Subzero: Clean up live range construction.

src/IceOperand.cpp

 //===- subzero/src/IceOperand.cpp - High-level operand implementation -----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the Operand class and its target-independent
@@ skipping 15 matching lines @@
 
 bool operator<(const RegWeight &A, const RegWeight &B) {
   return A.getWeight() < B.getWeight();
 }
 bool operator<=(const RegWeight &A, const RegWeight &B) { return !(B < A); }
 bool operator==(const RegWeight &A, const RegWeight &B) {
   return !(B < A) && !(A < B);
 }
 
 void LiveRange::addSegment(InstNumberT Start, InstNumberT End) {
-  if (Range.empty()) {
-    Range.push_back(RangeElementType(Start, End));
-    return;
-  }
-  // Special case for faking in-arg liveness.
-  if (End < Range.front().first) {
-    assert(Start < 0);
-    // This is inefficient with Range as a std::vector, but there are
-    // generally very few arguments compared to the total number of
-    // variables with non-empty live ranges.
-    Range.insert(Range.begin(), RangeElementType(Start, End));
-    return;
-  }
-  InstNumberT CurrentEnd = Range.back().second;
-  assert(Start >= CurrentEnd);
-  // Check for merge opportunity.
-  if (Start == CurrentEnd) {
-    Range.back().second = End;
-    return;
+  if (!Range.empty()) {
+    // Check for merge opportunity.
+    InstNumberT CurrentEnd = Range.back().second;
+    assert(Start >= CurrentEnd);
+    if (Start == CurrentEnd) {
+      Range.back().second = End;
+      return;
+    }
   }
   Range.push_back(RangeElementType(Start, End));
 }
 
 // Returns true if this live range ends before Other's live range
 // starts.  This means that the highest instruction number in this
 // live range is less than or equal to the lowest instruction number
 // of the Other live range.
 bool LiveRange::endsBefore(const LiveRange &Other) const {
   // Neither range should be empty, but let's be graceful.
@@ skipping 426 matching lines @@
   if (!ALLOW_DUMP)
     return Str;
   if (W.getWeight() == RegWeight::Inf)
     Str << "Inf";
   else
     Str << W.getWeight();
   return Str;
 }
 
 } // end of namespace Ice