diff --git a/compiler/rustc_trait_selection/src/traits/vtable.rs b/compiler/rustc_trait_selection/src/traits/vtable.rs
index 6e6f948a2cdc4..ed221e2a1835f 100644
--- a/compiler/rustc_trait_selection/src/traits/vtable.rs
+++ b/compiler/rustc_trait_selection/src/traits/vtable.rs
@@ -154,18 +154,17 @@ fn prepare_vtable_segments_inner<'tcx, T>(
 
         // emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
         while let Some((inner_most_trait_ref, emit_vptr, mut siblings)) = stack.pop() {
+            let has_entries =
+                has_own_existential_vtable_entries(tcx, inner_most_trait_ref.def_id());
+
             segment_visitor(VtblSegment::TraitOwnEntries {
                 trait_ref: inner_most_trait_ref,
-                emit_vptr: emit_vptr && !tcx.sess.opts.unstable_opts.no_trait_vptr,
+                emit_vptr: emit_vptr && has_entries && !tcx.sess.opts.unstable_opts.no_trait_vptr,
             })?;
 
             // If we've emitted (fed to `segment_visitor`) a trait that has methods present in the vtable,
             // we'll need to emit vptrs from now on.
-            if !emit_vptr_on_new_entry
-                && has_own_existential_vtable_entries(tcx, inner_most_trait_ref.def_id())
-            {
-                emit_vptr_on_new_entry = true;
-            }
+            emit_vptr_on_new_entry |= has_entries;
 
             if let Some(next_inner_most_trait_ref) =
                 siblings.find(|&sibling| visited.insert(sibling.upcast(tcx)))
diff --git a/library/std/src/sys/pal/unix/stack_overflow.rs b/library/std/src/sys/pal/unix/stack_overflow.rs
index ac0858e1de876..69b31da427fcb 100644
--- a/library/std/src/sys/pal/unix/stack_overflow.rs
+++ b/library/std/src/sys/pal/unix/stack_overflow.rs
@@ -265,9 +265,7 @@ mod imp {
     /// Modern kernels on modern hardware can have dynamic signal stack sizes.
     #[cfg(any(target_os = "linux", target_os = "android"))]
     fn sigstack_size() -> usize {
-        // FIXME: reuse const from libc when available?
-        const AT_MINSIGSTKSZ: crate::ffi::c_ulong = 51;
-        let dynamic_sigstksz = unsafe { libc::getauxval(AT_MINSIGSTKSZ) };
+        let dynamic_sigstksz = unsafe { libc::getauxval(libc::AT_MINSIGSTKSZ) };
         // If getauxval couldn't find the entry, it returns 0,
         // so take the higher of the "constant" and auxval.
         // This transparently supports older kernels which don't provide AT_MINSIGSTKSZ
diff --git a/src/tools/compiletest/src/lib.rs b/src/tools/compiletest/src/lib.rs
index 2e66c084dd75e..d045c6fe05312 100644
--- a/src/tools/compiletest/src/lib.rs
+++ b/src/tools/compiletest/src/lib.rs
@@ -464,9 +464,7 @@ pub fn run_tests(config: Arc<Config>) {
     // structure for each test (or each revision of a multi-revision test).
     let mut tests = Vec::new();
     for c in configs {
-        let mut found_paths = HashSet::new();
-        make_tests(c, &mut tests, &mut found_paths);
-        check_overlapping_tests(&found_paths);
+        tests.extend(collect_and_make_tests(c));
     }
 
     tests.sort_by(|a, b| a.desc.name.as_slice().cmp(&b.desc.name.as_slice()));
@@ -545,46 +543,62 @@ pub fn test_opts(config: &Config) -> test::TestOpts {
     }
 }
 
