./miri bench: add a flag to skip the install step

ci/ci.sh

@@ -18,7 +18,7 @@ export RUSTFLAGS="-D warnings"
 export CARGO_INCREMENTAL=0
 export CARGO_EXTRA_FLAGS="--locked"
 
-# Determine configuration for installed build (used by test-cargo-miri).
+# Determine configuration for installed build (used by test-cargo-miri and `./miri bench`).
 echo "Installing release version of Miri"
 time ./miri install
 
@@ -73,7 +73,7 @@ function run_tests {
   fi
   if [ -n "${TEST_BENCH-}" ]; then
     # Check that the benchmarks build and run, but only once.
-    time HYPERFINE="hyperfine -w0 -r1 --show-output" ./miri bench $TARGET_FLAG
+    time HYPERFINE="hyperfine -w0 -r1 --show-output" ./miri bench $TARGET_FLAG --no-install
   fi
   # Smoke-test `./miri run --dep`.
   ./miri run $TARGET_FLAG --dep tests/pass-dep/getrandom.rs

miri-script/src/commands.rs

@@ -179,7 +179,8 @@ impl Command {
             Command::Doc { flags } => Self::doc(flags),
             Command::Fmt { flags } => Self::fmt(flags),
             Command::Clippy { flags } => Self::clippy(flags),
-            Command::Bench { target, benches } => Self::bench(target, benches),
+            Command::Bench { target, no_install, benches } =>
+                Self::bench(target, no_install, benches),
             Command::Toolchain { flags } => Self::toolchain(flags),
             Command::RustcPull { commit } => Self::rustc_pull(commit.clone()),
             Command::RustcPush { github_user, branch } => Self::rustc_push(github_user, branch),
@@ -378,16 +379,18 @@ impl Command {
         Ok(())
     }
 
-    fn bench(target: Option<String>, benches: Vec<String>) -> Result<()> {
+    fn bench(target: Option<String>, no_install: bool, benches: Vec<String>) -> Result<()> {
         // The hyperfine to use
         let hyperfine = env::var("HYPERFINE");
         let hyperfine = hyperfine.as_deref().unwrap_or("hyperfine -w 1 -m 5 --shell=none");
         let hyperfine = shell_words::split(hyperfine)?;
         let Some((program_name, args)) = hyperfine.split_first() else {
             bail!("expected HYPERFINE environment variable to be non-empty");
         };
-        // Make sure we have an up-to-date Miri installed and selected the right toolchain.
-        Self::install(vec![])?;
+        if !no_install {
+            // Make sure we have an up-to-date Miri installed and selected the right toolchain.
+            Self::install(vec![])?;
+        }
 
         let sh = Shell::new()?;
         sh.change_dir(miri_dir()?);

miri-script/src/main.rs

@@ -69,6 +69,8 @@ pub enum Command {
     /// Runs the benchmarks from bench-cargo-miri in hyperfine. hyperfine needs to be installed.
     Bench {
         target: Option<String>,
+        /// When `true`, skip the `./miri install` step.
+        no_install: bool,
         /// List of benchmarks to run. By default all benchmarks are run.
         benches: Vec<String>,
     },
@@ -121,9 +123,11 @@ install`. Sets up the rpath such that the installed binary should work in any
 working directory. Note that the binaries are placed in the `miri` toolchain
 sysroot, to prevent conflicts with other toolchains.
 
-./miri bench [--target <target>] <benches>:
+./miri bench [--target <target>] [--no-install] <benches>:
 Runs the benchmarks from bench-cargo-miri in hyperfine. hyperfine needs to be installed.
 <benches> can explicitly list the benchmarks to run; by default, all of them are run.
+By default, this runs `./miri install` to ensure the latest local Miri is being benchmarked;
+`--no-install` can be used to skip that step.
 
 ./miri toolchain <flags>:
 Update and activate the rustup toolchain 'miri' to the commit given in the
@@ -218,16 +222,19 @@ fn main() -> Result<()> {
         Some("bench") => {
             let mut target = None;
             let mut benches = Vec::new();
+            let mut no_install = false;
             loop {
                 if let Some(val) = args.get_long_opt("target")? {
                     target = Some(val);
+                } else if args.get_long_flag("no-install")? {
+                    no_install = true;
                 } else if let Some(flag) = args.get_other() {
                     benches.push(flag);
                 } else {
                     break;
                 }
             }
-            Command::Bench { target, benches }
+            Command::Bench { target, benches, no_install }
         }
         Some("toolchain") => Command::Toolchain { flags: args.remainder() },
         Some("rustc-pull") => {