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One more small optimization: Where possible, for loops that do a search and then try to break out of the loop early, eliminate the attempt to break out of the loop after the last search. And with that, I'm declaring __dynamic_cast done. Though if anyone sees any problems, has suggestions for improvements, or wants to contribute some test cases, that is certainly welcome feedback.

Browse Source 
llvm-svn: 148246
This commit is contained in:
Howard Hinnant 2012-01-16 18:21:05 +00:00
parent 7c4dcf4b93
commit b24c9441d1
3 changed files with 91 additions and 82 deletions
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159
libcxxabi/src/private_typeinfo.cpp
View File

@ -282,12 +282,8 @@ __class_type_info::process_static_type_below_dst(__dynamic_cast_info* info,
const void* current_ptr,
int path_below) const
{
// Record that we found a static_type
info->found_any_static_type = true; // TODO: Consider removing, no one is currently listening
if (current_ptr == info->static_ptr)
{
// Record that we found (static_ptr, static_type)
info->found_our_static_ptr = true; // TODO: Consider removing, no one is currently listening
// Record the most public path from (dynamic_ptr, dynamic_type) to
// (static_ptr, static_type)
if (info->path_dynamic_ptr_to_static_ptr != public_path)
@ -424,59 +420,64 @@ __vmi_class_type_info::search_below_dst(__dynamic_cast_info* info,
{
// This is not a static_type and not a dst_type.
const Iter e = __base_info + __base_count;
if ((__flags & __diamond_shaped_mask) || info->number_to_static_ptr == 1)
Iter p = __base_info;
p->search_below_dst(info, current_ptr, path_below);
if (++p < e)
{
// If there are multiple paths to a base above from here, or if
// a dst_type pointing to (static_ptr, static_type) has been found,
// then there is no way to break out of this loop early unless
// something below detects the search is done.
for (Iter p = __base_info; p < e; ++p)
if ((__flags & __diamond_shaped_mask) || info->number_to_static_ptr == 1)
{
p->search_below_dst(info, current_ptr, path_below);
if (info->search_done)
break;
// If there are multiple paths to a base above from here, or if
// a dst_type pointing to (static_ptr, static_type) has been found,
// then there is no way to break out of this loop early unless
// something below detects the search is done.
do
{
if (info->search_done)
break;
p->search_below_dst(info, current_ptr, path_below);
} while (++p < e);
}
}
else if (__flags & __non_diamond_repeat_mask)
{
// There are not multiple paths to any base class from here and a
// dst_type pointing to (static_ptr, static_type) has not yet been
// found.
for (Iter p = __base_info; p < e; ++p)
else if (__flags & __non_diamond_repeat_mask)
{
p->search_below_dst(info, current_ptr, path_below);
if (info->search_done)
break;
// If we just found a dst_type with a public path to (static_ptr, static_type),
// then the only reason to continue the search is to make sure
// no other dst_type points to (static_ptr, static_type).
// If !diamond, then we don't need to search here.
if (info->number_to_static_ptr == 1 &&
info->path_dst_ptr_to_static_ptr == public_path)
break;
// There are not multiple paths to any base class from here and a
// dst_type pointing to (static_ptr, static_type) has not yet been
// found.
do
{
if (info->search_done)
break;
// If we just found a dst_type with a public path to (static_ptr, static_type),
// then the only reason to continue the search is to make sure
// no other dst_type points to (static_ptr, static_type).
// If !diamond, then we don't need to search here.
if (info->number_to_static_ptr == 1 &&
info->path_dst_ptr_to_static_ptr == public_path)
break;
p->search_below_dst(info, current_ptr, path_below);
} while (++p < e);
}
}
else
{
// There are no repeated types above this node.
// There are no nodes with multiple parents above this node.
// no dst_type has been found to (static_ptr, static_type)
for (Iter p = __base_info; p < e; ++p)
else
{
p->search_below_dst(info, current_ptr, path_below);
if (info->search_done)
break;
// If we just found a dst_type with a public path to (static_ptr, static_type),
// then the only reason to continue the search is to make sure sure
