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

runtime/vm/flow_graph_compiler_mips.cc

 // Copyright (c) 2013, 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_MIPS.
 #if defined(TARGET_ARCH_MIPS)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/ast_printer.h"
@@ skipping 1257 matching lines @@
   ASSERT(Array::Handle(ic_data.arguments_descriptor()).Length() > 0);
   __ Comment("InstanceCall");
   __ LoadObject(S5, ic_data);
   GenerateDartCall(deopt_id,
                    token_pos,
                    target_label,
                    RawPcDescriptors::kIcCall,
                    locs);
   __ Comment("InstanceCall return");
   __ Drop(argument_count);
-#if defined(DEBUG)
-  __ LoadImmediate(S4, kInvalidObjectPointer);
-#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 63 matching lines @@
   StubCode* stub_code = isolate()->stub_code();
   const uword label_address =
       stub_code->UnoptimizedStaticCallEntryPoint(ic_data.NumArgsTested());
   ExternalLabel target_label(label_address);
   __ LoadObject(S5, ic_data);
   GenerateDartCall(deopt_id,
                    token_pos,
                    &target_label,
                    RawPcDescriptors::kUnoptStaticCall,
                    locs);
-#if defined(DEBUG)
-  __ LoadImmediate(S4, kInvalidObjectPointer);
-  __ LoadImmediate(S5, kInvalidObjectPointer);
-#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 68 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(S4, kInvalidObjectPointer);
-      __ LoadImmediate(S5, kInvalidObjectPointer);
-    }
-#endif
     __ Comment("EqualityRegRegCompare return");
     // Stub returns result in CMPRES1 (if it is 0, then left and right are
     // equal).
     __ lw(right, Address(SP, 0 * kWordSize));
     __ lw(left, Address(SP, 1 * kWordSize));
     __ addiu(SP, SP, Immediate(2 * kWordSize));
     return Condition(CMPRES1, ZR, EQ);
   } else {
     return Condition(left, right, EQ);
   }
@@ skipping 387 matching lines @@
   __ AddImmediate(SP, kDoubleSize);
 }
 
 
 #undef __
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS