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 182a76ce2b99e1b5bf9e122ba1c2a134b9c9003d..d580f28cb6083f5939aec909573cfee35a3ddbb3 100644
--- a/Source/wtf/PageAllocator.cpp
+++ b/Source/wtf/PageAllocator.cpp
@@ -58,6 +58,28 @@
 
 namespace WTF {
 
+#if OS(WIN)
+
+static bool shouldUseAddressHint()
+{
+#if !CPU(X86_64)
+    static bool architectureKnown = false;
+    static bool useHint = true;
+    if (!architectureKnown) {
+        SYSTEM_INFO systemInfo = { 0 };
+        ::GetNativeSystemInfo(&systemInfo);
+        if (systemInfo.wProcessorArchitecture == PROCESSOR_ARCHITECTURE_INTEL)

[Chris Evans, 2014/07/18 18:03:47]

I don't understand this. It sounds from the CL description that you're trying to
distinguish between a 2G/2G split vs. 3G/1G user/kernel split? If this above
code is the magic to do that, it might use a comment.

[Tom Sepez, 2014/07/18 18:10:06]

Exactly.  Will add comment.

+            useHint = false;
+        architectureKnown = true;
+    }
+    return useHint;
+#else // !CPU(X86_64)
+    return true;
+#endif // !CPU(X86_64)
+}
+
+#endif // OS(WIN)
+
 // This simple internal function wraps the OS-specific page allocation call so
 // that it behaves consistently: the address is a hint and if it cannot be used,
 // the allocation will be placed elsewhere.
@@ -65,9 +87,10 @@ static void* systemAllocPages(void* addr, size_t len)
 {
     ASSERT(!(len & kPageAllocationGranularityOffsetMask));
     ASSERT(!(reinterpret_cast<uintptr_t>(addr) & kPageAllocationGranularityOffsetMask));
-    void* ret;
+    void* ret = 0;
 #if OS(WIN)
-    ret = VirtualAlloc(addr, len, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
+    if (shouldUseAddressHint())
+        ret = VirtualAlloc(addr, len, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
     if (!ret)
         ret = VirtualAlloc(0, len, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
 #else