Subzero: Improve the representation and handling of the FakeKill instruction.

src/IceOperand.cpp

 //===- subzero/src/IceOperand.cpp - High-level operand implementation -----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the Operand class and its target-independent
@@ skipping 332 matching lines @@
         const bool IsFromDef = false;
         const bool IsImplicit = false;
         Metadata[VarNum].markUse(Kind, I, Node, IsFromDef, IsImplicit);
       }
     }
   }
 
   for (Inst *I : Node->getInsts()) {
     if (I->isDeleted())
       continue;
-    if (InstFakeKill *Kill = llvm::dyn_cast<InstFakeKill>(I)) {
-      // A FakeKill instruction indicates certain Variables (usually
-      // physical scratch registers) are redefined, so we register
-      // them as defs.
-      for (SizeT SrcNum = 0; SrcNum < I->getSrcSize(); ++SrcNum) {
-        Variable *Var = llvm::cast<Variable>(I->getSrc(SrcNum));
-        SizeT VarNum = Var->getIndex();
-        assert(VarNum < Metadata.size());
-        Metadata[VarNum].markDef(Kind, Kill, Node);
-      }
-      continue; // no point in executing the rest
-    }
+    // Note: The implicit definitions (and uses) from InstFakeKill are
+    // deliberately ignored.
     if (Variable *Dest = I->getDest()) {
       SizeT DestNum = Dest->getIndex();
       assert(DestNum < Metadata.size());
       Metadata[DestNum].markDef(Kind, I, Node);
     }
     for (SizeT SrcNum = 0; SrcNum < I->getSrcSize(); ++SrcNum) {
       Operand *Src = I->getSrc(SrcNum);
       SizeT NumVars = Src->getNumVars();
       for (SizeT J = 0; J < NumVars; ++J) {
         const Variable *Var = Src->getVar(J);
@@ skipping 143 matching lines @@
 
 Ostream &operator<<(Ostream &Str, const RegWeight &W) {
   if (W.getWeight() == RegWeight::Inf)
     Str << "Inf";
   else
     Str << W.getWeight();
   return Str;
 }
 
 } // end of namespace Ice