Try aligning unboxed double array backing store in allocation or scavenge promotion.

src/v8globals.h

Index: src/v8globals.h
diff --git a/src/v8globals.h b/src/v8globals.h
index bfc5e2339048ca6863adb0f6ea89b8bd7594eaa1..52501a0b27a4d7691a972a73841aa718f296e69b 100644
--- a/src/v8globals.h
+++ b/src/v8globals.h
@@ -48,6 +48,13 @@ const intptr_t kObjectAlignmentMask = kObjectAlignment - 1;
 const intptr_t kPointerAlignment = (1 << kPointerSizeLog2);
 const intptr_t kPointerAlignmentMask = kPointerAlignment - 1;
 
+#if V8_HOST_ARCH_64_BIT

[Erik Corry, 2012/04/16 14:35:19]

Instead of the ifdef you could just set kDoubleAlignment to 8.

+const intptr_t kDoubleAlignment = kPointerAlignment;
+#else
+const intptr_t kDoubleAlignment = 2 * kPointerAlignment;
+#endif
+const intptr_t kDoubleAlignmentMask = kDoubleAlignment - 1;
+
 // Desired alignment for maps.
 #if V8_HOST_ARCH_64_BIT
 const intptr_t kMapAlignmentBits = kObjectAlignmentBits;