ci: Print out how long each step takes on CI

This commit updates CI configuration to inform rustbuild that it should print
out how long each step takes on CI. This'll hopefully allow us to track the
duration of steps over time and follow regressions a bit more closesly (as well
as have closer analysis of differences between two builds).

cc #48829

src/bootstrap/builder.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 use std::any::Any;
-use std::cell::RefCell;
+use std::cell::{Cell, RefCell};
 use std::collections::BTreeSet;
 use std::env;
 use std::fmt::Debug;
@@ -18,6 +18,7 @@ use std::hash::Hash;
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
 use std::process::Command;
+use std::time::{Instant, Duration};
 
 use compile;
 use install;
@@ -40,6 +41,7 @@ pub struct Builder<'a> {
     pub kind: Kind,
     cache: Cache,
     stack: RefCell<Vec<Box<Any>>>,
+    time_spent_on_dependencies: Cell<Duration>,
 }
 
 impl<'a> Deref for Builder<'a> {
@@ -343,6 +345,7 @@ impl<'a> Builder<'a> {
             kind,
             cache: Cache::new(),
             stack: RefCell::new(Vec::new()),
+            time_spent_on_dependencies: Cell::new(Duration::new(0, 0)),
         };
 
         let builder = &builder;
@@ -383,6 +386,7 @@ impl<'a> Builder<'a> {
             kind,
             cache: Cache::new(),
             stack: RefCell::new(Vec::new()),
+            time_spent_on_dependencies: Cell::new(Duration::new(0, 0)),
         };
 
         if kind == Kind::Dist {
@@ -662,6 +666,10 @@ impl<'a> Builder<'a> {
             cargo.env("RUSTC_ON_FAIL", on_fail);
         }
 
+        if self.config.print_step_timings {
+            cargo.env("RUSTC_PRINT_STEP_TIMINGS", "1");
+        }
+
         cargo.env("RUSTC_VERBOSE", format!("{}", self.verbosity));
 
         // Throughout the build Cargo can execute a number of build scripts
@@ -818,7 +826,24 @@ impl<'a> Builder<'a> {
             self.build.verbose(&format!("{}> {:?}", "  ".repeat(stack.len()), step));
             stack.push(Box::new(step.clone()));
         }
-        let out = step.clone().run(self);
+
+        let (out, dur) = {
+            let start = Instant::now();
+            let zero = Duration::new(0, 0);
+            let parent = self.time_spent_on_dependencies.replace(zero);
+            let out = step.clone().run(self);
+            let dur = start.elapsed();
+            let deps = self.time_spent_on_dependencies.replace(parent + dur);
+            (out, dur - deps)
+        };
+
+        if self.build.config.print_step_timings && dur > Duration::from_millis(100) {
+            println!("[TIMING] {:?} -- {}.{:03}",
+                     step,
+                     dur.as_secs(),
+                     dur.subsec_nanos() / 1_000_000);
+        }
+
         {
             let mut stack = self.stack.borrow_mut();
             let cur_step = stack.pop().expect("step stack empty");