bug: completely remove code generated by disabled VM_BUG_ON()

Even if CONFIG_DEBUG_VM=n gcc genereates code for some VM_BUG_ON()

for example VM_BUG_ON(!PageCompound(page) || !PageHead(page)); in
do_huge_pmd_wp_page() generates 114 bytes of code.

But they mostly disappears when I split this VM_BUG_ON into two:

-VM_BUG_ON(!PageCompound(page) || !PageHead(page));
+VM_BUG_ON(!PageCompound(page));
+VM_BUG_ON(!PageHead(page));

weird... but anyway after this patch code disappears completely.

add/remove: 0/0 grow/shrink: 7/97 up/down: 135/-1784 (-1649)

Signed-off-by: Konstantin Khlebnikov <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Geert Uytterhoeven <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: Cong Wang <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/mmdebug.h

···
 #ifdef CONFIG_DEBUG_VM
 #define VM_BUG_ON(cond) BUG_ON(cond)
 #else
-#define VM_BUG_ON(cond) do { (void)(cond); } while (0)
+#define VM_BUG_ON(cond) BUILD_BUG_ON_INVALID(cond)
 #endif
 
 #ifdef CONFIG_DEBUG_VIRTUAL