Use signaling NaN for holes in fixed double arrays.

src/arm64/lithium-codegen-arm64.cc

Index: src/arm64/lithium-codegen-arm64.cc
diff --git a/src/arm64/lithium-codegen-arm64.cc b/src/arm64/lithium-codegen-arm64.cc
index 5a27c4afd535a5198b803bdc5d7eb1b29563804d..e354f5e7428c2123b65ed77a65bd4f7922099bd5 100644
--- a/src/arm64/lithium-codegen-arm64.cc
+++ b/src/arm64/lithium-codegen-arm64.cc
@@ -3605,12 +3605,9 @@ void LCodeGen::DoLoadKeyedFixedDouble(LLoadKeyedFixedDouble* instr) {
 
   if (instr->hydrogen()->RequiresHoleCheck()) {
     Register scratch = ToRegister(instr->temp());
-    // Detect the hole NaN by adding one to the integer representation of the
-    // result, and checking for overflow.
-    STATIC_ASSERT(kHoleNanInt64 == 0x7fffffffffffffff);
     __ Ldr(scratch, mem_op);
-    __ Cmn(scratch, 1);
-    DeoptimizeIf(vs, instr, "hole");
+    __ Cmp(scratch, Operand(kHoleNanInt64, RelocInfo::NONE64));
+    DeoptimizeIf(eq, instr, "hole");

[jbramley, 2015/01/20 14:57:22]

Untested suggestion:

__ Ldr(scratch, mem_op);
__ Eor(scratch, scratch, kHoleNaNInt64);
__ DeoptimizeIfZero(scratch, instr, "hole");

It should assemble to just three instructions, since kHoleNaNInt64 is
representable as a logical immediate:

  ldr x16, [mem_op]
  eor x16, x16, #0x7ff000007ff00000
  cbz x16, deopt_label

   }
 }