// no other dst_type points to (static_ptr, static_type).
// If !diamond, then we don't need to search here.
// if we just found a dst_type with a private path to (static_ptr, static_type),
// then we're only looking for a public path to (static_ptr, static_type)
// and to check for other dst_types.
// If !diamond & !repeat, then there is not a pointer to (static_ptr, static_type)
// and not a dst_type under here.
if (info->number_to_static_ptr == 1)
break;
// There are no repeated types above this node.
// There are no nodes with multiple parents above this node.
// no dst_type has been found to (static_ptr, static_type)
do
{
if (info->search_done)
break;
// If we just found a dst_type with a public path to (static_ptr, static_type),
// then the only reason to continue the search is to make sure sure
// no other dst_type points to (static_ptr, static_type).
// If !diamond, then we don't need to search here.
// if we just found a dst_type with a private path to (static_ptr, static_type),
// then we're only looking for a public path to (static_ptr, static_type)
// and to check for other dst_types.
// If !diamond & !repeat, then there is not a pointer to (static_ptr, static_type)
// and not a dst_type under here.
if (info->number_to_static_ptr == 1)
break;
p->search_below_dst(info, current_ptr, path_below);
} while (++p < e);
}
}
}
@ -640,33 +641,41 @@ __vmi_class_type_info::search_above_dst(__dynamic_cast_info* info,
// 3. We can prove that there is no public path to (static_ptr, static_type)
// above here.
const Iter e = __base_info + __base_count;
for (Iter p = __base_info; p < e; ++p)
Iter p = __base_info;
// Zero out found flags
info->found_our_static_ptr = false;
info->found_any_static_type = false;
p->search_above_dst(info, dst_ptr, current_ptr, path_below);
if (++p < e)
{
// Zero out found flags
info->found_our_static_ptr = false;
info->found_any_static_type = false;
p->search_above_dst(info, dst_ptr, current_ptr, path_below);
if (info->search_done)
break;
if (info->found_our_static_ptr)
do
{
// If we found what we're looking for, stop looking above.
if (info->path_dst_ptr_to_static_ptr == public_path)
if (info->search_done)
break;
// We found a private path to (static_ptr, static_type)
// If there is no diamond then there is only one path
// to (static_ptr, static_type) from here and we just found it.
if (!(__flags & __diamond_shaped_mask))
break;
}
else if (info->found_any_static_type)
{
// If we found a static_type that isn't the one we're looking
// for, and if there are no repeated types above here,
// then stop looking.
if (!(__flags & __non_diamond_repeat_mask))
break;
}
if (info->found_our_static_ptr)
{
// If we found what we're looking for, stop looking above.
if (info->path_dst_ptr_to_static_ptr == public_path)
break;
// We found a private path to (static_ptr, static_type)
// If there is no diamond then there is only one path
// to (static_ptr, static_type) from here and we just found it.
if (!(__flags & __diamond_shaped_mask))
break;
}
else if (info->found_any_static_type)
{
// If we found a static_type that isn't the one we're looking
// for, and if there are no repeated types above here,
// then stop looking.
if (!(__flags & __non_diamond_repeat_mask))
break;
}
// Zero out found flags
info->found_our_static_ptr = false;
info->found_any_static_type = false;
p->search_above_dst(info, dst_ptr, current_ptr, path_below);
} while (++p < e);
}
// Restore flags
info->found_our_static_ptr = found_our_static_ptr;

8
libcxxabi/test/dynamic_cast_stress.cpp
View File

@ -73,9 +73,9 @@ int main()
Timing results I'm seeing (median of 3 microseconds):
libc++abi gcc's dynamic_cast
B<Width/2, Depth> -O3 50.694 93.190 libc++abi 84% faster
B<Width/2, Depth> -Os 55.235 94.103 libc++abi 70% faster
A<Width, Depth> -O3 14.895 33.134 libc++abi 122% faster
A<Width, Depth> -Os 16.515 31.553 libc++abi 91% faster
B<Width/2, Depth> -O3 48.334 93.190 libc++abi 93% faster
B<Width/2, Depth> -Os 58.535 94.103 libc++abi 61% faster
A<Width, Depth> -O3 11.515 33.134 libc++abi 188% faster
A<Width, Depth> -Os 12.631 31.553 libc++abi 150% faster
*/

6
libcxxabi/www/spec.html
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@ -824,9 +824,9 @@ Called from the compiler.
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