MIPS: Do the qNaN fixup at de-serialization time. This is a commit of...

MIPS: Do the qNaN fixup at de-serialization time.  This is a commit of https://chromiumcodereview.appspot.com/10093007/ for Paul Lind

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11405 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/isolate.cc

@@ -1842,6 +1842,9 @@ bool Isolate::Init(Deserializer* des) {
   // stack guard.
   heap_.SetStackLimits();
 
+  // Quiet the heap NaN if needed on target platform.
+  if (des != NULL) Assembler::QuietNaN(heap_.nan_value());
+
   deoptimizer_data_ = new DeoptimizerData;
   runtime_profiler_ = new RuntimeProfiler(this);
   runtime_profiler_->SetUp();

src/mips/assembler-mips.cc

@@ -2137,19 +2137,12 @@ Address Assembler::target_address_at(Address pc) {
 }
 
 
-#define MIPS_QNAN_HI 0x7ff7ffff
-#define MIPS_QNAN_LO 0xffffffff
-
-
+// MIPS and ia32 use opposite encoding for qNaN and sNaN, such that ia32
+// qNaN is a MIPS sNaN, and ia32 sNaN is MIPS qNaN. If running from a heap
+// snapshot generated on ia32, the resulting MIPS sNaN must be quieted.
+// OS::nan_value() returns a qNaN.
 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));
+  HeapNumber::cast(object)->set_value(OS::nan_value());
 }
 
 

src/runtime.cc

@@ -8432,6 +8432,12 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_CheckIsBootstrapping) {
 }
 
 
+RUNTIME_FUNCTION(MaybeObject*, Runtime_GetRootNaN) {
+  RUNTIME_ASSERT(isolate->bootstrapper()->IsActive());
+  return isolate->heap()->nan_value();
+}
+
+
 RUNTIME_FUNCTION(MaybeObject*, Runtime_Call) {
   HandleScope scope(isolate);
   ASSERT(args.length() >= 2);

src/runtime.h

@@ -77,6 +77,7 @@ namespace internal {
   \
   /* Utilities */ \
   F(CheckIsBootstrapping, 0, 1) \
+  F(GetRootNaN, 0, 1) \
   F(Call, -1 /* >= 2 */, 1) \
   F(Apply, 5, 1) \
   F(GetFunctionDelegate, 1, 1) \

src/runtime.js

@@ -47,7 +47,7 @@ var $String = global.String;
 var $Number = global.Number;
 var $Function = global.Function;
 var $Boolean = global.Boolean;
-var $NaN = 0/0;
+var $NaN = %GetRootNaN();
 var builtins = this;
 
 // ECMA-262 Section 11.9.3.

src/serialize.cc

@@ -1444,8 +1444,6 @@ 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);