From: Jan Beulich <jbeulich@suse.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Andrew Cooper" <andrew.cooper3@citrix.com>,
"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>,
"George Dunlap" <george.dunlap@citrix.com>
Subject: [PATCH v2 2/2] x86/p2m: aid the compiler in folding p2m_is_...()
Date: Thu, 23 Jun 2022 13:54:40 +0200 [thread overview]
Message-ID: <7cce89f4-962e-bfbe-7d30-18fea7515bed@suse.com> (raw)
In-Reply-To: <5d6c927e-7d7c-5754-e7eb-65d1e70f6222@suse.com>
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.
---
v2: Re-base over change to earlier patch.
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -379,7 +379,7 @@ 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)) &&
!mem_sharing_is_fork(p2m->domain) )
return NULL;
}
@@ -568,7 +568,7 @@ p2m_remove_entry(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));
next prev parent reply other threads:[~2022-06-23 11:55 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-23 11:52 [PATCH v2 0/2] x86/p2m: type checking adjustments Jan Beulich
2022-06-23 11:53 ` [PATCH v2 1/2] x86/p2m: make p2m_get_page_from_gfn() handle grant case correctly Jan Beulich
2024-02-08 6:32 ` George Dunlap
2024-02-08 8:02 ` Jan Beulich
2024-02-08 8:09 ` George Dunlap
2022-06-23 11:54 ` Jan Beulich [this message]
2024-02-01 13:32 ` [PATCH v2 2/2] x86/p2m: aid the compiler in folding p2m_is_...() George Dunlap
2024-02-01 14:14 ` Jan Beulich
2024-02-07 3:07 ` George Dunlap
2024-02-07 8:50 ` Jan Beulich
2024-02-12 14:22 ` Jan Beulich
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