Let NaN flow as double into HBranch

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index 1dac13d2b8f979fb30251032ccc0f91864c7d90c..296458f3ef2d56d23a7edf452d9be6da40677881 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -1919,10 +1919,22 @@ void LCodeGen::DoBranch(LBranch* instr) {
       ASSERT(!info()->IsStub());
       __ SmiCompare(reg, Smi::FromInt(0));
       EmitBranch(instr, not_equal);
+    } else if (type.IsJSArray()) {
+      ASSERT(!info()->IsStub());
+      EmitBranch(instr, no_condition);
+    } else if (type.IsHeapNumber()) {
+      ASSERT(!info()->IsStub());
+      __ xorps(xmm0, xmm0);
+      __ ucomisd(xmm0, FieldOperand(reg, HeapNumber::kValueOffset));
+      EmitBranch(instr, not_equal);
+    } else if (type.IsString()) {
+      ASSERT(!info()->IsStub());
+      __ cmpq(FieldOperand(reg, String::kLengthOffset), Immediate(0));
+      EmitBranch(instr, not_equal);
     } else {
       ToBooleanStub::Types expected = instr->hydrogen()->expected_input_types();
       // Avoid deopts in the case where we've never executed this path before.
-      if (expected.IsEmpty()) expected = ToBooleanStub::all_types();
+      if (expected.IsEmpty()) expected = ToBooleanStub::Types::Generic();
 
       if (expected.Contains(ToBooleanStub::UNDEFINED)) {
         // undefined -> false.
@@ -1995,8 +2007,11 @@ void LCodeGen::DoBranch(LBranch* instr) {
         __ bind(&not_heap_number);
       }
 
-      // We've seen something for the first time -> deopt.
-      DeoptimizeIf(no_condition, instr->environment());
+      if (!expected.IsGeneric()) {
+        // We've seen something for the first time -> deopt.
+        // This can only happen if we are not generic already.
+        DeoptimizeIf(no_condition, instr->environment());
+      }
     }
   }
 }