Use signaling NaN for holes in fixed double arrays.

build/toolchain.gypi

Index: build/toolchain.gypi
diff --git a/build/toolchain.gypi b/build/toolchain.gypi
index 56b2e338eed352f3b2a95c408ad7fdfdb39653bf..0443790649c81ad1770c15b371b2135e8c59b9a9 100644
--- a/build/toolchain.gypi
+++ b/build/toolchain.gypi
@@ -223,6 +223,11 @@
               }, {
                 # 'v8_target_arch!=target_arch'
                 # Target not built with an Arm CXX compiler (simulator build).
+                'cflags': [
+                  '-msse2',
+                  '-mfpmath=sse',
+                  '-mmmx',  # Allows mmintrin.h for MMX intrinsics.
+                ],
                 'conditions': [
                   [ 'arm_float_abi=="hard"', {
                     'defines': [
@@ -812,36 +817,6 @@
       ['(OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris" \
          or OS=="netbsd" or OS=="mac" or OS=="android" or OS=="qnx") and \
         v8_target_arch=="ia32"', {
-        # All floating-point computations on x87 happens in 80-bit
-        # precision.  Because the C and C++ language standards allow
-        # the compiler to keep the floating-point values in higher
-        # precision than what's specified in the source and doing so
-        # is more efficient than constantly rounding up to 64-bit or
-        # 32-bit precision as specified in the source, the compiler,
-        # especially in the optimized mode, tries very hard to keep
-        # values in x87 floating-point stack (in 80-bit precision)
-        # as long as possible. This has important side effects, that
-        # the real value used in computation may change depending on
-        # how the compiler did the optimization - that is, the value
-        # kept in 80-bit is different than the value rounded down to
-        # 64-bit or 32-bit. There are possible compiler options to
-        # make this behavior consistent (e.g. -ffloat-store would keep
-        # all floating-values in the memory, thus force them to be
-        # rounded to its original precision) but they have significant
-        # runtime performance penalty.
-        #
-        # -mfpmath=sse -msse2 makes the compiler use SSE instructions
-        # which keep floating-point values in SSE registers in its
-        # native precision (32-bit for single precision, and 64-bit
-        # for double precision values). This means the floating-point
-        # value used during computation does not change depending on
-        # how the compiler optimized the code, since the value is
-        # always kept in its specified precision.
-        #
-        # Refer to http://crbug.com/348761 for rationale behind SSE2
-        # being a minimum requirement for 32-bit Linux builds and
-        # http://crbug.com/313032 for an example where this has "bit"
-        # us in the past.
         'cflags': [
           '-msse2',
           '-mfpmath=sse',