LiveInterval: Document and enforce rules about empty subranges.

[oota-llvm.git] / include / llvm / CodeGen / LiveIntervalAnalysis.h

diff --git a/include/llvm/CodeGen/LiveIntervalAnalysis.h b/include/llvm/CodeGen/LiveIntervalAnalysis.h
index d97087036976520a433666430e669a85e9ce0419..47ba1ff0454289181c1ddfb45bc10bc466715c32 100644 (file)
--- a/include/llvm/CodeGen/LiveIntervalAnalysis.h
+++ b/include/llvm/CodeGen/LiveIntervalAnalysis.h
@@ -27,12 +27,15 @@
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/SlotIndexes.h"
 #include "llvm/Support/Allocator.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 #include <cmath>
 #include <iterator>
 
 namespace llvm {
 
+extern cl::opt<bool> UseSegmentSetForPhysRegs;
+
   class AliasAnalysis;
   class BitVector;
   class BlockFrequency;
@@ -97,7 +100,7 @@ namespace llvm {
   public:
     static char ID; // Pass identification, replacement for typeid
     LiveIntervals();
-    virtual ~LiveIntervals();
+    ~LiveIntervals() override;
 
     // Calculate the spill weight to assign to a single instruction.
     static float getSpillWeight(bool isDef, bool isUse,
@@ -144,13 +147,12 @@ namespace llvm {
     LiveInterval::Segment addSegmentToEndOfBlock(unsigned reg,
                                                  MachineInstr* startInst);
 
-    /// shrinkToUses - After removing some uses of a register, shrink its live
-    /// range to just the remaining uses. This method does not compute reaching
-    /// defs for new uses, and it doesn't remove dead defs.
-    /// Dead PHIDef values are marked as unused.
-    /// New dead machine instructions are added to the dead vector.
-    /// Return true if the interval may have been separated into multiple
-    /// connected components.
+    /// After removing some uses of a register, shrink its live range to just
+    /// the remaining uses. This method does not compute reaching defs for new
+    /// uses, and it doesn't remove dead defs.
+    /// Dead PHIDef values are marked as unused. New dead machine instructions
+    /// are added to the dead vector. Returns true if the interval may have been
+    /// separated into multiple connected components.
     bool shrinkToUses(LiveInterval *li,
                       SmallVectorImpl<MachineInstr*> *dead = nullptr);
 
@@ -158,6 +160,8 @@ namespace llvm {
     /// shrinkToUses(LiveInterval *li, SmallVectorImpl<MachineInstr*> *dead)
     /// that works on a subregister live range and only looks at uses matching
     /// the lane mask of the subregister range.
+    /// This may leave the subrange empty which needs to be cleaned up with
+    /// LiveInterval::removeEmptySubranges() afterwards.
     void shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg);
 
     /// extendToIndices - Extend the live range of LI to reach all points in
@@ -377,7 +381,8 @@ namespace llvm {
       LiveRange *LR = RegUnitRanges[Unit];
       if (!LR) {
         // Compute missing ranges on demand.
-        RegUnitRanges[Unit] = LR = new LiveRange();
+        // Use segment set to speed-up initial computation of the live range.
+        RegUnitRanges[Unit] = LR = new LiveRange(UseSegmentSetForPhysRegs);
         computeRegUnitRange(*LR, Unit);
       }
       return *LR;
@@ -393,8 +398,15 @@ namespace llvm {
       return RegUnitRanges[Unit];
     }
 
+    /// Remove value numbers and related live segments starting at position
+    /// @p Pos that are part of any liverange of physical register @p Reg or one
+    /// of its subregisters.
     void removePhysRegDefAt(unsigned Reg, SlotIndex Pos);
 
+    /// Remove value number and related live segments of @p LI and its subranges
+    /// that start at position @p Pos.
+    void removeVRegDefAt(LiveInterval &LI, SlotIndex Pos);
+
   private:
     /// Compute live intervals for all virtual registers.
     void computeVirtRegs();