Lazily defer duplicating the live interval we are splitting until we know it is

necessary.

Sometimes, live range splitting doesn't shrink the current interval, but simply
changes some instructions to use a new interval. That makes the original more
suitable for spilling. In this case, we don't need to duplicate the original.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110481 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 14 deletions

diff --git a/lib/CodeGen/SplitKit.h b/lib/CodeGen/SplitKit.h
index 6ded4f464c..d5136877de 100644
--- a/lib/CodeGen/SplitKit.h
+++ b/lib/CodeGen/SplitKit.h
@@ -121,8 +121,7 @@ public:
 /// SplitEditor - Edit machine code and LiveIntervals for live range
 /// splitting.
 ///
-/// - Create a SplitEditor from a SplitAnalysis. This will create a new
-///   LiveInterval, dupli, that is identical to SA.curli.
+/// - Create a SplitEditor from a SplitAnalysis.
 /// - Start a new live interval with openIntv.
 /// - Mark the places where the new interval is entered using enterIntv*
 /// - Mark the ranges where the new interval is used with useIntv* 
@@ -137,8 +136,12 @@ class SplitEditor {
   MachineRegisterInfo &mri_;
   const TargetInstrInfo &tii_;
 
-  /// dupli_ - Created as a copy of sa_.curli_, ranges are carved out as new
-  /// intervals get added through openIntv / closeIntv.
+  /// curli_ - The immutable interval we are currently splitting.
+  const LiveInterval *const curli_;
+
+  /// dupli_ - Created as a copy of curli_, ranges are carved out as new
+  /// intervals get added through openIntv / closeIntv. This is used to avoid
+  /// editing curli_.
   LiveInterval *dupli_;
 
   /// Currently open LiveInterval.
@@ -148,13 +151,16 @@ class SplitEditor {
   /// register class and spill slot as curli.
   LiveInterval *createInterval();
 
-	/// valueMap_ - Map values in dupli to values in openIntv. These are direct 1-1
-	/// mappings, and do not include values created by inserted copies.
-	DenseMap<VNInfo*,VNInfo*> valueMap_;
+  /// getDupLI - Ensure dupli is created and return it.
+  LiveInterval *getDupLI();
+
+  /// valueMap_ - Map values in dupli to values in openIntv. These are direct 1-1
+  /// mappings, and do not include values created by inserted copies.
+  DenseMap<const VNInfo*, VNInfo*> valueMap_;
 
-	/// mapValue - Return the openIntv value that corresponds to the given dupli
-	/// value.
-	VNInfo *mapValue(VNInfo *dupliVNI);
+  /// mapValue - Return the openIntv value that corresponds to the given curli
+  /// value.
+  VNInfo *mapValue(const VNInfo *curliVNI);
 
   /// A dupli value is live through openIntv.
   bool liveThrough_;
@@ -178,8 +184,8 @@ public:
   SplitEditor(SplitAnalysis &SA, LiveIntervals&, VirtRegMap&,
               std::vector<LiveInterval*> &newIntervals);
 
-	/// getAnalysis - Get the corresponding analysis.
-	SplitAnalysis &getAnalysis() { return sa_; }
+  /// getAnalysis - Get the corresponding analysis.
+  SplitAnalysis &getAnalysis() { return sa_; }
 
   /// Create a new virtual register and live interval.
   void openIntv();
@@ -210,8 +216,9 @@ public:
   // ===--- High level methods ---===
 
   /// splitAroundLoop - Split curli into a separate live interval inside
-  /// the loop.
-  void splitAroundLoop(const MachineLoop*);
+  /// the loop. Return true if curli has been completely replaced, false if
+  /// curli is still intact, and needs to be spilled or split further.
+  bool splitAroundLoop(const MachineLoop*);
 
 };