Now that I am told MachineRegisterInfo also tracks physical register uses / defs, I can do away with the horribleness I introduced a while back. It's impossible to detect if there is any use of a physical register below an instruction (and before any def of the register) with some cheap book keeping.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@49105 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveVariables.h

@@ -31,11 +31,13 @@
 
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
 
 namespace llvm {
 
+class MachineRegisterInfo;
 class TargetRegisterInfo;
 
 class LiveVariables : public MachineFunctionPass {
@@ -128,6 +130,8 @@ private:
 private:   // Intermediate data structures
   MachineFunction *MF;
 
+  MachineRegisterInfo* MRI;
+
   const TargetRegisterInfo *TRI;
 
   // PhysRegInfo - Keep track of which instruction was the last def/use of a
@@ -152,6 +156,10 @@ private:   // Intermediate data structures
 
   SmallVector<unsigned, 4> *PHIVarInfo;
 
+  // DistanceMap - Keep track the distance of a MI from the start of the
+  // current basic block.
+  DenseMap<MachineInstr*, unsigned> DistanceMap;
+
   void addRegisterKills(unsigned Reg, MachineInstr *MI,
                         SmallSet<unsigned, 4> &SubKills);