[turbofan] Build s/NULL/nullptr/g and CHECK(x != nullptr) to CHECK_NOT_NULL(x).

src/compiler/ppc/code-generator-ppc.cc

Index: src/compiler/ppc/code-generator-ppc.cc
diff --git a/src/compiler/ppc/code-generator-ppc.cc b/src/compiler/ppc/code-generator-ppc.cc
index e1a7be2b3cc44a943d07a10ccd3682a1d849e6f3..8ceb159534d8ca56c6c2cdb847a65dd6f1a9c983 100644
--- a/src/compiler/ppc/code-generator-ppc.cc
+++ b/src/compiler/ppc/code-generator-ppc.cc
@@ -101,7 +101,7 @@ class PPCOperandConverter final : public InstructionOperandConverter {
   }
 
   MemOperand ToMemOperand(InstructionOperand* op) const {
-    DCHECK(op != NULL);
+    DCHECK_NOT_NULL(op);
     DCHECK(op->IsStackSlot() || op->IsDoubleStackSlot());
     FrameOffset offset = frame_access_state()->GetFrameOffset(
         AllocatedOperand::cast(op)->index());
@@ -1640,7 +1640,7 @@ void CodeGenerator::AssembleReturn() {
 
 void CodeGenerator::AssembleMove(InstructionOperand* source,
                                  InstructionOperand* destination) {
-  PPCOperandConverter g(this, NULL);
+  PPCOperandConverter g(this, nullptr);
   // Dispatch on the source and destination operand kinds.  Not all
   // combinations are possible.
   if (source->IsRegister()) {
@@ -1742,7 +1742,7 @@ void CodeGenerator::AssembleMove(InstructionOperand* source,
 
 void CodeGenerator::AssembleSwap(InstructionOperand* source,
                                  InstructionOperand* destination) {
-  PPCOperandConverter g(this, NULL);
+  PPCOperandConverter g(this, nullptr);
   // Dispatch on the source and destination operand kinds.  Not all
   // combinations are possible.
   if (source->IsRegister()) {