feat(tvix/eval): Don't emit OpForce for non-thunk constants

In the compiler, skip emitting an OpForce if the last op was an
OpConstant for a non-thunk constant. This gives a small (~1% on my
machine) perf boost, eg when evaluating hello.outPath:

    ❯ hyperfine \
        "./before --no-warnings -E '(import <nixpkgs> {}).hello.outPath'" \
        "./after --no-warnings -E '(import <nixpkgs> {}).hello.outPath'"
    Benchmark 1: ./before --no-warnings -E '(import <nixpkgs> {}).hello.outPath'
      Time (mean ± σ):      1.151 s ±  0.022 s    [User: 1.003 s, System: 0.151 s]
      Range (min … max):    1.123 s …  1.184 s    10 runs

    Benchmark 2: ./after --no-warnings -E '(import <nixpkgs> {}).hello.outPath'
      Time (mean ± σ):      1.140 s ±  0.022 s    [User: 0.989 s, System: 0.152 s]
      Range (min … max):    1.115 s …  1.175 s    10 runs

    Summary
      ./after --no-warnings -E '(import <nixpkgs> {}).hello.outPath' ran
        1.01 ± 0.03 times faster than ./before --no-warnings -E '(import <nixpkgs> {}).hello.outPath'

Change-Id: I2105fd431d4bad699087907e16c789418e9a4062
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10714
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
This commit is contained in:
Aspen Smith 2024-01-30 14:21:53 -05:00 committed by aspen
parent 25f0920025
commit 8caa097ba8
3 changed files with 26 additions and 0 deletions

View file

@ -70,6 +70,11 @@ impl Chunk {
self.spans[0].span
}
/// Return a reference to the last op in the chunk, if any
pub fn last_op(&self) -> Option<&OpCode> {
self.code.last()
}
/// Pop the last operation from the chunk and clean up its tracked
/// span. Used when the compiler backtracks.
pub fn pop_op(&mut self) {
@ -90,6 +95,11 @@ impl Chunk {
ConstantIdx(idx)
}
/// Return a reference to the constant at the given [`ConstantIdx`]
pub fn get_constant(&self, constant: ConstantIdx) -> Option<&Value> {
self.constants.get(constant.0)
}
// Span tracking implementation
fn push_span(&mut self, span: codemap::Span, start: usize) {

View file

@ -1457,6 +1457,15 @@ impl Compiler<'_> {
}
fn emit_force<N: ToSpan>(&mut self, node: &N) {
if let Some(&OpCode::OpConstant(c)) = self.chunk().last_op() {
if !self.chunk().get_constant(c).unwrap().is_thunk() {
// Optimization: Don't emit a force op for non-thunk constants, since they don't
// need one!
// TODO: this is probably doable for more ops (?)
return;
}
}
self.push_op(OpCode::OpForce, node);
}

View file

@ -724,6 +724,13 @@ impl Value {
gen_is!(is_attrs, Value::Attrs(_));
gen_is!(is_catchable, Value::Catchable(_));
/// Returns `true` if the value is a [`Thunk`].
///
/// [`Thunk`]: Value::Thunk
pub fn is_thunk(&self) -> bool {
matches!(self, Self::Thunk(..))
}
/// Compare `self` against other using (fallible) Nix ordering semantics.
///
/// The function is intended to be used from within other generator