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Rework Stringpool to not compute the hash code twice when adding a new 

string.
This commit is contained in:
Ian Lance Taylor 2007-12-05 22:56:51 +00:00
parent d688b66ee1
commit 987cc25110
2 changed files with 191 additions and 127 deletions
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214
gold/stringpool.cc
View File

@ -80,13 +80,12 @@ Stringpool_template<char>::string_length(const char* p)
return strlen(p);
}
// Equality comparison function.
// Compare two strings of arbitrary character type for equality.
template<typename Stringpool_char>
bool
Stringpool_template<Stringpool_char>::Stringpool_eq::operator()(
const Stringpool_char* s1,
const Stringpool_char* s2) const
Stringpool_template<Stringpool_char>::string_equal(const Stringpool_char* s1,
const Stringpool_char* s2)
{
while (*s1 != 0)
if (*s1++ != *s2++)
@ -94,62 +93,69 @@ Stringpool_template<Stringpool_char>::Stringpool_eq::operator()(
return *s2 == 0;
}
// Specialize equality comparison for char.
// Specialize string_equal for char.
template<>
bool
Stringpool_template<char>::Stringpool_eq::operator()(const char* s1,
const char* s2) const
inline bool
Stringpool_template<char>::string_equal(const char* s1, const char* s2)
{
return strcmp(s1, s2) == 0;
}
// Hash function.
// Equality comparison function for the hash table.
template<typename Stringpool_char>
inline bool
Stringpool_template<Stringpool_char>::Stringpool_eq::operator()(
const Hashkey& h1,
const Hashkey& h2) const
{
return (h1.hash_code == h2.hash_code
&& h1.length == h2.length
&& memcmp(h1.string, h2.string,
h1.length * sizeof(Stringpool_char)) == 0);
}
// Hash function. The length is in characters, not bytes.
template<typename Stringpool_char>
size_t
Stringpool_template<Stringpool_char>::Stringpool_hash::operator()(
const Stringpool_char* s) const
Stringpool_template<Stringpool_char>::string_hash(const Stringpool_char* s,
size_t length)
{
// Fowler/Noll/Vo (FNV) hash (type FNV-1a).
const unsigned char* p = reinterpret_cast<const unsigned char*>(s);
if (sizeof(size_t) > 4)
{
size_t result = static_cast<size_t>(14695981039346656037ULL);
while (*s != 0)
for (size_t i = 0; i < length * sizeof(Stringpool_char); ++i)
{
const char* p = reinterpret_cast<const char*>(s);
for (size_t i = 0; i < sizeof(Stringpool_char); ++i)
{
result ^= (size_t) *p++;
result *= 1099511628211ULL;
}
++s;
result ^= static_cast<size_t>(*p++);
result *= 1099511628211ULL;
}
return result;
}
else
{
size_t result = 2166136261UL;
while (*s != 0)
for (size_t i = 0; i < length * sizeof(Stringpool_char); ++i)
{
const char* p = reinterpret_cast<const char*>(s);
for (size_t i = 0; i < sizeof(Stringpool_char); ++i)
{
result ^= (size_t) *p++;
result *= 16777619UL;
}
++s;
result ^= static_cast<size_t>(*p++);
result *= 16777619UL;
}
return result;
}
}
// Add a string to the list of canonical strings. Return a pointer to
// the canonical string. If PKEY is not NULL, set *PKEY to the key.
// Add the string S to the list of canonical strings. Return a
// pointer to the canonical string. If PKEY is not NULL, set *PKEY to
// the key. LENGTH is the length of S in characters. Note that S may
// not be NUL terminated.
template<typename Stringpool_char>
const Stringpool_char*
Stringpool_template<Stringpool_char>::add_string(const Stringpool_char* s,
size_t len,
Key* pkey)
{
// We are in trouble if we've already computed the string offsets.
