[committed] libstdc++: Use __builtin_expect in __dynamic_cast
Jonathan Wakely
jwakely@redhat.com
Mon Aug 23 13:48:09 GMT 2021
The null pointer check is never needed for correct code, only to
gracefully handle undefined cases. Add __builtin_expect to be sure that
we don't pessimize the valid uses.
libstdc++-v3/ChangeLog:
* libsupc++/dyncast.cc (__dynamic_cast): Add __builtin_expect to
precondition check.
Tested powerpc64le-linux. Committed to trunk.
-------------- next part --------------
commit da6ce351069bda74d814b723934008d75bd4e8b0
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Aug 23 13:12:24 2021
libstdc++: Use __builtin_expect in __dynamic_cast
The null pointer check is never needed for correct code, only to
gracefully handle undefined cases. Add __builtin_expect to be sure that
we don't pessimize the valid uses.
libstdc++-v3/ChangeLog:
* libsupc++/dyncast.cc (__dynamic_cast): Add __builtin_expect to
precondition check.
diff --git a/libstdc++-v3/libsupc++/dyncast.cc b/libstdc++-v3/libsupc++/dyncast.cc
index f8f707ee4d4..a1138d04f6d 100644
--- a/libstdc++-v3/libsupc++/dyncast.cc
+++ b/libstdc++-v3/libsupc++/dyncast.cc
@@ -47,9 +47,9 @@ __dynamic_cast (const void *src_ptr, // object started from
const __class_type_info *dst_type, // desired target type
ptrdiff_t src2dst) // how src and dst are related
{
- if (!src_ptr)
- /* Handle precondition violations gracefully. */
- return NULL;
+ if (__builtin_expect(!src_ptr, 0))
+ return NULL; // Handle precondition violations gracefully.
+
const void *vtable = *static_cast <const void *const *> (src_ptr);
const vtable_prefix *prefix =
(adjust_pointer <vtable_prefix>
@@ -70,7 +70,7 @@ __dynamic_cast (const void *src_ptr, // object started from
(whole_vtable, -ptrdiff_t (offsetof (vtable_prefix, origin))));
if (whole_prefix->whole_type != whole_type)
return NULL;
-
+
whole_type->__do_dyncast (src2dst, __class_type_info::__contained_public,
dst_type, whole_ptr, src_type, src_ptr, result);
if (!result.dst_ptr)
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