Subzero: Improve usability of liveness-related tools.

src/IceInst.h

 //===- subzero/src/IceInst.h - High-level instructions ----------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 74 matching lines @@
     NumberExtended = NumberInitial - 1
   };
 
   bool isDeleted() const { return Deleted; }
   void setDeleted() { Deleted = true; }
   void setDead(bool Value = true) { Dead = Value; }
   void deleteIfDead();
 
   bool hasSideEffects() const { return HasSideEffects; }
 
-  bool isDestNonKillable() const { return IsDestNonKillable; }
-  void setDestNonKillable() { IsDestNonKillable = true; }
+  bool isDestRedefined() const { return IsDestRedefined; }
+  void setDestRedefined() { IsDestRedefined = true; }
 
   Variable *getDest() const { return Dest; }
 
   SizeT getSrcSize() const { return NumSrcs; }
   Operand *getSrc(SizeT I) const {
     assert(I < getSrcSize());
     return Srcs[I];
   }
 
   bool isLastUse(const Operand *Src) const;
@@ skipping 78 matching lines @@
   /// Deleted means irrevocably deleted.
   bool Deleted = false;
   /// Dead means one of two things depending on context: (1) pending deletion
   /// after liveness analysis converges, or (2) marked for deletion during
   /// lowering due to a folded bool operation.
   bool Dead = false;
   /// HasSideEffects means the instruction is something like a function call or
   /// a volatile load that can't be removed even if its Dest variable is not
   /// live.
   bool HasSideEffects = false;
-  /// IsDestNonKillable means that liveness analysis shouldn't consider this
-  /// instruction to kill the Dest variable. This is used when lowering produces
-  /// two assignments to the same variable.
-  bool IsDestNonKillable = false;
+  /// IsDestRedefined indicates that this instruction is not the first
+  /// definition of Dest in the basic block.  The effect is that liveness
+  /// analysis shouldn't consider this instruction to be the start of Dest's
+  /// live range; rather, there is some other instruction earlier in the basic
+  /// block with the same Dest.  This is maintained because liveness analysis
+  /// has an invariant (primarily for performance reasons) that any Variable's
+  /// live range recorded in a basic block has at most one start and at most one
+  /// end.
+  bool IsDestRedefined = false;
 
   Variable *Dest;
   const SizeT MaxSrcs; // only used for assert
   SizeT NumSrcs = 0;
   Operand **Srcs;
 
   /// LiveRangesEnded marks which Variables' live ranges end in this
   /// instruction. An instruction can have an arbitrary number of source
   /// operands (e.g. a call instruction), and each source operand can contain 0
   /// or 1 Variable (and target-specific operands could contain more than 1
@@ skipping 763 matching lines @@
   static void noteHead(Ice::Inst *, Ice::Inst *) {}
   void deleteNode(Ice::Inst *) {}
 
 private:
   mutable ilist_half_node<Ice::Inst> Sentinel;
 };
 
 } // end of namespace llvm
 
 #endif // SUBZERO_SRC_ICEINST_H