@ -162,7 +168,9 @@ Stringpool_template<Stringpool_char>::add_string(const Stringpool_char* s,
const size_t key_mult = 1024;
gold_assert(key_mult >= buffer_size);
size_t len = (string_length(s) + 1) * sizeof(Stringpool_char);
// Convert len to the number of bytes we need to allocate, including
// the null character.
len = (len + 1) * sizeof(Stringpool_char);
size_t alc;
bool front = true;
@ -181,7 +189,9 @@ Stringpool_template<Stringpool_char>::add_string(const Stringpool_char* s,
else
{
char* ret = psd->data + psd->len;
memcpy(ret, s, len);
memcpy(ret, s, len - sizeof(Stringpool_char));
memset(ret + len - sizeof(Stringpool_char), 0,
sizeof(Stringpool_char));
if (pkey != NULL)
*pkey = psd->index * key_mult + psd->len;
@ -194,7 +204,9 @@ Stringpool_template<Stringpool_char>::add_string(const Stringpool_char* s,
Stringdata *psd = reinterpret_cast<Stringdata*>(new char[alc]);
psd->alc = alc - sizeof(Stringdata);
memcpy(psd->data, s, len);
memcpy(psd->data, s, len - sizeof(Stringpool_char));
memset(psd->data + len - sizeof(Stringpool_char), 0,
sizeof(Stringpool_char));
psd->len = len;
psd->index = this->next_index_;
++this->next_index_;
@ -217,42 +229,39 @@ const Stringpool_char*
Stringpool_template<Stringpool_char>::add(const Stringpool_char* s, bool copy,
Key* pkey)
{
// FIXME: This will look up the entry twice in the hash table. The
// problem is that we can't insert S before we canonicalize it. I
// don't think there is a way to handle this correctly with
// unordered_map, so this should be replaced with custom code to do
// what we need, which is to return the empty slot.
typedef std::pair<typename String_set_type::iterator, bool> Insert_type;
typename String_set_type::const_iterator p = this->string_set_.find(s);
if (p != this->string_set_.end())
if (!copy)
{
// When we don't need to copy the string, we can call insert
// directly.
const Key k = this->next_uncopied_key_;
const off_t ozero = 0;
std::pair<Hashkey, Hashval> element(Hashkey(s),
std::make_pair(k, ozero));
Insert_type ins = this->string_set_.insert(element);
typename String_set_type::const_iterator p = ins.first;
if (ins.second)
{
// We just added the string. The key value has now been
// used.
--this->next_uncopied_key_;
}
else
{
gold_assert(k != p->second.first);
}
if (pkey != NULL)
*pkey = p->second.first;
return p->first;
return p->first.string;
}
Key k;
const Stringpool_char* ret;
if (copy)
ret = this->add_string(s, &k);
else
{
ret = s;
k = this->next_uncopied_key_;
--this->next_uncopied_key_;
}
const off_t ozero = 0;
std::pair<const Stringpool_char*, Val> element(ret,
std::make_pair(k, ozero));
std::pair<typename String_set_type::iterator, bool> ins =
this->string_set_.insert(element);
gold_assert(ins.second);
if (pkey != NULL)
*pkey = k;
return ret;
return this->add_prefix(s, string_length(s), pkey);
}
// Add a prefix of a string to a string pool.
@ -263,10 +272,36 @@ Stringpool_template<Stringpool_char>::add_prefix(const Stringpool_char* s,
size_t len,
Key* pkey)
{
// FIXME: This implementation should be rewritten when we rewrite
// the hash table to avoid copying.
std::basic_string<Stringpool_char> st(s, len);
return this->add(st.c_str(), true, pkey);
// When adding an entry, this will look it up twice in the hash
// table. The problem is that we can't insert S before we
// canonicalize it by copying it into the canonical list. The hash
// code will only be computed once, so this isn't all that
// expensive.
