remove pseudo optimization from Segment definition

in addition, allow printing of empty LR

Author: aparshin-intel

IGC/VectorCompiler/lib/GenXCodeGen/GenXLiveness.cpp

@@ -1767,14 +1767,20 @@ unsigned LiveRange::getLength(bool WithWeak) const {
  */
 void LiveRange::print(raw_ostream &OS) const
 {
+  if (Values.empty()) {
+    OS << "Empty LR";
+    return;
+  }
+
   auto vi = Values.begin(), ve = Values.end();
-  IGC_ASSERT(vi != ve);
-  for (;;) {
+  bool AllNamesPrinted = false;
+  do {
     vi->printName(OS);
-    if (++vi == ve)
-      break;
-    OS << ",";
-  }
+    AllNamesPrinted = (++vi == ve);
+    if (!AllNamesPrinted)
+      OS << ",";
+  } while (!AllNamesPrinted);
+
   OS << ":";
   printSegments(OS);
   const char *Cat = "???";
@@ -1805,6 +1811,7 @@ void LiveRange::printSegments(raw_ostream &OS) const
     switch (ri->Strength) {
       case Segment::WEAK: OS << "w"; break;
       case Segment::PHICPY: OS << "ph"; break;
+      case Segment::STRONG: /* do nothing */ break;
     }
     OS << ri->getStart() << "," << ri->getEnd() << ")";
   }

IGC/VectorCompiler/lib/GenXCodeGen/GenXLiveness.h

@@ -295,15 +295,15 @@ class AssertingSV {
 // Segment : a single range of instruction numbers in which a value is
 // live
 struct Segment {
-  enum { WEAK, PHICPY, STRONG };
-  unsigned Strength : 2; // whether it is a weak or phicpy or strong segment
+  enum SegmentType : unsigned char { WEAK, PHICPY, STRONG };
+  SegmentType Strength;
 
 private:
-  unsigned Start : 30; // inclusive start of range
-  unsigned End : 30;   // exclusive end of range
+  unsigned Start;
+  unsigned End;
 public:
   Segment() :  Strength(STRONG), Start(0), End(0) {}
-  Segment(unsigned S, unsigned E, unsigned Strength = STRONG)
+  Segment(unsigned S, unsigned E, SegmentType Strength = STRONG)
       : Strength(Strength) {
     IGC_ASSERT(E >= S);
     Start = S;