[MachineOutliner][NFC] Change getMachineOutlinerMBBFlags to isMBBSafeToOutlineFrom

Instead of returning Flags, return true if the MBB is safe to outline from.

This lets us check for unsafe situations, like say, in AArch64, X17 is live
across a MBB without being defined in that MBB. In that case, there's no point
in performing an instruction mapping.

llvm-svn: 346718

llvm/include/llvm/CodeGen/TargetInstrInfo.h

@@ -1635,10 +1635,11 @@ public:
         "Target didn't implement TargetInstrInfo::getOutliningType!");
   }
 
-  /// Returns target-defined flags defining properties of the MBB for
-  /// the outliner.
-  virtual unsigned getMachineOutlinerMBBFlags(MachineBasicBlock &MBB) const {
-    return 0x0;
+  /// Optional target hook that returns true if \p MBB is safe to outline from,
+  /// and returns any target-specific information in \p Flags.
+  virtual bool isMBBSafeToOutlineFrom(MachineBasicBlock &MBB,
+                                      unsigned &Flags) const {
+    return true;
   }
 
   /// Insert a custom frame for outlined functions.

llvm/lib/CodeGen/MachineOutliner.cpp

@@ -742,7 +742,12 @@ struct InstructionMapper {
   /// \param TII \p TargetInstrInfo for the function.
   void convertToUnsignedVec(MachineBasicBlock &MBB,
                             const TargetInstrInfo &TII) {
-    unsigned Flags = TII.getMachineOutlinerMBBFlags(MBB);
+    unsigned Flags;
+
+    // Don't even map in this case.
+    if (!TII.isMBBSafeToOutlineFrom(MBB, Flags))
+      return;
+
     MachineBasicBlock::iterator It = MBB.begin();
 
     // The number of instructions in this block that will be considered for

llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

@@ -5286,29 +5286,44 @@ bool AArch64InstrInfo::isFunctionSafeToOutlineFrom(
   return true;
 }
 
-unsigned
-AArch64InstrInfo::getMachineOutlinerMBBFlags(MachineBasicBlock &MBB) const {
-  unsigned Flags = 0x0;
+bool AArch64InstrInfo::isMBBSafeToOutlineFrom(MachineBasicBlock &MBB,
+                                              unsigned &Flags) const {
+  // Check if LR is available through all of the MBB. If it's not, then set
+  // a flag.
+  assert(MBB.getParent()->getRegInfo().tracksLiveness() &&
+         "Suitable Machine Function for outlining must track liveness");
+  LiveRegUnits ModifiedRegUnits(getRegisterInfo());
+  LiveRegUnits UsedRegUnits(getRegisterInfo());
+  ModifiedRegUnits.addLiveOuts(MBB);
+  UsedRegUnits.addLiveOuts(MBB);
+  const TargetRegisterInfo *TRI = &getRegisterInfo();
+
+  std::for_each(MBB.rbegin(), MBB.rend(),
+                [&ModifiedRegUnits, &UsedRegUnits, &TRI](MachineInstr &MI) {
+                  LiveRegUnits::accumulateUsedDefed(MI, ModifiedRegUnits,
+                                                    UsedRegUnits, TRI);
+                });
+
+  // If one of these registers is live out of the MBB, but not modified in the
+  // MBB, then we can't outline.
+  if ((ModifiedRegUnits.available(AArch64::W16) &&
+       !UsedRegUnits.available(AArch64::W16)) ||
+      (ModifiedRegUnits.available(AArch64::W17) &&
+       !UsedRegUnits.available(AArch64::W17)) ||
+      (ModifiedRegUnits.available(AArch64::NZCV) &&
+       !UsedRegUnits.available(AArch64::NZCV)))
+    return false;
+
   // Check if there's a call inside this MachineBasicBlock. If there is, then
   // set a flag.
   if (any_of(MBB, [](MachineInstr &MI) { return MI.isCall(); }))
     Flags |= MachineOutlinerMBBFlags::HasCalls;
 
-  // Check if LR is available through all of the MBB. If it's not, then set
-  // a flag.
-  assert(MBB.getParent()->getRegInfo().tracksLiveness() &&
-         "Suitable Machine Function for outlining must track liveness");
-  LiveRegUnits LRU(getRegisterInfo());
-  LRU.addLiveOuts(MBB);
+  if (!ModifiedRegUnits.available(AArch64::LR) ||
+      !UsedRegUnits.available(AArch64::LR))
+    Flags |= MachineOutlinerMBBFlags::LRUnavailableSomewhere;
 
-  std::for_each(MBB.rbegin(),
-                MBB.rend(),
-                [&LRU](MachineInstr &MI) { LRU.accumulate(MI); });
-
-  if (!LRU.available(AArch64::LR))
-      Flags |= MachineOutlinerMBBFlags::LRUnavailableSomewhere;
-
-  return Flags;
+  return true;
 }
 
 outliner::InstrType

llvm/lib/Target/AArch64/AArch64InstrInfo.h

@@ -246,7 +246,8 @@ public:
       std::vector<outliner::Candidate> &RepeatedSequenceLocs) const override;
   outliner::InstrType
   getOutliningType(MachineBasicBlock::iterator &MIT, unsigned Flags) const override;
-  unsigned getMachineOutlinerMBBFlags(MachineBasicBlock &MBB) const override;
+  bool isMBBSafeToOutlineFrom(MachineBasicBlock &MBB,
+                              unsigned &Flags) const override;
   void buildOutlinedFrame(MachineBasicBlock &MBB, MachineFunction &MF,
                           const outliner::OutlinedFunction &OF) const override;
   MachineBasicBlock::iterator