[regalloc] Add a couple of dump routines for ease of debugging [NFC]

lib/CodeGen/SpillPlacement.cpp

@@ -377,3 +377,27 @@ SpillPlacement::finish() {
   ActiveNodes = nullptr;
   return Perfect;
 }
+
+void SpillPlacement::BlockConstraint::print(raw_ostream &OS) const {
+  auto toString = [](BorderConstraint C) -> StringRef {
+    switch(C) {
+    case DontCare: return "DontCare";
+    case PrefReg: return "PrefReg";
+    case PrefSpill: return "PrefSpill";
+    case PrefBoth: return "PrefBoth";
+    case MustSpill: return "MustSpill";
+    default:
+      llvm_unreachable("uncovered switch");
+    };
+  };
+
+  dbgs() << "{" << Number << ", "
+         << toString(Entry) << ", "
+         << toString(Exit) << ", "
+         << (ChangesValue ? "changes" : "no change") << "}";
+}
+
+void SpillPlacement::BlockConstraint::dump() const {
+  print(dbgs());
+  dbgs() << "\n";
+}

lib/CodeGen/SpillPlacement.h

@@ -95,6 +95,9 @@ public:
     /// the block has a non-PHI def.  When this is false, a live-in value on
     /// the stack can be live-out on the stack without inserting a spill.
     bool ChangesValue;
+
+    void print(raw_ostream &OS) const;
+    void dump() const;
   };
 
   /// prepare - Reset state and prepare for a new spill placement computation.

lib/CodeGen/SplitKit.cpp

@@ -1812,3 +1812,16 @@ void SplitEditor::splitRegOutBlock(const SplitAnalysis::BlockInfo &BI,
   SlotIndex From = enterIntvBefore(std::min(Idx, BI.FirstInstr));
   useIntv(From, Idx);
 }
+
+void SplitAnalysis::BlockInfo::print(raw_ostream &OS) const {
+  OS << "{" << printMBBReference(*MBB) << ", "
+     << "uses " << FirstInstr << " to " << LastInstr << ", "
+     << "1st def " << FirstDef << ", "
+     << (LiveIn ? "live in" : "dead in") << ", "
+     << (LiveOut ? "live out" : "dead out") << "}";
+}
+
+void SplitAnalysis::BlockInfo::dump() const {
+  print(dbgs());
+  dbgs() << "\n";
+}

lib/CodeGen/SplitKit.h

@@ -131,6 +131,9 @@ public:
     bool isOneInstr() const {
       return SlotIndex::isSameInstr(FirstInstr, LastInstr);
     }
+
+    void print(raw_ostream &OS) const;
+    void dump() const;
   };
 
 private: