Unify the handling of comparinsons against null and undefined.

src/arm/lithium-codegen-arm.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1731 matching lines @@
 void LCodeGen::DoCmpConstantEqAndBranch(LCmpConstantEqAndBranch* instr) {
   Register left = ToRegister(instr->InputAt(0));
   int true_block = chunk_->LookupDestination(instr->true_block_id());
   int false_block = chunk_->LookupDestination(instr->false_block_id());
 
   __ cmp(left, Operand(instr->hydrogen()->right()));
   EmitBranch(true_block, false_block, eq);
 }
 
 
-void LCodeGen::DoIsNullAndBranch(LIsNullAndBranch* instr) {
+void LCodeGen::DoIsNilAndBranch(LIsNilAndBranch* instr) {
   Register scratch = scratch0();
   Register reg = ToRegister(instr->InputAt(0));
+  int false_block = chunk_->LookupDestination(instr->false_block_id());
 
-  // TODO(fsc): If the expression is known to be a smi, then it's
-  // definitely not null. Jump to the false block.
+  // If the expression is known to be untagged or a smi, then it's definitely
+  // not null, and it can't be a an undetectable object.
+  if (instr->hydrogen()->representation().IsSpecialization() ||
+      instr->hydrogen()->type().IsSmi()) {
+    EmitGoto(false_block);
+    return;
+  }
 
   int true_block = chunk_->LookupDestination(instr->true_block_id());
-  int false_block = chunk_->LookupDestination(instr->false_block_id());
-
-  __ LoadRoot(ip, Heap::kNullValueRootIndex);
+  Heap::RootListIndex nil_value = instr->nil() == kNullValue ?
+      Heap::kNullValueRootIndex :
+      Heap::kUndefinedValueRootIndex;
+  __ LoadRoot(ip, nil_value);
   __ cmp(reg, ip);
-  if (instr->is_strict()) {
+  if (instr->kind() == kStrictEquality) {
     EmitBranch(true_block, false_block, eq);
   } else {
+    Heap::RootListIndex other_nil_value = instr->nil() == kNullValue ?
+        Heap::kUndefinedValueRootIndex :
+        Heap::kNullValueRootIndex;
     Label* true_label = chunk_->GetAssemblyLabel(true_block);
     Label* false_label = chunk_->GetAssemblyLabel(false_block);
     __ b(eq, true_label);
-    __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
+    __ LoadRoot(ip, other_nil_value);
     __ cmp(reg, ip);
     __ b(eq, true_label);
     __ JumpIfSmi(reg, false_label);
     // Check for undetectable objects by looking in the bit field in
     // the map. The object has already been smi checked.
     __ ldr(scratch, FieldMemOperand(reg, HeapObject::kMapOffset));
     __ ldrb(scratch, FieldMemOperand(scratch, Map::kBitFieldOffset));
     __ tst(scratch, Operand(1 << Map::kIsUndetectable));
     EmitBranch(true_block, false_block, ne);
   }
@@ skipping 2735 matching lines @@
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 
 
 
 #undef __
 
 } }  // namespace v8::internal