Fix -Wstrict-aliasing warnings.

src/hydrogen.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 3576 matching lines @@
 static bool BoundsCheckKeyMatch(void* key1, void* key2) {
   BoundsCheckKey* k1 = static_cast<BoundsCheckKey*>(key1);
   BoundsCheckKey* k2 = static_cast<BoundsCheckKey*>(key2);
   return k1->IndexBase() == k2->IndexBase() && k1->Length() == k2->Length();
 }
 
 
 class BoundsCheckTable : private ZoneHashMap {
  public:
   BoundsCheckBbData** LookupOrInsert(BoundsCheckKey* key, Zone* zone) {
-    return reinterpret_cast<BoundsCheckBbData**>(
-        &(Lookup(key, key->Hash(), true, ZoneAllocationPolicy(zone))->value));
+    // Avoid type-punning compiler warnings.
+    union {
+      void** in;
+      BoundsCheckBbData** out;
+    } u;
+    u.in = &(Lookup(key, key->Hash(), true, ZoneAllocationPolicy(zone))->value);
+    return u.out;
   }
 
   void Insert(BoundsCheckKey* key, BoundsCheckBbData* data, Zone* zone) {
     Lookup(key, key->Hash(), true, ZoneAllocationPolicy(zone))->value = data;
   }
 
   void Delete(BoundsCheckKey* key) {
     Remove(key, key->Hash());
   }
 
@@ skipping 6507 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal