Cache current thread in a reserved register and use it in LoadIsolate

runtime/vm/flow_graph_allocator.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/flow_graph_allocator.h"
 
 #include "vm/bit_vector.h"
 #include "vm/intermediate_language.h"
 #include "vm/il_printer.h"
 #include "vm/flow_graph.h"
@@ skipping 100 matching lines @@
     blocked_cpu_registers_[TMP] = true;
   }
   if (TMP2 != kNoRegister) {
     blocked_cpu_registers_[TMP2] = true;
   }
   if (PP != kNoRegister) {
     blocked_cpu_registers_[PP] = true;
   }
   blocked_cpu_registers_[SPREG] = true;
   blocked_cpu_registers_[FPREG] = true;
+  blocked_cpu_registers_[THR] = true;
 
   // FpuTMP is used as scratch by optimized code and parallel move resolver.
   blocked_fpu_registers_[FpuTMP] = true;
 
   // Block additional registers needed preserved when generating intrinsics.
   // TODO(fschneider): Handle saving and restoring these registers when
   // generating intrinsic code.
   if (intrinsic_mode) {
     blocked_cpu_registers_[ARGS_DESC_REG] = true;
   }
@@ skipping 2839 matching lines @@
     ISL_Print("-- [after ssa allocator] ir [%s] -------------\n",
               function.ToFullyQualifiedCString());
     FlowGraphPrinter printer(flow_graph_, true);
     printer.PrintBlocks();
     ISL_Print("----------------------------------------------\n");
   }
 }
 
 
 }  // namespace dart