Subzero: Fix address mode optimization involving phi temporaries.

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 128 matching lines @@
 }
 
 void Variable::setUse(const Inst *Inst, const CfgNode *Node) {
   if (DefNode == NULL)
     return;
   if (llvm::isa<InstPhi>(Inst) || Node != DefNode)
     DefNode = NULL;
 }
 
 void Variable::setDefinition(Inst *Inst, const CfgNode *Node) {
+  if (DefInst && !DefInst->isDeleted() && DefInst != Inst) {
+    // Detect when a variable is being defined multiple times,
+    // particularly for Phi instruction lowering.  If this happens, we
+    // need to lock DefInst to NULL.
+    DefInst = NULL;
+    DefNode = NULL;
+    return;
+  }
   if (DefNode == NULL)
     return;
-  // Can first check preexisting DefInst if we care about multi-def vars.
   DefInst = Inst;
   if (Node != DefNode)
     DefNode = NULL;
 }
 
 void Variable::replaceDefinition(Inst *Inst, const CfgNode *Node) {
   DefInst = NULL;
   setDefinition(Inst, Node);
 }
 
@@ skipping 96 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