Subzero: Fix inappropriate use of nullptr.

src/IceTargetLoweringX8632.cpp

 //===- subzero/src/IceTargetLoweringX8632.cpp - x86-32 lowering -----------===//
 //
 //                        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 TargetLoweringX8632 class, which
@@ skipping 3432 matching lines @@
         Variable *ValLo = llvm::cast<Variable>(loOperand(ValVar));
         Variable *ValHi = llvm::cast<Variable>(hiOperand(ValVar));
         Context.insert(InstFakeUse::create(Func, ValLo));
         Context.insert(InstFakeUse::create(Func, ValHi));
       }
     } else {
       // For xchg, the loop is slightly smaller and ebx/ecx are used.
       Context.insert(InstFakeUse::create(Func, T_ebx));
       Context.insert(InstFakeUse::create(Func, T_ecx));
     }
-    // The address base is also reused in the loop.
-    Context.insert(InstFakeUse::create(Func, Addr->getBase()));
+    // The address base (if any) is also reused in the loop.
+    if (Variable *Base = Addr->getBase())
+      Context.insert(InstFakeUse::create(Func, Base));
     Variable *DestLo = llvm::cast<Variable>(loOperand(Dest));
     Variable *DestHi = llvm::cast<Variable>(hiOperand(Dest));
     _mov(DestLo, T_eax);
     _mov(DestHi, T_edx);
     return;
   }
   OperandX8632Mem *Addr = FormMemoryOperand(Ptr, Ty);
   Variable *T_eax = makeReg(Ty, RegX8632::Reg_eax);
   _mov(T_eax, Addr);
   InstX8632Label *Label = InstX8632Label::create(Func, this);
   Context.insert(Label);
   // We want to pick a different register for T than Eax, so don't use
   // _mov(T == nullptr, T_eax).
   Variable *T = makeReg(Ty);
   _mov(T, T_eax);
   (this->*Op_Lo)(T, Val);
   const bool Locked = true;
   _cmpxchg(Addr, T_eax, T, Locked);
   _br(CondX86::Br_ne, Label);
   // If Val is a variable, model the extended live range of Val through
   // the end of the loop, since it will be re-used by the loop.
   if (Variable *ValVar = llvm::dyn_cast<Variable>(Val)) {
     Context.insert(InstFakeUse::create(Func, ValVar));
   }
-  // The address base is also reused in the loop.
-  Context.insert(InstFakeUse::create(Func, Addr->getBase()));
+  // The address base (if any) is also reused in the loop.
+  if (Variable *Base = Addr->getBase())
+    Context.insert(InstFakeUse::create(Func, Base));
   _mov(Dest, T_eax);
 }
 
 // Lowers count {trailing, leading} zeros intrinsic.
 //
 // We could do constant folding here, but that should have
 // been done by the front-end/middle-end optimizations.
 void TargetX8632::lowerCountZeros(bool Cttz, Type Ty, Variable *Dest,
                                   Operand *FirstVal, Operand *SecondVal) {
   // TODO(jvoung): Determine if the user CPU supports LZCNT (BMI).
@@ skipping 1356 matching lines @@
   case FT_Asm:
   case FT_Iasm: {
     OstreamLocker L(Ctx);
     emitConstantPool<PoolTypeConverter<float>>(Ctx);
     emitConstantPool<PoolTypeConverter<double>>(Ctx);
   } break;
   }
 }
 
 } // end of namespace Ice