Subzero: Use std::vector<> instead of std::list for live range segments.

src/IceDefs.h

@@ -23,7 +23,6 @@
 #include <limits>
 #include <list>
 #include <map>
-#include <set>
 #include <string>
 #include <vector>
 #include "llvm/ADT/ArrayRef.h"

src/IceOperand.cpp

@@ -33,37 +33,6 @@ bool operator==(const RegWeight &A, const RegWeight &B) {
 }
 
 void LiveRange::addSegment(InstNumberT Start, InstNumberT End) {
-#ifdef USE_SET
-  RangeElementType Element(Start, End);
-  RangeType::iterator Next = Range.lower_bound(Element);
-  assert(Next == Range.upper_bound(Element)); // Element not already present
-
-  // Beginning of code that merges contiguous segments.  TODO: change
-  // "if(true)" to "if(false)" to see if this extra optimization code
-  // gives any performance gain, or is just destabilizing.
-  if (true) {
-    RangeType::iterator FirstDelete = Next;
-    RangeType::iterator Prev = Next;
-    bool hasPrev = (Next != Range.begin());
-    bool hasNext = (Next != Range.end());
-    if (hasPrev)
-      --Prev;
-    // See if Element and Next should be joined.
-    if (hasNext && End == Next->first) {
-      Element.second = Next->second;
-      ++Next;
-    }
-    // See if Prev and Element should be joined.
-    if (hasPrev && Prev->second == Start) {
-      Element.first = Prev->first;
-      FirstDelete = Prev;
-    }
-    Range.erase(FirstDelete, Next);
-  }
-  // End of code that merges contiguous segments.
-
-  Range.insert(Next, Element);
-#else
   if (Range.empty()) {
     Range.push_back(RangeElementType(Start, End));
     return;
@@ -71,7 +40,10 @@ void LiveRange::addSegment(InstNumberT Start, InstNumberT End) {
   // Special case for faking in-arg liveness.
   if (End < Range.front().first) {
     assert(Start < 0);
-    Range.push_front(RangeElementType(Start, End));
+    // 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;
@@ -82,7 +54,6 @@ void LiveRange::addSegment(InstNumberT Start, InstNumberT End) {
     return;
   }
   Range.push_back(RangeElementType(Start, End));
-#endif
 }
 
 // Returns true if this live range ends before Other's live range

src/IceOperand.h

@@ -326,6 +326,13 @@ bool operator==(const RegWeight &A, const RegWeight &B);
 class LiveRange {
 public:
   LiveRange() : Weight(0) {}
+  // Special constructor for building a kill set.  The advantage is
+  // that we can reserve the right amount of space in advance.
+  LiveRange(const std::vector<InstNumberT> &Kills) : Weight(0) {
+    Range.reserve(Kills.size());
+    for (InstNumberT I : Kills)
+      addSegment(I, I);
+  }
   LiveRange(const LiveRange &) = default;
   LiveRange &operator=(const LiveRange &) = default;
 
@@ -353,19 +360,9 @@ public:
   void addWeight(uint32_t Delta) { Weight.addWeight(Delta); }
   void dump(Ostream &Str) const;
 
-  // Defining USE_SET uses std::set to hold the segments instead of
-  // std::list.  Using std::list will be slightly faster, but is more
-  // restrictive because new segments cannot be added in the middle.
-
-  //#define USE_SET
-
 private:
   typedef std::pair<InstNumberT, InstNumberT> RangeElementType;
-#ifdef USE_SET
-  typedef std::set<RangeElementType> RangeType;
-#else
-  typedef std::list<RangeElementType> RangeType;
-#endif
+  typedef std::vector<RangeElementType> RangeType;
   RangeType Range;
   RegWeight Weight;
   // TrimmedBegin is an optimization for the overlaps() computation.

src/IceRegAlloc.cpp

@@ -268,9 +268,7 @@ void LinearScan::scan(const llvm::SmallBitVector &RegMaskFull) {
   VariablesMetadata *VMetadata = Func->getVMetadata();
 
   // Build a LiveRange representing the Kills list.
-  LiveRange KillsRange;
-  for (InstNumberT I : Kills)
-    KillsRange.addSegment(I, I);
+  LiveRange KillsRange(Kills);
   KillsRange.untrim();
 
   // RegUses[I] is the number of live ranges (variables) that register