MachineBasicBlock: Cleanup computeRegisterLiveness()

- Clean documentation comment
- Change the API to accept an iterator so you can actually pass
  MachineBasicBlock::end() now.
- Add more "const".

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238288 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineBasicBlock.h

@@ -633,17 +633,18 @@ public:
                          ///< neighborhood.
   };
 
-  /// computeRegisterLiveness - Return whether (physical) register \c Reg
+  /// Return whether (physical) register \p Reg has been <def>ined and not
-  /// has been <def>ined and not <kill>ed as of just before \c MI.
+  /// <kill>ed as of just before \p Before.
   ///
-  /// Search is localised to a neighborhood of
+  /// Search is localised to a neighborhood of \p Neighborhood instructions
-  /// \c Neighborhood instructions before (searching for defs or kills) and
+  /// before (searching for defs or kills) and \p Neighborhood instructions
-  /// Neighborhood instructions after (searching just for defs) MI.
+  /// after (searching just for defs) \p Before.
   ///
-  /// \c Reg must be a physical register.
+  /// \p Reg must be a physical register.
   LivenessQueryResult computeRegisterLiveness(const TargetRegisterInfo *TRI,
-                                              unsigned Reg, MachineInstr *MI,
+                                              unsigned Reg,
-                                              unsigned Neighborhood=10);
+                                              const_iterator Before,
+                                              unsigned Neighborhood=10) const;
 
   // Debugging methods.
   void dump() const;

lib/CodeGen/MachineBasicBlock.cpp

@@ -1129,21 +1129,19 @@ getWeightIterator(MachineBasicBlock::const_succ_iterator I) const {
 /// instructions after (searching just for defs) MI.
 MachineBasicBlock::LivenessQueryResult
 MachineBasicBlock::computeRegisterLiveness(const TargetRegisterInfo *TRI,
-                                           unsigned Reg, MachineInstr *MI,
+                                           unsigned Reg, const_iterator Before,
-                                           unsigned Neighborhood) {
+                                           unsigned Neighborhood) const {
   unsigned N = Neighborhood;
-  MachineBasicBlock *MBB = MI->getParent();
 
-  // Start by searching backwards from MI, looking for kills, reads or defs.
+  // Start by searching backwards from Before, looking for kills, reads or defs.
-
+  const_iterator I(Before);
-  MachineBasicBlock::iterator I(MI);
   // If this is the first insn in the block, don't search backwards.
-  if (I != MBB->begin()) {
+  if (I != begin()) {
     do {
       --I;
 
       MachineOperandIteratorBase::PhysRegInfo Analysis =
-        MIOperands(I).analyzePhysReg(Reg, TRI);
+        ConstMIOperands(I).analyzePhysReg(Reg, TRI);
 
       if (Analysis.Defines)
         // Outputs happen after inputs so they take precedence if both are
@@ -1158,15 +1156,15 @@ MachineBasicBlock::computeRegisterLiveness(const TargetRegisterInfo *TRI,
         // Defined or read without a previous kill - live.
         return Analysis.Reads ? LQR_Live : LQR_OverlappingLive;
 
-    } while (I != MBB->begin() && --N > 0);
+    } while (I != begin() && --N > 0);
   }
 
   // Did we get to the start of the block?
-  if (I == MBB->begin()) {
+  if (I == begin()) {
     // If so, the register's state is definitely defined by the live-in state.
     for (MCRegAliasIterator RAI(Reg, TRI, /*IncludeSelf=*/true);
          RAI.isValid(); ++RAI) {
-      if (MBB->isLiveIn(*RAI))
+      if (isLiveIn(*RAI))
         return (*RAI == Reg) ? LQR_Live : LQR_OverlappingLive;
     }
 
@@ -1175,13 +1173,13 @@ MachineBasicBlock::computeRegisterLiveness(const TargetRegisterInfo *TRI,
 
   N = Neighborhood;
 
-  // Try searching forwards from MI, looking for reads or defs.
+  // Try searching forwards from Before, looking for reads or defs.
-  I = MachineBasicBlock::iterator(MI);
+  I = const_iterator(Before);
   // If this is the last insn in the block, don't search forwards.
-  if (I != MBB->end()) {
+  if (I != end()) {
-    for (++I; I != MBB->end() && N > 0; ++I, --N) {
+    for (++I; I != end() && N > 0; ++I, --N) {
       MachineOperandIteratorBase::PhysRegInfo Analysis =
-        MIOperands(I).analyzePhysReg(Reg, TRI);
+        ConstMIOperands(I).analyzePhysReg(Reg, TRI);
 
       if (Analysis.ReadsOverlap)
         // Used, therefore must have been live.