Auto merge of rust-lang#2699 - RalfJung:schedule-refactor, r=RalfJung

refactor scheduler

Refactors the scheduler to use something akin to a generator -- a callback that will be invoked when the stack of a thread is empty, which has the chance to push a new stack frame or do other things and then indicates whether this thread is done, or should be scheduled again. (Unfortunately I think we [cannot use actual generators](https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/Generators.20that.20borrow.20on.20each.20resume.3F) here.) The interpreter loop is now a proper infinite loop, the only way to leave it is for some kind of interrupt to be triggered (represented as `InterpError`) -- unifying how we handle 'exit when calling `process::exit`' and 'exit when main thread quits'.

The last commit implements an alternative approach to rust-lang/miri#2660 using this new structure. Fixes rust-lang/miri#2629.

Author: bors

src/tools/miri/cargo-miri/src/setup.rs

@@ -99,12 +99,10 @@ pub fn setup(subcommand: &MiriCommand, target: &str, rustc_version: &VersionMeta
         // `config.toml`.
         command.env("RUSTC_WRAPPER", "");
 
-        if only_setup {
-            if print_sysroot {
-                // Be extra sure there is no noise on stdout.
-                command.stdout(process::Stdio::null());
-            }
+        if only_setup && !print_sysroot {
+            // Forward output.
         } else {
+            // Supress output.
             command.stdout(process::Stdio::null());
             command.stderr(process::Stdio::null());
         }
@@ -120,7 +118,9 @@ pub fn setup(subcommand: &MiriCommand, target: &str, rustc_version: &VersionMeta
     std::env::set_var("MIRI_SYSROOT", &sysroot_dir);
 
     // Do the build.
-    if only_setup {
+    if print_sysroot {
+        // Be silent.
+    } else if only_setup {
         // We want to be explicit.
         eprintln!("Preparing a sysroot for Miri (target: {target})...");
     } else {
@@ -143,7 +143,9 @@ pub fn setup(subcommand: &MiriCommand, target: &str, rustc_version: &VersionMeta
                 )
             }
         });
-    if only_setup {
+    if print_sysroot {
+        // Be silent.
+    } else if only_setup {
         eprintln!("A sysroot for Miri is now available in `{}`.", sysroot_dir.display());
     } else {
         eprintln!("done");

src/tools/miri/ci.sh

@@ -40,10 +40,15 @@ function run_tests {
   ./miri test
   if [ -z "${MIRI_TEST_TARGET+exists}" ]; then
     # Only for host architecture: tests with optimizations (`-O` is what cargo passes, but crank MIR
-    # optimizations up all the way).
-    # Optimizations change diagnostics (mostly backtraces), so we don't check them
-    #FIXME(#2155): we want to only run the pass and panic tests here, not the fail tests.
+    # optimizations up all the way, too).
+    # Optimizations change diagnostics (mostly backtraces), so we don't check
+    # them. Also error locations change so we don't run the failing tests.
     MIRIFLAGS="${MIRIFLAGS:-} -O -Zmir-opt-level=4" MIRI_SKIP_UI_CHECKS=1 ./miri test -- tests/{pass,panic}
+
+    # Also run some many-seeds tests. 64 seeds means this takes around a minute per test.
+    for FILE in tests/many-seeds/*.rs; do
+      MIRI_SEEDS=64 CARGO_EXTRA_FLAGS="$CARGO_EXTRA_FLAGS -q" ./miri many-seeds ./miri run "$FILE"
+    done
   fi
 
   ## test-cargo-miri

src/tools/miri/miri

@@ -36,7 +36,8 @@ Mainly meant to be invoked by rust-analyzer.
 ./miri many-seeds <command>:
 Runs <command> over and over again with different seeds for Miri. The MIRIFLAGS
 variable is set to its original value appended with ` -Zmiri-seed=$SEED` for
-many different seeds.
+many different seeds. The MIRI_SEEDS variable controls how many seeds are being
+tried; MIRI_SEED_START controls the first seed to try.
 
 ./miri bench <benches>:
 Runs the benchmarks from bench-cargo-miri in hyperfine. hyperfine needs to be installed.
@@ -174,7 +175,9 @@ rustc-push)
     fi
     ;;
 many-seeds)
-    for SEED in $(seq 0 255); do
+    MIRI_SEED_START=${MIRI_SEED_START:-0} # default to 0
+    MIRI_SEEDS=${MIRI_SEEDS:-256} # default to 256
+    for SEED in $(seq $MIRI_SEED_START $(( $MIRI_SEED_START + $MIRI_SEEDS - 1 )) ); do
         echo "Trying seed: $SEED"
         MIRIFLAGS="$MIRIFLAGS -Zlayout-seed=$SEED -Zmiri-seed=$SEED" $@ || { echo "Failing seed: $SEED"; break; }
     done
@@ -249,6 +252,8 @@ export RUSTFLAGS="-C link-args=-Wl,-rpath,$LIBDIR $RUSTFLAGS"
 # Build a sysroot and set MIRI_SYSROOT to use it. Arguments are passed to `cargo miri setup`.
 build_sysroot() {
     if ! MIRI_SYSROOT="$($CARGO run $CARGO_EXTRA_FLAGS --manifest-path "$MIRIDIR"/cargo-miri/Cargo.toml -- miri setup --print-sysroot "$@")"; then
+        # Run it again so the user can see the error.
+        $CARGO run $CARGO_EXTRA_FLAGS --manifest-path "$MIRIDIR"/cargo-miri/Cargo.toml -- miri setup "$@"
         echo "'cargo miri setup' failed"
         exit 1
     fi