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Store short strings in Values

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The vast majority of strings are < 16 bytes, and so can be stored
directly in a Value. This saves a heap allocation and an indirection.
This commit is contained in:
Eelco Dolstra 2019-04-23 12:20:27 +02:00
parent 2160258cc4
commit 742a8046de
10 changed files with 107 additions and 78 deletions
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63
src/libexpr/eval.cc
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@ -51,9 +51,10 @@ static void printValue(std::ostream & str, std::set<const Value *> & active, con
case tBool:
str << (v.boolean ? "true" : "false");
break;
case tString:
case tShortString:
case tLongString:
str << "\"";
for (const char * i = v.string.s; *i; i++)
for (const char * i = v.getString(); *i; i++)
if (*i == '\"' || *i == '\\') str << "\\" << *i;
else if (*i == '\n') str << "\\n";
else if (*i == '\r') str << "\\r";
@ -140,7 +141,8 @@ string showType(const Value & v)
switch (v.type) {
case tInt: return "an integer";
case tBool: return "a boolean";
case tString: return v.string.context ? "a string with context" : "a string";
case tShortString: return "a string";
case tLongString: return v.string.context ? "a string with context" : "a string";
case tPath: return "a path";
case tNull: return "null";
case tAttrs: return "a set";
@ -170,8 +172,7 @@ static Symbol getName(const AttrName & name, EvalState & state, Env & env)
} else {
Root<Value> nameValue;
name.expr->eval(state, env, nameValue);
state.forceStringNoCtx(nameValue);
return state.symbols.create(nameValue->string.s);
return state.symbols.create(state.forceStringNoCtx(nameValue));
}
}
@ -495,14 +496,23 @@ LocalNoInline(void addErrorPrefix(Error & e, const char * s, const string & s2,
void mkString(Value & v, const char * s)
{
mkStringNoCopy(v, dupString(s));
auto len = strlen(s); // FIXME: only need to know if > short
if (len < WORD_SIZE * 2) {
strcpy((char *) &v.string, s);
v.type = tShortString;
} else
mkStringNoCopy(v, dupString(s));
}
Value & mkString(Value & v, const string & s, const PathSet & context)
{
mkString(v, s.c_str());
v.setContext(context);
if (context.empty())
mkString(v, s.c_str());
else {
mkStringNoCopy(v, dupString(s.c_str()));
v.setContext(context);
}
return v;
}
@ -840,8 +850,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
state.forceValue(nameVal, i.pos);
if (nameVal->type == tNull)
continue;
state.forceStringNoCtx(nameVal);
Symbol nameSym = state.symbols.create(nameVal->string.s);
Symbol nameSym = state.symbols.create(state.forceStringNoCtx(nameVal));
Bindings::iterator j = v.attrs->find(nameSym);
if (j != v.attrs->end())
throwEvalError("dynamic attribute '%1%' at %2% already defined at %3%", nameSym, i.pos, *j->pos);
@ -1313,7 +1322,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
NixFloat nf = 0;
bool first = !forceString;
Tag firstType = tString;
Tag firstType = tLongString;
auto vTmp = state.allocValue();
@ -1325,7 +1334,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
since paths are copied when they are used in a derivation),
and none of the strings are allowed to have contexts. */
if (first) {
firstType = vTmp->type;
firstType = vTmp->isString() ? tLongString : vTmp->type;
first = false;
}
@ -1347,7 +1356,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
} else
throwEvalError("cannot add %1% to a float, at %2%", showType(vTmp), pos);
} else
s << state.coerceToString(pos, vTmp, context, false, firstType == tString);
s << state.coerceToString(pos, vTmp, context, false, firstType == tLongString);
}
if (firstType == tInt)
@ -1448,13 +1457,13 @@ void EvalState::forceFunction(Value & v, const Pos & pos)
string EvalState::forceString(Value & v, const Pos & pos)
{
forceValue(v, pos);
if (v.type != tString) {
if (!v.isString()) {
if (pos)
throwTypeError("value is %1% while a string was expected, at %2%", v, pos);
else
throwTypeError("value is %1% while a string was expected", v);
}
return string(v.string.s);
return string(v.getString()); // FIXME: don't copy
}
@ -1469,15 +1478,15 @@ string EvalState::forceString(Value & v, PathSet & context, const Pos & pos)
string EvalState::forceStringNoCtx(Value & v, const Pos & pos)
{
string s = forceString(v, pos);
if (v.string.context) {
if (v.type == tLongString && v.string.context) {
PathSet context;
v.getContext(context);
if (pos)
throwEvalError("the string '%1%' is not allowed to refer to a store path (such as '%2%'), at %3%",
v.string.s, *context.begin(), pos);
v.string._s, *context.begin(), pos);
else
throwEvalError("the string '%1%' is not allowed to refer to a store path (such as '%2%')",
v.string.s, *context.begin());
v.string._s, *context.begin());
}
return s;
}
@ -1489,8 +1498,8 @@ bool EvalState::isDerivation(Value & v)
Bindings::iterator i = v.attrs->find(sType);
if (i == v.attrs->end()) return false;
forceValue(*i->value);
if (i->value->type != tString) return false;
return strcmp(i->value->string.s, "derivation") == 0;
if (!i->value->isString()) return false;
return strcmp(i->value->getString(), "derivation") == 0;
}
@ -1501,9 +1510,9 @@ string EvalState::coerceToString(const Pos & pos, Value & v, PathSet & context,
string s;
if (v.type == tString) {
if (v.isString()) {
v.getContext(context);
return v.string.s;
return v.getString();
}
if (v.type == tPath) {
@ -1603,6 +1612,9 @@ bool EvalState::eqValues(Value & v1, Value & v2)
if (v1.type == tFloat && v2.type == tInt)
return v1.fpoint == v2.integer;
if (v1.isString())
return v2.isString() && strcmp(v1.getString(), v2.getString()) == 0;
// All other types are not compatible with each other.
if (v1.type != v2.type) return false;
@ -1614,9 +1626,6 @@ bool EvalState::eqValues(Value & v1, Value & v2)
case tBool:
return v1.boolean == v2.boolean;
case tString:
return strcmp(v1.string.s, v2.string.s) == 0;
case tPath:
return strcmp(v1.path, v2.path) == 0;
@ -1799,8 +1808,8 @@ size_t valueSize(Value & v)
size_t sz = sizeof(Value);
switch (v.type) {
case tString:
sz += doString(v.string.s);
case tLongString:
sz += doString(v.string._s);
break;
case tPath:
sz += doString(v.path);