Fix failing test cases with joined live intervals. It turns out that

when joining we need to check if we overlap with the second interval
or any of its aliases.

Also make joining intervals the default.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10973 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveIntervalAnalysis.h

@@ -162,6 +162,8 @@ namespace llvm {
                                        MachineBasicBlock::iterator mi,
                                        unsigned reg);
 
+        bool overlapsAliases(const Interval& lhs, const Interval& rhs) const;
+
         unsigned getInstructionIndex(MachineInstr* instr) const;
 
         void printRegName(unsigned reg) const;

include/llvm/CodeGen/LiveIntervals.h

@@ -162,6 +162,8 @@ namespace llvm {
                                        MachineBasicBlock::iterator mi,
                                        unsigned reg);
 
+        bool overlapsAliases(const Interval& lhs, const Interval& rhs) const;
+
         unsigned getInstructionIndex(MachineInstr* instr) const;
 
         void printRegName(unsigned reg) const;