+/// Read-only context data used during test collection.
+struct TestCollectorCx {
+    config: Arc<Config>,
+    cache: HeadersCache,
+    common_inputs_stamp: Stamp,
+    modified_tests: Vec<PathBuf>,
+}
+
+/// Mutable state used during test collection.
+struct TestCollector {
+    tests: Vec<test::TestDescAndFn>,
+    found_path_stems: HashSet<PathBuf>,
+    poisoned: bool,
+}
+
 /// Creates libtest structures for every test/revision in the test suite directory.
 ///
 /// This always inspects _all_ test files in the suite (e.g. all 17k+ ui tests),
 /// regardless of whether any filters/tests were specified on the command-line,
 /// because filtering is handled later by libtest.
-pub fn make_tests(
-    config: Arc<Config>,
-    tests: &mut Vec<test::TestDescAndFn>,
-    found_paths: &mut HashSet<PathBuf>,
-) {
+pub fn collect_and_make_tests(config: Arc<Config>) -> Vec<test::TestDescAndFn> {
     debug!("making tests from {:?}", config.src_base.display());
-    let inputs = common_inputs_stamp(&config);
+    let common_inputs_stamp = common_inputs_stamp(&config);
     let modified_tests = modified_tests(&config, &config.src_base).unwrap_or_else(|err| {
         panic!("modified_tests got error from dir: {}, error: {}", config.src_base.display(), err)
     });
-
     let cache = HeadersCache::load(&config);
-    let mut poisoned = false;
-    collect_tests_from_dir(
-        config.clone(),
-        &cache,
-        &config.src_base,
-        &PathBuf::new(),
-        &inputs,
-        tests,
-        found_paths,
-        &modified_tests,
-        &mut poisoned,
-    )
-    .unwrap_or_else(|reason| {
-        panic!("Could not read tests from {}: {reason}", config.src_base.display())
-    });
+
+    let cx = TestCollectorCx { config, cache, common_inputs_stamp, modified_tests };
+    let mut collector =
+        TestCollector { tests: vec![], found_path_stems: HashSet::new(), poisoned: false };
+
+    collect_tests_from_dir(&cx, &mut collector, &cx.config.src_base, &PathBuf::new())
+        .unwrap_or_else(|reason| {
+            panic!("Could not read tests from {}: {reason}", cx.config.src_base.display())
+        });
+
+    let TestCollector { tests, found_path_stems, poisoned } = collector;
 
     if poisoned {
         eprintln!();
         panic!("there are errors in tests");
     }
+
+    check_for_overlapping_test_paths(&found_path_stems);
+
+    tests
 }
 
-/// Returns a stamp constructed from input files common to all test cases.
+/// Returns the most recent last-modified timestamp from among the input files
+/// that are considered relevant to all tests (e.g. the compiler, std, and
+/// compiletest itself).
+///
+/// (Some of these inputs aren't actually relevant to _all_ tests, but they are
+/// common to some subset of tests, and are hopefully unlikely to be modified
+/// while working on other tests.)
 fn common_inputs_stamp(config: &Config) -> Stamp {
     let rust_src_dir = config.find_rust_src_root().expect("Could not find Rust source root");
 
@@ -662,15 +676,10 @@ fn modified_tests(config: &Config, dir: &Path) -> Result<Vec<PathBuf>, String> {
 /// Recursively scans a directory to find test files and create test structures
 /// that will be handed over to libtest.
 fn collect_tests_from_dir(
-    config: Arc<Config>,
-    cache: &HeadersCache,
+    cx: &TestCollectorCx,
+    collector: &mut TestCollector,
     dir: &Path,
     relative_dir_path: &Path,
-    inputs: &Stamp,
-    tests: &mut Vec<test::TestDescAndFn>,
-    found_paths: &mut HashSet<PathBuf>,
-    modified_tests: &Vec<PathBuf>,
-    poisoned: &mut bool,
 ) -> io::Result<()> {
     // Ignore directories that contain a file named `compiletest-ignore-dir`.
     if dir.join("compiletest-ignore-dir").exists() {
@@ -679,7 +688,7 @@ fn collect_tests_from_dir(
 
     // For run-make tests, a "test file" is actually a directory that contains
     // an `rmake.rs` or `Makefile`"
-    if config.mode == Mode::RunMake {
+    if cx.config.mode == Mode::RunMake {
         if dir.join("Makefile").exists() && dir.join("rmake.rs").exists() {
             return Err(io::Error::other(
                 "run-make tests cannot have both `Makefile` and `rmake.rs`",
@@ -691,7 +700,7 @@ fn collect_tests_from_dir(
                 file: dir.to_path_buf(),
                 relative_dir: relative_dir_path.parent().unwrap().to_path_buf(),
             };
-            tests.extend(make_test(config, cache, &paths, inputs, poisoned));
+            make_test(cx, collector, &paths);
             // This directory is a test, so don't try to find other tests inside it.
             return Ok(());
         }
@@ -703,7 +712,7 @@ fn collect_tests_from_dir(
     // sequential loop because otherwise, if we do it in the
     // tests themselves, they race for the privilege of
     // creating the directories and sometimes fail randomly.
-    let build_dir = output_relative_path(&config, relative_dir_path);
+    let build_dir = output_relative_path(&cx.config, relative_dir_path);
     fs::create_dir_all(&build_dir).unwrap();
 
