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gdb/dwarf: use std::equal_range in cooked_index_shard::find

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Looking at `cooked_index_shard::find`, I thought that we could make a
small optimization: when finding the upper bound, we already know the
lower bound.  And we know that the upper bound is >= the lower bound.
So we could pass `lower` as the first argument of the `std::upper_bound`
call to cut the part of the search space that is below `lower`.

It then occured to me that what we do is basically what
`std::equal_range` is for, so why not use it.  Implementations of
`std::equal_range` are likely do to things as efficiently as possible.

Unfortunately, because `cooked_index_entry::compare` is sensitive to the
order of its parameters, we need to provide two different comparison
functions (just like we do know, to the lower_bound and upper_bound
calls).  But I think that the use of equal_range makes it clear what the
intent of the code is.

Regression tested using the various DWARF target boards on Debian 12.

Change-Id: Idfad812fb9abae1b942d81ad9976aeed7c2cf762
Approved-By: Tom Tromey <tom@tromey.com>
This commit is contained in:
Simon Marchi 2025-03-24 16:20:28 -04:00 committed by Simon Marchi
parent 8cbf7d2a47
commit ebfdb1089b
1 changed files with 19 additions and 16 deletions
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35
gdb/dwarf2/cooked-index.c
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@ -547,25 +547,28 @@ cooked_index_shard::finalize (const parent_map_map *parent_maps)
cooked_index_shard::range
cooked_index_shard::find (const std::string &name, bool completing) const
{
cooked_index_entry::comparison_mode mode = (completing
? cooked_index_entry::COMPLETE
: cooked_index_entry::MATCH);
auto lower = std::lower_bound (m_entries.cbegin (), m_entries.cend (), name,
[=] (const cooked_index_entry *entry,
const std::string &n)
struct comparator
{
return cooked_index_entry::compare (entry->canonical, n.c_str (), mode) < 0;
});
cooked_index_entry::comparison_mode mode;
auto upper = std::upper_bound (m_entries.cbegin (), m_entries.cend (), name,
[=] (const std::string &n,
const cooked_index_entry *entry)
{
return cooked_index_entry::compare (entry->canonical, n.c_str (), mode) > 0;
});
bool operator() (const cooked_index_entry *entry,
const char *name) const noexcept
{
return cooked_index_entry::compare (entry->canonical, name, mode) < 0;
}
return range (lower, upper);
bool operator() (const char *name,
const cooked_index_entry *entry) const noexcept
{
return cooked_index_entry::compare (entry->canonical, name, mode) > 0;
}
};
return std::make_from_tuple<range>
(std::equal_range (m_entries.cbegin (), m_entries.cend (), name.c_str (),
comparator { (completing
? cooked_index_entry::COMPLETE
: cooked_index_entry::MATCH) }));
}
/* See cooked-index.h. */