Keep track of phi join registers explicitly in LiveVariables.

Previously, LiveIntervalAnalysis would infer phi joins by looking for multiply
defined registers. That doesn't work if the phi join is implicitly defined in
all but one of the predecessors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96994 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveVariables.cpp

@@ -510,6 +510,7 @@ bool LiveVariables::runOnMachineFunction(MachineFunction &mf) {
   PHIVarInfo = new SmallVector<unsigned, 4>[MF->getNumBlockIDs()];
   std::fill(PhysRegDef,  PhysRegDef  + NumRegs, (MachineInstr*)0);
   std::fill(PhysRegUse,  PhysRegUse  + NumRegs, (MachineInstr*)0);
+  PHIJoins.clear();
 
   /// Get some space for a respectable number of registers.
   VirtRegInfo.resize(64);