Remove zapping of registers that has not turned up any GC bugs in a long time.

runtime/vm/flow_graph_compiler_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_ARM64.
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/ast_printer.h"
@@ skipping 1235 matching lines @@
                                          intptr_t token_pos,
                                          LocationSummary* locs) {
   ASSERT(Array::Handle(ic_data.arguments_descriptor()).Length() > 0);
   __ LoadObject(R5, ic_data, PP);
   GenerateDartCall(deopt_id,
                    token_pos,
                    target_label,
                    RawPcDescriptors::kIcCall,
                    locs);
   __ Drop(argument_count);
-#if defined(DEBUG)
-  __ LoadImmediate(R4, kInvalidObjectPointer, kNoPP);
-#endif
 }
 
 
 void FlowGraphCompiler::EmitMegamorphicInstanceCall(
     const ICData& ic_data,
     intptr_t argument_count,
     intptr_t deopt_id,
     intptr_t token_pos,
     LocationSummary* locs) {
   MegamorphicCacheTable* table = Isolate::Current()->megamorphic_cache_table();
@@ skipping 61 matching lines @@
   StubCode* stub_code = isolate()->stub_code();
   const uword label_address =
       stub_code->UnoptimizedStaticCallEntryPoint(ic_data.NumArgsTested());
   ExternalLabel target_label(label_address);
   __ LoadObject(R5, ic_data, PP);
   GenerateDartCall(deopt_id,
                    token_pos,
                    &target_label,
                    RawPcDescriptors::kUnoptStaticCall,
                    locs);
-#if defined(DEBUG)
-  __ LoadImmediate(R4, kInvalidObjectPointer, kNoPP);
-  __ LoadImmediate(R5, kInvalidObjectPointer, kNoPP);
-#endif
   __ Drop(argument_count);
 }
 
 
 void FlowGraphCompiler::EmitOptimizedStaticCall(
     const Function& function,
     const Array& arguments_descriptor,
     intptr_t argument_count,
     intptr_t deopt_id,
     intptr_t token_pos,
@@ skipping 57 matching lines @@
           &stub_code->OptimizedIdenticalWithNumberCheckLabel());
     } else {
       __ BranchLinkPatchable(
           &stub_code->UnoptimizedIdenticalWithNumberCheckLabel());
     }
     if (token_pos != Scanner::kNoSourcePos) {
       AddCurrentDescriptor(RawPcDescriptors::kRuntimeCall,
                            Isolate::kNoDeoptId,
                            token_pos);
     }
-#if defined(DEBUG)
-    if (!is_optimizing()) {
-      // Do this *after* adding the pc descriptor!
-      __ LoadImmediate(R4, kInvalidObjectPointer, kNoPP);
-      __ LoadImmediate(R5, kInvalidObjectPointer, kNoPP);
-    }
-#endif
     // Stub returns result in flags (result of a cmp, we need Z computed).
     __ Pop(right);
     __ Pop(left);
   } else {
     __ CompareRegisters(left, right);
   }
   return EQ;
 }
 
 
@@ skipping 398 matching lines @@
 void ParallelMoveResolver::RestoreFpuScratch(FpuRegister reg) {
   __ PopDouble(reg);
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64