LiveRangeCalc: Slightly improve map usage; NFC

- DenseMap should be faster than std::map
- Use the `InsertRes = insert() if (!InsertRes.inserted)` pattern rather
  than the `if (!X.contains(...)) { X.insert(...); }` to save one map
  lookup.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306436 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveRangeCalc.cpp

@@ -24,7 +24,7 @@ void LiveRangeCalc::resetLiveOutMap() {
   unsigned NumBlocks = MF->getNumBlockIDs();
   Seen.clear();
   Seen.resize(NumBlocks);
-  EntryInfoMap.clear();
+  EntryInfos.clear();
   Map.resize(NumBlocks);
 }
 
@@ -433,15 +433,18 @@ bool LiveRangeCalc::findReachingDefs(LiveRange &LR, MachineBasicBlock &UseMBB,
   }
 
   // Prepare the defined/undefined bit vectors.
-  auto EF = EntryInfoMap.find(&LR);
-  if (EF == EntryInfoMap.end()) {
+  EntryInfoMap::iterator Entry;
+  bool DidInsert;
+  std::tie(Entry, DidInsert) = EntryInfos.insert(
+      std::make_pair(&LR, std::make_pair(BitVector(), BitVector())));
+  if (DidInsert) {
+    // Initialize newly inserted entries.
     unsigned N = MF->getNumBlockIDs();
-    EF = EntryInfoMap.insert({&LR, {BitVector(), BitVector()}}).first;
-    EF->second.first.resize(N);
-    EF->second.second.resize(N);
+    Entry->second.first.resize(N);
+    Entry->second.second.resize(N);
   }
-  BitVector &DefOnEntry = EF->second.first;
-  BitVector &UndefOnEntry = EF->second.second;
+  BitVector &DefOnEntry = Entry->second.first;
+  BitVector &UndefOnEntry = Entry->second.second;
 
   // Multiple values were found, so transfer the work list to the LiveIn array
   // where UpdateSSA will use it as a work list.

lib/CodeGen/LiveRangeCalc.h

@@ -24,6 +24,7 @@
 
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/IndexedMap.h"
 #include "llvm/CodeGen/LiveInterval.h"
 
@@ -65,7 +66,8 @@ class LiveRangeCalc {
   /// registers do not overlap), but the defined/undefined information must
   /// be kept separate for each individual range.
   /// By convention, EntryInfoMap[&LR] = { Defined, Undefined }.
-  std::map<LiveRange*,std::pair<BitVector,BitVector>> EntryInfoMap;
+  typedef DenseMap<LiveRange*,std::pair<BitVector,BitVector>> EntryInfoMap;
+  EntryInfoMap EntryInfos;
 
   /// Map each basic block where a live range is live out to the live-out value
   /// and its defining block.