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Collect statistics about MIR optimizations #76769
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,165 @@ | ||
| //! # Support for collecting simple statistics | ||
| //! | ||
| //! Statistics are useful for collecting metrics from optimization passes, like | ||
| //! the number of simplifications performed. To avoid introducing overhead, the | ||
| //! collection of statistics is enabled only when rustc is compiled with | ||
| //! debug-assertions. | ||
| //! | ||
| //! Statistics are static variables defined in the module they are used, and | ||
| //! lazy registered in the global collector on the first use. Once registered, | ||
| //! the collector will obtain their values at the end of compilation process | ||
| //! when requested with -Zmir-opt-stats option. | ||
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| use parking_lot::{const_mutex, Mutex}; | ||
| use std::io::{self, stdout, Write as _}; | ||
| use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering}; | ||
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| static COLLECTOR: Collector = Collector::new(); | ||
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| /// Enables the collection of statistics. | ||
| /// To be effective it has to be called before the first use of a statistics. | ||
| pub fn try_enable() -> Result<(), ()> { | ||
| COLLECTOR.try_enable() | ||
| } | ||
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| /// Prints all statistics collected so far. | ||
| pub fn print() { | ||
| COLLECTOR.print(); | ||
| } | ||
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| pub struct Statistic { | ||
| category: &'static str, | ||
| name: &'static str, | ||
| initialized: AtomicBool, | ||
| value: AtomicUsize, | ||
| } | ||
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| struct Collector(Mutex<State>); | ||
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| struct State { | ||
| enabled: bool, | ||
| stats: Vec<&'static Statistic>, | ||
| } | ||
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| #[derive(Eq, PartialEq, Ord, PartialOrd)] | ||
| struct Snapshot { | ||
| category: &'static str, | ||
| name: &'static str, | ||
| value: usize, | ||
| } | ||
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| impl Statistic { | ||
| pub const fn new(category: &'static str, name: &'static str) -> Self { | ||
| Statistic { | ||
| category, | ||
| name, | ||
| initialized: AtomicBool::new(false), | ||
| value: AtomicUsize::new(0), | ||
| } | ||
| } | ||
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| pub fn name(&self) -> &'static str { | ||
| self.name | ||
| } | ||
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| pub fn category(&self) -> &'static str { | ||
| self.category.rsplit("::").next().unwrap() | ||
| } | ||
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| #[inline] | ||
| pub fn register(&'static self) { | ||
| if cfg!(debug_assertions) { | ||
| if !self.initialized.load(Ordering::Acquire) { | ||
| COLLECTOR.register(self); | ||
| } | ||
| } | ||
| } | ||
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| #[inline] | ||
| pub fn increment(&'static self, value: usize) { | ||
| if cfg!(debug_assertions) { | ||
| self.value.fetch_add(value, Ordering::Relaxed); | ||
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|
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| self.register(); | ||
| } | ||
| } | ||
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| #[inline] | ||
| pub fn update_max(&'static self, value: usize) { | ||
| if cfg!(debug_assertions) { | ||
| self.value.fetch_max(value, Ordering::Relaxed); | ||
| self.register(); | ||
| } | ||
| } | ||
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| fn snapshot(&'static self) -> Snapshot { | ||
| Snapshot { | ||
| name: self.name(), | ||
| category: self.category(), | ||
| value: self.value.load(Ordering::Relaxed), | ||
| } | ||
| } | ||
| } | ||
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| impl Collector { | ||
| const fn new() -> Self { | ||
| Collector(const_mutex(State { enabled: false, stats: Vec::new() })) | ||
| } | ||
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| fn try_enable(&self) -> Result<(), ()> { | ||
| if cfg!(debug_assertions) { | ||
| self.0.lock().enabled = true; | ||
| Ok(()) | ||
| } else { | ||
| Err(()) | ||
| } | ||
| } | ||
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| fn snapshot(&self) -> Vec<Snapshot> { | ||
| self.0.lock().stats.iter().copied().map(Statistic::snapshot).collect() | ||
| } | ||
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| fn register(&self, s: &'static Statistic) { | ||
| let mut state = self.0.lock(); | ||
| if !s.initialized.load(Ordering::Relaxed) { | ||
| if state.enabled { | ||
| state.stats.push(s); | ||
| } | ||
| s.initialized.store(true, Ordering::Release); | ||
| } | ||
| } | ||
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| fn print(&self) { | ||
| let mut stats = self.snapshot(); | ||
| stats.sort(); | ||
| match self.write(&stats) { | ||
| Ok(_) => {} | ||
| Err(e) if e.kind() == io::ErrorKind::BrokenPipe => {} | ||
| Err(e) => panic!(e), | ||
| } | ||
| } | ||
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| fn write(&self, stats: &[Snapshot]) -> io::Result<()> { | ||
| let mut cat_width = 0; | ||
| let mut val_width = 0; | ||
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| for s in stats { | ||
| cat_width = cat_width.max(s.category.len()); | ||
| val_width = val_width.max(s.value.to_string().len()); | ||
| } | ||
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| let mut out = Vec::new(); | ||
| for s in stats { | ||
| write!( | ||
| &mut out, | ||
| "{val:val_width$} {cat:cat_width$} {name}\n", | ||
| val = s.value, | ||
| val_width = val_width, | ||
| cat = s.category, | ||
| cat_width = cat_width, | ||
| name = s.name, | ||
| )?; | ||
| } | ||
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| stdout().write_all(&out) | ||
| } | ||
| } | ||
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This should be part of
SessionorTyCtxt. There may be multiple rustc sessions running in a single process. (for example when using RLS)There was a problem hiding this comment.
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I experimented with different implementation approaches:
I strongly prefer variants that put statistics definitions together with MIR passes that uses them. In that approach, adding and removing counters is trivial, additionally any unused counters are detected as such during compilation.
Values can be stored in the context if we want to support multiple rustc sessions in a single process, although it requires passing context to all those places where counters are used. But is there any real use-case? Why would you use rustc with debug-assertions and MIR optimizations counters inside the RLS?
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I agree with @bjorn3. We've tried pretty hard to move these sorts of things into
SessionandTyCtxtto allow running multiple sessions in the same process (both for RLS and eventually for one rustc process compiling multiple crates simultaneously).Since this is essentially unstable, diagnostic data and doesn't effect the compilation artifacts, it may be worth bending that rule because, as you point out, having the counters defined in their MIR passes is quite nice. I don't personally feel comfortable approving that since this is a cross-cutting concern for the compiler as a whole and there may be others on the compiler team that have strong opinions about breaking that rule.