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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.
This commit is contained in:
Jonathan Wakely 2021-08-23 13:12:24 +01:00
parent bc97e736a5
commit da6ce35106
1 changed files with 4 additions and 4 deletions
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8
libstdc++-v3/libsupc++/dyncast.cc
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@ -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)