MIPS: NaNs in the snapshot should be quiet according

to the MIPS FPU even when cross-building the snapshot.
This is based on code from Daniel Kalmar from
http://codereview.chromium.org/9910029/
Review URL: https://chromiumcodereview.appspot.com/10068006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11283 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/assembler.h

@@ -62,6 +62,10 @@ class AssemblerBase: public Malloced {
   Isolate* isolate() const { return isolate_; }
   int jit_cookie() { return jit_cookie_; }
 
+  // Overwrite a host NaN with a quiet target NaN.  Used by mksnapshot for
+  // cross-snapshotting.
+  static void QuietNaN(HeapObject* nan) { }
+
  private:
   Isolate* isolate_;
   int jit_cookie_;

src/mips/assembler-mips.cc

@@ -2137,6 +2137,22 @@ Address Assembler::target_address_at(Address pc) {
 }
 
 
+#define MIPS_QNAN_HI 0x7ff7ffff
+#define MIPS_QNAN_LO 0xffffffff
+
+
+void Assembler::QuietNaN(HeapObject* object) {
+  // Mips has a different encoding of qNaN than ia32, so any heap NaN built
+  // with simulator must be re-encoded for the snapshot. Performance hit not
+  // critical at mksnapshot/build time.  We can't use set_value because that
+  // will put the NaN in an fp register, which changes the bits.
+  uint64_t mips_qnan_bits =
+      (static_cast<uint64_t>(MIPS_QNAN_HI) << 32) | MIPS_QNAN_LO;
+  Address value_ptr = object->address() + HeapNumber::kValueOffset;
+  memcpy(value_ptr, &mips_qnan_bits, sizeof(mips_qnan_bits));
+}
+
+
 // On Mips, a target address is stored in a lui/ori instruction pair, each
 // of which load 16 bits of the 32-bit address to a register.
 // Patching the address must replace both instr, and flush the i-cache.

src/mips/assembler-mips.h

@@ -570,6 +570,8 @@ class Assembler : public AssemblerBase {
 
   static void JumpLabelToJumpRegister(Address pc);
 
+  static void QuietNaN(HeapObject* nan);
+
   // This sets the branch destination (which gets loaded at the call address).
   // This is for calls and branches within generated code.  The serializer
   // has already deserialized the lui/ori instructions etc.

src/serialize.cc

@@ -1444,6 +1444,8 @@ void Serializer::ObjectSerializer::Serialize() {
     sink_->PutSection(space, "NewPageSpace");
   }
 
+  if (object_->IsNaN()) Assembler::QuietNaN(object_);
+
   // Serialize the map (first word of the object).
   serializer_->SerializeObject(object_->map(), kPlain, kStartOfObject);