Re-land: 178586 Avoid fragmenting address space on small windows systems.

Source/wtf/PageAllocator.cpp

Index: Source/wtf/PageAllocator.cpp
diff --git a/Source/wtf/PageAllocator.cpp b/Source/wtf/PageAllocator.cpp
index fda703aec591d619f15f31d7d7f3fb0740bac9a6..a6b27d424fa6a183493555ef9f36a4dd31ff8480 100644
--- a/Source/wtf/PageAllocator.cpp
+++ b/Source/wtf/PageAllocator.cpp
@@ -62,18 +62,21 @@ namespace WTF {
 
 static bool shouldUseAddressHint()
 {
-#if CPU(32BIT)
+#if !CPU(64BIT)

[Chris Evans, 2014/11/14 01:48:16]

I kind of like having the symmetry of both CPU(32BIT) and CPU(64BIT) to be
honest. My vote is to keep CPU(32BIT).

     // When running 32-bit processes under 32-bit Windows, the userspace is
     // limited to 2 GB, and we risk fragmenting it badly if we allow further
     // randomization via our address hint. On the other hand, if the process
     // is running under WOW64, then it has at least 3 GB available (and likely
     // 4 GB depending upon the OS version), and we want use the additional
     // randomness.
-    // TODO(tsepez): presently disabled due to IsWow64Process() compatibility.
-    return true;
-#else // CPU(32BIT)
+    static BOOL bIsWow64 = -1;
+    if (bIsWow64 == -1) {
+        IsWow64Process(GetCurrentProcess(), &bIsWow64);
+    }
+    return !!bIsWow64;
+#else // !CPU(64BIT)
     return true;
-#endif // CPU(32BIT)
+#endif // !CPU(64BIT)
 }
 
 #endif // OS(WIN)