Fix mozilla regress-398085-01 failure on windows.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 41441f5efe422c5d738459e05e487b16512f584b..7a601cf39bcfe24e96edc79bed8cde655f329b52 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -137,6 +137,16 @@ void LCodeGen::Comment(const char* format, ...) {
 }
 
 
+#ifdef _MSC_VER
+void LCodeGen::MakeSureStackPagesMapped(int offset) {
+  const int kPageSize = 4 * KB;
+  for (offset -= kPageSize; offset > 0; offset -= kPageSize) {
+    __ mov(Operand(esp, offset), eax);
+  }
+}
+#endif
+
+
 bool LCodeGen::GeneratePrologue() {
   ASSERT(is_generating());
 
@@ -226,6 +236,9 @@ bool LCodeGen::GeneratePrologue() {
     } else {
       if (FLAG_debug_code) {
         __ sub(Operand(esp), Immediate(slots * kPointerSize));
+#ifdef _MSC_VER
+        MakeSureStackPagesMapped(slots * kPointerSize);
+#endif
         __ push(eax);
         __ mov(Operand(eax), Immediate(slots));
         Label loop;
@@ -238,15 +251,7 @@ bool LCodeGen::GeneratePrologue() {
       } else {
         __ sub(Operand(esp), Immediate(slots * kPointerSize));
 #ifdef _MSC_VER
-        // On windows, you may not access the stack more than one page below
-        // the most recently mapped page. To make the allocated area randomly
-        // accessible, we write to each page in turn (the value is irrelevant).
-        const int kPageSize = 4 * KB;
-        for (int offset = slots * kPointerSize - kPageSize;
-             offset > 0;
-             offset -= kPageSize) {
-          __ mov(Operand(esp, offset), eax);
-        }
+        MakeSureStackPagesMapped(slots * kPointerSize);
 #endif
       }