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 9673f80e0856678b2f14d9ab4bdcf8ed351614d9..47ba1ff0454289181c1ddfb45bc10bc466715c32 100644 (file)
--- a/include/llvm/CodeGen/LiveIntervalAnalysis.h
+++ b/include/llvm/CodeGen/LiveIntervalAnalysis.h
@@ -147,13 +147,12 @@ extern cl::opt<bool> UseSegmentSetForPhysRegs;
     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);
 
@@ -161,6 +160,8 @@ extern cl::opt<bool> UseSegmentSetForPhysRegs;
     /// 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