Subzero: Allow deeper levels of variable splitting.

src/IceInst.cpp

 //===- subzero/src/IceInst.cpp - High-level instruction implementation ----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 1076 matching lines @@
 
 bool checkForRedundantAssign(const Variable *Dest, const Operand *Source) {
   const auto *SrcVar = llvm::dyn_cast<const Variable>(Source);
   if (!SrcVar)
     return false;
   if (Dest->hasReg() && Dest->getRegNum() == SrcVar->getRegNum()) {
     // TODO: On x86-64, instructions like "mov eax, eax" are used to clear the
     // upper 32 bits of rax. We need to recognize and preserve these.
     return true;
   }
-  if (!Dest->hasReg() && !SrcVar->hasReg() &&
-      Dest->getStackOffset() == SrcVar->getStackOffset())
+  if (!Dest->hasReg() && !SrcVar->hasReg()) {
+    if (!Dest->hasStackOffset() || !SrcVar->hasStackOffset()) {
+      return false;
+    }
+    if (Dest->getStackOffset() != SrcVar->getStackOffset()) {
+      return false;
+    }
     return true;
+  }
   return false;
 }
 
 } // end of namespace Ice