     // Add each `.rs` file as a test, and recurse further on any
@@ -715,33 +724,25 @@ fn collect_tests_from_dir(
         let file_path = file.path();
         let file_name = file.file_name();
 
-        if is_test(&file_name) && (!config.only_modified || modified_tests.contains(&file_path)) {
+        if is_test(&file_name)
+            && (!cx.config.only_modified || cx.modified_tests.contains(&file_path))
+        {
             // We found a test file, so create the corresponding libtest structures.
             debug!("found test file: {:?}", file_path.display());
 
             // Record the stem of the test file, to check for overlaps later.
             let rel_test_path = relative_dir_path.join(file_path.file_stem().unwrap());
-            found_paths.insert(rel_test_path);
+            collector.found_path_stems.insert(rel_test_path);
 
             let paths =
                 TestPaths { file: file_path, relative_dir: relative_dir_path.to_path_buf() };
-            tests.extend(make_test(config.clone(), cache, &paths, inputs, poisoned))
+            make_test(cx, collector, &paths);
         } else if file_path.is_dir() {
             // Recurse to find more tests in a subdirectory.
             let relative_file_path = relative_dir_path.join(file.file_name());
             if &file_name != "auxiliary" {
                 debug!("found directory: {:?}", file_path.display());
-                collect_tests_from_dir(
-                    config.clone(),
-                    cache,
-                    &file_path,
-                    &relative_file_path,
-                    inputs,
-                    tests,
-                    found_paths,
-                    modified_tests,
-                    poisoned,
-                )?;
+                collect_tests_from_dir(cx, collector, &file_path, &relative_file_path)?;
             }
         } else {
             debug!("found other file/directory: {:?}", file_path.display());
@@ -765,17 +766,11 @@ pub fn is_test(file_name: &OsString) -> bool {
 
 /// For a single test file, creates one or more test structures (one per revision)
 /// that can be handed over to libtest to run, possibly in parallel.
-fn make_test(
-    config: Arc<Config>,
-    cache: &HeadersCache,
-    testpaths: &TestPaths,
-    inputs: &Stamp,
-    poisoned: &mut bool,
-) -> Vec<test::TestDescAndFn> {
+fn make_test(cx: &TestCollectorCx, collector: &mut TestCollector, testpaths: &TestPaths) {
     // For run-make tests, each "test file" is actually a _directory_ containing
     // an `rmake.rs` or `Makefile`. But for the purposes of directive parsing,
     // we want to look at that recipe file, not the directory itself.
-    let test_path = if config.mode == Mode::RunMake {
+    let test_path = if cx.config.mode == Mode::RunMake {
         if testpaths.file.join("rmake.rs").exists() && testpaths.file.join("Makefile").exists() {
             panic!("run-make tests cannot have both `rmake.rs` and `Makefile`");
         }
@@ -792,7 +787,7 @@ fn make_test(
     };
 
     // Scan the test file to discover its revisions, if any.
-    let early_props = EarlyProps::from_file(&config, &test_path);
+    let early_props = EarlyProps::from_file(&cx.config, &test_path);
 
     // Normally we create one libtest structure per revision, with two exceptions:
     // - If a test doesn't use revisions, create a dummy revision (None) so that
@@ -800,49 +795,49 @@ fn make_test(
     // - Incremental tests inherently can't run their revisions in parallel, so
     //   we treat them like non-revisioned tests here. Incremental revisions are
     //   handled internally by `runtest::run` instead.
-    let revisions = if early_props.revisions.is_empty() || config.mode == Mode::Incremental {
+    let revisions = if early_props.revisions.is_empty() || cx.config.mode == Mode::Incremental {
         vec![None]
     } else {
         early_props.revisions.iter().map(|r| Some(r.as_str())).collect()
     };
 
