Fix leaf floating point runtime calls on ARM (work still needed in simulator).

runtime/vm/simulator_arm.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 <math.h>  // for isnan.
 #include <setjmp.h>
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM)
@@ skipping 1476 matching lines @@
         }
         set_top_exit_frame_info(0);
 
         // Zap caller-saved registers, since the actual runtime call could have
         // used them.
         set_register(R1, icount_);
         set_register(R2, icount_);
         set_register(R3, icount_);
         set_register(IP, icount_);
         set_register(LR, icount_);
-        float zap_fvalue = static_cast<float>(icount_);
-        for (int i = S0; i <= S15; i++) {
-          set_sregister(static_cast<SRegister>(i), zap_fvalue);
+        double zap_dvalue = static_cast<double>(icount_);
+        for (int i = D0; i <= D7; i++) {
+          set_dregister(static_cast<DRegister>(i), zap_dvalue);
         }
+        // The above loop also zaps overlapping registers S0-S15.
+        // Registers D8-D15 (overlapping with S16-S31) are preserved.
 #ifdef VFPv3_D32
-        double zap_dvalue = static_cast<double>(icount_);
         for (int i = D16; i <= D31; i++) {
           set_dregister(static_cast<DRegister>(i), zap_dvalue);
         }
 #endif  // VFPv3_D32
 
         // Return.
         set_pc(saved_lr);
       } else {
         // Coming via long jump from a throw. Continue to exception handler.
         set_top_exit_frame_info(0);
@@ skipping 1535 matching lines @@
     set_register(kStackTraceObjectReg, bit_cast<int32_t>(raw_stacktrace));
   }
   buf->Longjmp();
 }
 
 }  // namespace dart
 
 #endif  // !defined(HOST_ARCH_ARM)
 
 #endif  // defined TARGET_ARCH_ARM