TargetRegisterInfo: Provide a way to check assigned registers in getRegAllocationHints()

Pass a const reference to LiveRegMatrix to getRegAllocationHints()
because some targets can prodive better hints if they can test whether a
physreg has been used for register allocation yet.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242340 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetRegisterInfo.h

@@ -32,6 +32,7 @@ class RegScavenger;
 template<class T> class SmallVectorImpl;
 class VirtRegMap;
 class raw_ostream;
+class LiveRegMatrix;
 
 class TargetRegisterClass {
 public:
@@ -709,7 +710,9 @@ public:
                                      ArrayRef<MCPhysReg> Order,
                                      SmallVectorImpl<MCPhysReg> &Hints,
                                      const MachineFunction &MF,
-                                     const VirtRegMap *VRM = nullptr) const;
+                                     const VirtRegMap *VRM = nullptr,
+                                     const LiveRegMatrix *Matrix = nullptr)
+    const;
 
   /// updateRegAllocHint - A callback to allow target a chance to update
   /// register allocation hints when a register is "changed" (e.g. coalesced)