Subzero: Simplify the FakeKill instruction.

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.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares the Inst class and its target-independent
@@ skipping 764 matching lines @@
   void emit(const Cfg *Func) const override;
   void emitIAS(const Cfg * /* Func */) const override {}
   void dump(const Cfg *Func) const override;
   static bool classof(const Inst *Inst) { return Inst->getKind() == FakeUse; }
 
 private:
   InstFakeUse(Cfg *Func, Variable *Src);
   ~InstFakeUse() override {}
 };
 
-// FakeKill instruction.  This "kills" a set of variables by adding a
-// trivial live range at this instruction to each variable.  The
-// primary use is to indicate that scratch registers are killed after
-// a call, so that the register allocator won't assign a scratch
-// register to a variable whose live range spans a call.
+// FakeKill instruction.  This "kills" a set of variables by modeling
+// a trivial live range at this instruction for each (implicit)
+// variable.  The primary use is to indicate that scratch registers
+// are killed after a call, so that the register allocator won't
+// assign a scratch register to a variable whose live range spans a
+// call.
 //
 // The FakeKill instruction also holds a pointer to the instruction
 // that kills the set of variables, so that if that linked instruction
 // gets dead-code eliminated, the FakeKill instruction will as well.
 class InstFakeKill : public InstHighLevel {
   InstFakeKill(const InstFakeKill &) = delete;
   InstFakeKill &operator=(const InstFakeKill &) = delete;
 
 public:
-  static InstFakeKill *create(Cfg *Func, const VarList &KilledRegs,
-                              const Inst *Linked) {
-    return new (Func->allocateInst<InstFakeKill>())
-        InstFakeKill(Func, KilledRegs, Linked);
+  static InstFakeKill *create(Cfg *Func, const Inst *Linked) {
+    return new (Func->allocateInst<InstFakeKill>()) InstFakeKill(Func, Linked);
   }
-  const VarList &getKilledRegs() const { return KilledRegs; }
   const Inst *getLinked() const { return Linked; }
   void emit(const Cfg *Func) const override;
   void emitIAS(const Cfg * /* Func */) const override {}
   void dump(const Cfg *Func) const override;
   static bool classof(const Inst *Inst) { return Inst->getKind() == FakeKill; }
 
 private:
-  InstFakeKill(Cfg *Func, const VarList &KilledRegs, const Inst *Linked);
+  InstFakeKill(Cfg *Func, const Inst *Linked);
   ~InstFakeKill() override {}
 
-  const VarList &KilledRegs;
   // This instruction is ignored if Linked->isDeleted() is true.
   const Inst *Linked;
 };
 
 // The Target instruction is the base class for all target-specific
 // instructions.
 class InstTarget : public Inst {
   InstTarget(const InstTarget &) = delete;
   InstTarget &operator=(const InstTarget &) = delete;
 
@@ skipping 24 matching lines @@
   Ice::Inst *provideInitialHead() const { return createSentinel(); }
   Ice::Inst *ensureHead(Ice::Inst *) const { return createSentinel(); }
   static void noteHead(Ice::Inst *, Ice::Inst *) {}
   void deleteNode(Ice::Inst *) {}
 
 private:
   mutable ilist_half_node<Ice::Inst> Sentinel;
 };
 
 #endif // SUBZERO_SRC_ICEINST_H