Hashkey hk(s, len);
typename String_set_type::const_iterator p = this->string_set_.find(hk);
if (p != this->string_set_.end())
{
if (pkey != NULL)
*pkey = p->second.first;
return p->first.string;
}
Key k;
hk.string = this->add_string(s, len, &k);
// The contents of the string stay the same, so we don't need to
// adjust hk.hash_code or hk.length.
const off_t ozero = 0;
std::pair<Hashkey, Hashval> element(hk, std::make_pair(k, ozero));
typedef std::pair<typename String_set_type::iterator, bool> Insert_type;
Insert_type ins = this->string_set_.insert(element);
gold_assert(ins.second);
if (pkey != NULL)
*pkey = k;
return hk.string;
}
template<typename Stringpool_char>
@ -274,14 +309,15 @@ const Stringpool_char*
Stringpool_template<Stringpool_char>::find(const Stringpool_char* s,
Key* pkey) const
{
typename String_set_type::const_iterator p = this->string_set_.find(s);
Hashkey hk(s);
typename String_set_type::const_iterator p = this->string_set_.find(hk);
if (p == this->string_set_.end())
return NULL;
if (pkey != NULL)
*pkey = p->second.first;
return p->first;
return p->first.string;
}
// Comparison routine used when sorting into an ELF strtab. We want
@ -301,10 +337,12 @@ Stringpool_template<Stringpool_char>::Stringpool_sort_comparison::operator()(
const Stringpool_sort_info& sort_info1,
const Stringpool_sort_info& sort_info2) const
{
const Stringpool_char* s1 = sort_info1.it->first;
const Stringpool_char* s2 = sort_info2.it->first;
const size_t len1 = sort_info1.string_length;
const size_t len2 = sort_info2.string_length;
const Hashkey& h1(sort_info1->first);
const Hashkey& h2(sort_info2->first);
const Stringpool_char* s1 = h1.string;
const Stringpool_char* s2 = h2.string;
const size_t len1 = h1.length;
const size_t len2 = h2.length;
const size_t minlen = len1 < len2 ? len1 : len2;
const Stringpool_char* p1 = s1 + len1 - 1;
const Stringpool_char* p2 = s2 + len2 - 1;
@ -359,12 +397,12 @@ Stringpool_template<Stringpool_char>::set_string_offsets()
curr != this->string_set_.end();
curr++)
{
if (this->zero_null_ && curr->first[0] == 0)
if (this->zero_null_ && curr->first.string[0] == 0)
curr->second.second = 0;
else
{
curr->second.second = offset;
offset += (string_length(curr->first) + 1) * charsize;
offset += (curr->first.length + 1) * charsize;
}
}
}
@ -378,7 +416,7 @@ Stringpool_template<Stringpool_char>::set_string_offsets()
for (typename String_set_type::iterator p = this->string_set_.begin();
p != this->string_set_.end();
++p)
v.push_back(Stringpool_sort_info(p, string_length(p->first)));
v.push_back(Stringpool_sort_info(p));
std::sort(v.begin(), v.end(), Stringpool_sort_comparison());
@ -387,19 +425,21 @@ Stringpool_template<Stringpool_char>::set_string_offsets()
curr != v.end();
last = curr++)
{
if (this->zero_null_ && curr->it->first[0] == 0)
curr->it->second.second = 0;
if (this->zero_null_ && (*curr)->first.string[0] == 0)
(*curr)->second.second = 0;
else if (last != v.end()
&& is_suffix(curr->it->first, curr->string_length,
last->it->first, last->string_length))
curr->it->second.second = (last->it->second.second
+ ((last->string_length
- curr->string_length)
* charsize));
&& is_suffix((*curr)->first.string,
(*curr)->first.length,
(*last)->first.string,
(*last)->first.length))
(*curr)->second.second = ((*last)->second.second
+ (((*last)->first.length
- (*curr)->first.length)
* charsize));
else
{
curr->it->second.second = offset;
offset += (curr->string_length + 1) * charsize;
(*curr)->second.second = offset;
offset += ((*curr)->first.length + 1) * charsize;
}
}
}
@ -439,9 +479,9 @@ Stringpool_template<Stringpool_char>::write_to_buffer(unsigned char* buffer,
p != this->string_set_.end();
++p)
{
const int len = (string_length(p->first) + 1) * sizeof(Stringpool_char);
const int len = (p->first.length + 1) * sizeof(Stringpool_char);
gold_assert(p->second.second + len <= this->strtab_size_);
memcpy(buffer + p->second.second, p->first, len);
memcpy(buffer + p->second.second, p->first.string, len);
}
}

104
gold/stringpool.h
View File

@ -161,6 +161,15 @@ class Stringpool_template
static size_t
string_length(const Stringpool_char*);
// Return whether two strings are equal.
