitSelect(MachineInstr &MI,
                                   MachineBasicBlock *MBB) const {
+  assert(isSelectPseudo(MI) && "Bad call to emitSelect()");
   const SystemZInstrInfo *TII =
       static_cast<const SystemZInstrInfo *>(Subtarget.getInstrInfo());
 
   unsigned CCValid = MI.getOperand(3).getImm();
   unsigned CCMask = MI.getOperand(4).getImm();
-  DebugLoc DL = MI.getDebugLoc();
 
   // If we have a sequence of Select* pseudo instructions using the
   // same condition code value, we want to expand all of them into
   // a single pair of basic blocks using the same condition.
-  MachineInstr *LastMI = &MI;
-  MachineBasicBlock::iterator NextMIIt = skipDebugInstructionsForward(
-      std::next(MachineBasicBlock::iterator(MI)), MBB->end());
-
-  if (isSelectPseudo(MI))
-    while (NextMIIt != MBB->end() && isSelectPseudo(*NextMIIt) &&
-           NextMIIt->getOperand(3).getImm() == CCValid &&
-           (NextMIIt->getOperand(4).getImm() == CCMask ||
-            NextMIIt->getOperand(4).getImm() == (CCValid ^ CCMask))) {
-      LastMI = &*NextMIIt;
-      NextMIIt = skipDebugInstructionsForward(++NextMIIt, MBB->end());
+  SmallVector<MachineInstr*, 8> Selects;
+  SmallVector<MachineInstr*, 8> DbgValues;
+  Selects.push_back(&MI);
+  unsigned Count = 0;
+  for (MachineBasicBlock::iterator NextMIIt =
+         std::next(MachineBasicBlock::iterator(MI));
+       NextMIIt != MBB->end(); ++NextMIIt) {
+    if (NextMIIt->definesRegister(SystemZ::CC))
+      break;
+    if (isSelectPseudo(*NextMIIt)) {
+      assert(NextMIIt->getOperand(3).getImm() == CCValid &&
+             "Bad CCValid operands since CC was not redefined.");
+      if (NextMIIt->getOperand(4).getImm() == CCMask ||
+          NextMIIt->getOperand(4).getImm() == (CCValid ^ CCMask)) {
+        Selects.push_back(&*NextMIIt);
+        continue;
+      }
+      break;
     }
+    bool User = false;
+    for (auto SelMI : Selects)
+      if (NextMIIt->readsVirtualRegister(SelMI->getOperand(0).getReg())) {
+        User = true;
+        break;
+      }
+    if (NextMIIt->isDebugInstr()) {
+      if (User) {
+        assert(NextMIIt->isDebugValue() && "Unhandled debug opcode.");
+        DbgValues.push_back(&*NextMIIt);
+      }
+    }
+    else if (User || ++Count > 20)
+      break;
+  }
 
+  MachineInstr *LastMI = Selects.back();
+  bool CCKilled =
+      (LastMI->killsRegister(SystemZ::CC) || checkCCKill(*LastMI, MBB));
   MachineBasicBlock *StartMBB = MBB;
-  MachineBasicBlock *JoinMBB  = splitBlockBefore(MI, MBB);
+  MachineBasicBlock *JoinMBB  = splitBlockAfter(LastMI, MBB);
   MachineBasicBlock *FalseMBB = emitBlockAfter(StartMBB);
 
   // Unless CC was killed in the last Select instruction, mark it as
   // live-in to both FalseMBB and JoinMBB.
-  if (!LastMI->killsRegister(SystemZ::CC) && !checkCCKill(*LastMI, JoinMBB)) {
+  if (!CCKilled) {
     FalseMBB->addLiveIn(SystemZ::CC);
     JoinMBB->addLiveIn(SystemZ::CC);
   }
@@ -6658,7 +6681,7 @@ SystemZTargetLowering::emitSelect(MachineInstr &MI,
   //   BRC CCMask, JoinMBB
   //   # fallthrough to FalseMBB
   MBB = StartMBB;
-  BuildMI(MBB, DL, TII->get(SystemZ::BRC))
+  BuildMI(MBB, MI.getDebugLoc(), TII->get(SystemZ::BRC))
     .addImm(CCValid).addImm(CCMask).addMBB(JoinMBB);
   MBB->addSuccessor(JoinMBB);
   MBB->addSuccessor(FalseMBB);
@@ -6672,12 +6695,14 @@ SystemZTargetLowering::emitSelect(MachineInstr &MI,
   //   %Result = phi [ %FalseReg, FalseMBB ], [ %TrueReg, StartMBB ]
   //  ...
   MBB = JoinMBB;
-  MachineBasicBlock::iterator MIItBegin = MachineBasicBlock::iterator(MI);
-  MachineBasicBlock::iterator MIItEnd = skipDebugInstructionsForward(
-      std::next(MachineBasicBlock::iterator(LastMI)), MBB->end());
-  createPHIsForSelects(MIItBegin, MIItEnd, StartMBB, FalseMBB, MBB);
+  createPHIsForSelects(Selects, StartMBB, FalseMBB, MBB);
+  for (auto SelMI : Selects)
+    SelMI->eraseFromParent();
+
+  MachineBasicBlock::iterator InsertPos = MBB->getFirstNonPHI();
+  for (auto DbgMI : DbgValues)
+    MBB->splice(InsertPos, StartMBB, DbgMI);
 
-  MBB->erase(MIItBegin, MIItEnd);
   return JoinMBB;
 }