MIPS: avoid alignment issues in FillHeapNumberWithRandom.

src/v8.cc

 // Copyright 2012 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 206 matching lines @@
 // Use a union type to avoid type-aliasing optimizations in GCC.
 typedef union {
   double double_value;
   uint64_t uint64_t_value;
 } double_int_union;
 
 
 Object* V8::FillHeapNumberWithRandom(Object* heap_number,
                                      Context* context) {
   uint64_t random_bits = Random(context);
+#ifdef V8_HOST_ARCH_MIPS

[Yang, 2012/03/06 17:38:38]

We have a flag called V8_TARGET_CAN_READ_UNALIGNED in globals.h.  Maybe it's
better to check against this?

[Erik Corry, 2012/03/07 08:25:53]

I agree with this.

+  // Copy the value to a local variable to avoid alignment issues.
+  double_int_union num;
+  double_int_union* r = #
+  memcpy(r, heap_number + HeapNumber::kValueOffset - kHeapObjectTag,
+      sizeof(num));
+#else
   // Make a double* from address (heap_number + sizeof(double)).
   double_int_union* r = reinterpret_cast<double_int_union*>(
       reinterpret_cast<char*>(heap_number) +
       HeapNumber::kValueOffset - kHeapObjectTag);
+#endif
+
   // Convert 32 random bits to 0.(32 random bits) in a double
   // by computing:
   // ( 1.(20 0s)(32 random bits) x 2^20 ) - (1.0 x 2^20)).
   const double binary_million = 1048576.0;
   r->double_value = binary_million;
   r->uint64_t_value |=  random_bits;
   r->double_value -= binary_million;
 
+#ifdef V8_HOST_ARCH_MIPS
+  memcpy(heap_number + HeapNumber::kValueOffset - kHeapObjectTag, r,
+      sizeof(num));
+#endif
+
   return heap_number;
 }
 
 
 void V8::InitializeOncePerProcess() {
   ScopedLock lock(init_once_mutex);
   if (init_once_called) return;
   init_once_called = true;
 
   // Set up the platform OS support.
@@ skipping 15 matching lines @@
   ElementsAccessor::InitializeOncePerProcess();
 
   if (FLAG_stress_compaction) {
     FLAG_force_marking_deque_overflows = true;
     FLAG_gc_global = true;
     FLAG_max_new_space_size = (1 << (kPageSizeBits - 10)) * 2;
   }
 }
 
 } }  // namespace v8::internal