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don't use Symbols for strings

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string expressions by and large do not need the benefits a Symbol gives us,
instead they pollute the symbol table and cause unnecessary overhead for almost
all strings. the one place we can think of that benefits from them (attrpaths
with expressions) extracts the benefit in the parser, which we'll have to touch
anyway when changing ExprString to hold strings.

this gives a sizeable improvement on of 3-5% on all benchmarks we've run.

 before

  nix search --no-eval-cache --offline ../nixpkgs hello
    Time (mean ± σ):      8.844 s ±  0.045 s    [User: 6.750 s, System: 1.663 s]
    Range (min … max):    8.758 s …  8.922 s    20 runs

  nix eval -f ../nixpkgs/pkgs/development/haskell-modules/hackage-packages.nix
    Time (mean ± σ):     367.4 ms ±   3.3 ms    [User: 332.3 ms, System: 35.2 ms]
    Range (min … max):   364.0 ms … 375.2 ms    20 runs

  nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
    Time (mean ± σ):      2.810 s ±  0.030 s    [User: 2.517 s, System: 0.225 s]
    Range (min … max):    2.742 s …  2.854 s    20 runs

 after

  nix search --no-eval-cache --offline ../nixpkgs hello
    Time (mean ± σ):      8.533 s ±  0.068 s    [User: 6.485 s, System: 1.642 s]
    Range (min … max):    8.404 s …  8.657 s    20 runs

  nix eval -f ../nixpkgs/pkgs/development/haskell-modules/hackage-packages.nix
    Time (mean ± σ):     347.6 ms ±   3.1 ms    [User: 313.1 ms, System: 34.5 ms]
    Range (min … max):   343.3 ms … 354.6 ms    20 runs

  nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
    Time (mean ± σ):      2.709 s ±  0.032 s    [User: 2.414 s, System: 0.232 s]
    Range (min … max):    2.655 s …  2.788 s    20 runs
This commit is contained in:
pennae 2022-01-19 14:31:30 +01:00
parent 0a7746603e
commit 9ac836d1d6
2 changed files with 13 additions and 13 deletions
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4
src/libexpr/nixexpr.hh
View file

@ -110,9 +110,9 @@ struct ExprFloat : Expr
struct ExprString : Expr
{
Symbol s;
string s;
Value v;
ExprString(const Symbol & s) : s(s) { v.mkString(s); };
ExprString(std::string s) : s(std::move(s)) { v.mkString(this->s.data()); };
COMMON_METHODS
Value * maybeThunk(EvalState & state, Env & env);
};

22
src/libexpr/parser.y
View file

@ -166,7 +166,7 @@ static void addFormal(const Pos & pos, Formals * formals, const Formal & formal)
static Expr * stripIndentation(const Pos & pos, SymbolTable & symbols,
vector<std::pair<Pos, std::variant<Expr *, StringToken> > > & es)
{
if (es.empty()) return new ExprString(symbols.create(""));
if (es.empty()) return new ExprString("");
/* Figure out the minimum indentation. Note that by design
whitespace-only final lines are not taken into account. (So
@ -244,7 +244,7 @@ static Expr * stripIndentation(const Pos & pos, SymbolTable & symbols,
s2 = string(s2, 0, p + 1);
}
es2->emplace_back(i->first, new ExprString(symbols.create(s2)));
es2->emplace_back(i->first, new ExprString(s2));
};
for (; i != es.end(); ++i, --n) {
std::visit(overloaded { trimExpr, trimString }, i->second);
@ -434,7 +434,7 @@ expr_simple
$$ = new ExprCall(CUR_POS,
new ExprVar(data->symbols.create("__findFile")),
{new ExprVar(data->symbols.create("__nixPath")),
new ExprString(data->symbols.create(path))});
new ExprString(path)});
}
| URI {
static bool noURLLiterals = settings.isExperimentalFeatureEnabled(Xp::NoUrlLiterals);
@ -443,7 +443,7 @@ expr_simple
.msg = hintfmt("URL literals are disabled"),
.errPos = CUR_POS
});
$$ = new ExprString(data->symbols.create($1));
$$ = new ExprString(string($1));
}
| '(' expr ')' { $$ = $2; }
/* Let expressions `let {..., body = ...}' are just desugared
@ -458,19 +458,19 @@ expr_simple
;
string_parts
: STR { $$ = new ExprString(data->symbols.create($1)); }
: STR { $$ = new ExprString(string($1)); }
| string_parts_interpolated { $$ = new ExprConcatStrings(CUR_POS, true, $1); }
| { $$ = new ExprString(data->symbols.create("")); }
| { $$ = new ExprString(""); }
;
string_parts_interpolated
: string_parts_interpolated STR
{ $$ = $1; $1->emplace_back(makeCurPos(@2, data), new ExprString(data->symbols.create($2))); }
{ $$ = $1; $1->emplace_back(makeCurPos(@2, data), new ExprString(string($2))); }
| string_parts_interpolated DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(makeCurPos(@2, data), $3); }
| DOLLAR_CURLY expr '}' { $$ = new vector<std::pair<Pos, Expr *> >; $$->emplace_back(makeCurPos(@1, data), $2); }
| STR DOLLAR_CURLY expr '}' {
$$ = new vector<std::pair<Pos, Expr *> >;
$$->emplace_back(makeCurPos(@1, data), new ExprString(data->symbols.create($1)));
$$->emplace_back(makeCurPos(@1, data), new ExprString(string($1)));
$$->emplace_back(makeCurPos(@2, data), $3);
}
;
@ -524,7 +524,7 @@ attrs
{ $$ = $1;
ExprString * str = dynamic_cast<ExprString *>($2);
if (str) {
$$->push_back(AttrName(str->s));
$$->push_back(AttrName(data->symbols.create(str->s)));
delete str;
} else
throw ParseError({
@ -541,7 +541,7 @@ attrpath
{ $$ = $1;
ExprString * str = dynamic_cast<ExprString *>($3);
if (str) {
$$->push_back(AttrName(str->s));
$$->push_back(AttrName(data->symbols.create(str->s)));
delete str;
} else
$$->push_back(AttrName($3));
@ -551,7 +551,7 @@ attrpath
{ $$ = new vector<AttrName>;
ExprString *str = dynamic_cast<ExprString *>($1);
if (str) {
$$->push_back(AttrName(str->s));
$$->push_back(AttrName(data->symbols.create(str->s)));
delete str;
} else
$$->push_back(AttrName($1));