diff mbox series

[RFC,2/2] x86/p2m: aid the compiler in folding p2m_is_...()

Message ID 0273a69d-0c51-cbd6-e5e9-da861d14cb06@suse.com (mailing list archive)
State New, archived
Headers show
Series x86/p2m: type checking adjustments | expand

Commit Message

Jan Beulich Feb. 23, 2022, 3:15 p.m. UTC 
By using | instead of || or (in the negated form) && chances increase
for the compiler to recognize that both predicates can actually be
folded into an expression requiring just a single branch (via OR-ing
together the respective P2M_*_TYPES constants).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
RFC: The 3-way checks look to be a general problem for gcc, but even in
     some 2-way cases it doesn't manage to fold the expressions. Hence
     it's worth considering to go farther with this transformation, as
     long as the idea isn't disliked in general.
diff mbox series

Patch

--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -606,7 +606,7 @@  struct page_info *p2m_get_page_from_gfn(
             return page;
 
         /* Error path: not a suitable GFN at all */
-        if ( !p2m_is_ram(*t) && !p2m_is_paging(*t) && !p2m_is_pod(*t) &&
+        if ( !(p2m_is_ram(*t) | p2m_is_paging(*t) | p2m_is_pod(*t)) &&
              (!p2m_is_shared(*t) || !(q & P2M_UNSHARE)) &&
              !mem_sharing_is_fork(p2m->domain) )
             return NULL;
@@ -840,7 +840,7 @@  p2m_remove_page(struct p2m_domain *p2m,
     for ( i = 0; i < (1UL << page_order); ++i )
     {
         p2m->get_entry(p2m, gfn_add(gfn, i), &t, &a, 0, NULL, NULL);
-        if ( !p2m_is_hole(t) && !p2m_is_special(t) && !p2m_is_shared(t) )
+        if ( !(p2m_is_hole(t) | p2m_is_special(t) | p2m_is_shared(t)) )
         {
             set_gpfn_from_mfn(mfn_x(mfn) + i, gfn_x(gfn) + i);
             paging_mark_pfn_dirty(p2m->domain, _pfn(gfn_x(gfn) + i));