static bool
string_equal(const Stringpool_char*, const Stringpool_char*);
// Compute a hash code for a string. LENGTH is the length of the
// string in characters.
static size_t
string_hash(const Stringpool_char*, size_t length);
// We store the actual data in a list of these buffers.
struct Stringdata
{
@ -176,56 +185,71 @@ class Stringpool_template
// Copy a string into the buffers, returning a canonical string.
const Stringpool_char*
add_string(const Stringpool_char*, Key*);
// Hash function.
struct Stringpool_hash
{
size_t
operator()(const Stringpool_char*) const;
};
// Equality comparison function for hash table.
struct Stringpool_eq
{
bool
operator()(const Stringpool_char* p1, const Stringpool_char* p2) const;
};
add_string(const Stringpool_char*, size_t, Key*);
// Return whether s1 is a suffix of s2.
static bool
is_suffix(const Stringpool_char* s1, size_t len1,
const Stringpool_char* s2, size_t len2);
// The hash table is a map from string names to a pair of Key and
// string table offsets. We only use the offsets if we turn this
// into an string table section.
typedef std::pair<Key, off_t> Val;
#ifdef HAVE_TR1_UNORDERED_SET
typedef Unordered_map<const Stringpool_char*, Val, Stringpool_hash,
Stringpool_eq,
std::allocator<std::pair<const Stringpool_char* const,
Val> >,
true> String_set_type;
#else
typedef Unordered_map<const Stringpool_char*, Val, Stringpool_hash,
Stringpool_eq> String_set_type;
#endif
// Comparison routine used when sorting into a string table. We
// store string-sizes in the sort-vector so we don't have to
// recompute them log(n) times as we sort.
struct Stringpool_sort_info
// The hash table key includes the string, the length of the string,
// and the hash code for the string. We put the hash code
// explicitly into the key so that we can do a find()/insert()
// sequence without having to recompute the hash. Computing the
// hash code is a significant user of CPU time in the linker.
struct Hashkey
{
typename String_set_type::iterator it;
size_t string_length;
Stringpool_sort_info(typename String_set_type::iterator i, size_t s)
: it(i), string_length(s)
const Stringpool_char* string;
// Length is in characters, not bytes.
size_t length;
size_t hash_code;
// This goes in an STL container, so we need a default
// constructor.
Hashkey()
: string(NULL), length(0), hash_code(0)
{ }
// Note that these constructors are relatively expensive, because
// they compute the hash code.
Hashkey(const Stringpool_char* s)
: string(s), length(string_length(s)), hash_code(string_hash(s, length))
{ }
Hashkey(const Stringpool_char* s, size_t len)
: string(s), length(len), hash_code(string_hash(s, len))
{ }
};
// Hash function. This is trivial, since we have already computed
// the hash.
struct Stringpool_hash
{
size_t
operator()(const Hashkey& hk) const
{ return hk.hash_code; }
};
// Equality comparison function for hash table.
struct Stringpool_eq
{
bool
operator()(const Hashkey&, const Hashkey&) const;
};
// The hash table is a map from strings to a pair of Key and string
// table offsets. We only use the offsets if we turn this into an
// string table section.
typedef std::pair<Key, off_t> Hashval;
typedef Unordered_map<Hashkey, Hashval, Stringpool_hash,
Stringpool_eq> String_set_type;
// Comparison routine used when sorting into a string table.
typedef typename String_set_type::iterator Stringpool_sort_info;
struct Stringpool_sort_comparison
{
bool