-    // For each revision (or the sole dummy revision), create and return a
+    // For each revision (or the sole dummy revision), create and append a
     // `test::TestDescAndFn` that can be handed over to libtest.
-    revisions
-        .into_iter()
-        .map(|revision| {
-            // Create a test name and description to hand over to libtest.
-            let src_file =
-                std::fs::File::open(&test_path).expect("open test file to parse ignores");
-            let test_name = crate::make_test_name(&config, testpaths, revision);
-            // Create a libtest description for the test/revision.
-            // This is where `ignore-*`/`only-*`/`needs-*` directives are handled,
-            // because they need to set the libtest ignored flag.
-            let mut desc = make_test_description(
-                &config, cache, test_name, &test_path, src_file, revision, poisoned,
-            );
+    collector.tests.extend(revisions.into_iter().map(|revision| {
+        // Create a test name and description to hand over to libtest.
+        let src_file = fs::File::open(&test_path).expect("open test file to parse ignores");
+        let test_name = make_test_name(&cx.config, testpaths, revision);
+        // Create a libtest description for the test/revision.
+        // This is where `ignore-*`/`only-*`/`needs-*` directives are handled,
+        // because they need to set the libtest ignored flag.
+        let mut desc = make_test_description(
+            &cx.config,
+            &cx.cache,
+            test_name,
+            &test_path,
+            src_file,
+            revision,
+            &mut collector.poisoned,
+        );
 
-            // If a test's inputs haven't changed since the last time it ran,
-            // mark it as ignored so that libtest will skip it.
-            if !config.force_rerun
-                && is_up_to_date(&config, testpaths, &early_props, revision, inputs)
-            {
-                desc.ignore = true;
-                // Keep this in sync with the "up-to-date" message detected by bootstrap.
-                desc.ignore_message = Some("up-to-date");
-            }
+        // If a test's inputs haven't changed since the last time it ran,
+        // mark it as ignored so that libtest will skip it.
+        if !cx.config.force_rerun && is_up_to_date(cx, testpaths, &early_props, revision) {
+            desc.ignore = true;
+            // Keep this in sync with the "up-to-date" message detected by bootstrap.
+            desc.ignore_message = Some("up-to-date");
+        }
 
-            // Create the callback that will run this test/revision when libtest calls it.
-            let testfn = make_test_closure(config.clone(), testpaths, revision);
+        // Create the callback that will run this test/revision when libtest calls it.
+        let testfn = make_test_closure(Arc::clone(&cx.config), testpaths, revision);
 
-            test::TestDescAndFn { desc, testfn }
-        })
-        .collect()
+        test::TestDescAndFn { desc, testfn }
+    }));
 }
 
 /// The path of the `stamp` file that gets created or updated whenever a
 /// particular test completes successfully.
-fn stamp(config: &Config, testpaths: &TestPaths, revision: Option<&str>) -> PathBuf {
+fn stamp_file_path(config: &Config, testpaths: &TestPaths, revision: Option<&str>) -> PathBuf {
     output_base_dir(config, testpaths, revision).join("stamp")
 }
 
@@ -891,21 +886,20 @@ fn files_related_to_test(
 /// (This is not very reliable in some circumstances, so the `--force-rerun`
 /// flag can be used to ignore up-to-date checking and always re-run tests.)
 fn is_up_to_date(
-    config: &Config,
+    cx: &TestCollectorCx,
     testpaths: &TestPaths,
     props: &EarlyProps,
     revision: Option<&str>,
-    inputs: &Stamp, // Last-modified timestamp of the compiler, compiletest etc
 ) -> bool {
-    let stamp_name = stamp(config, testpaths, revision);
+    let stamp_file_path = stamp_file_path(&cx.config, testpaths, revision);
     // Check the config hash inside the stamp file.
-    let contents = match fs::read_to_string(&stamp_name) {
+    let contents = match fs::read_to_string(&stamp_file_path) {
         Ok(f) => f,
         Err(ref e) if e.kind() == ErrorKind::InvalidData => panic!("Can't read stamp contents"),
         // The test hasn't succeeded yet, so it is not up-to-date.
         Err(_) => return false,
     };
-    let expected_hash = runtest::compute_stamp_hash(config);
+    let expected_hash = runtest::compute_stamp_hash(&cx.config);
     if contents != expected_hash {
         // Some part of compiletest configuration has changed since the test
         // last succeeded, so it is not up-to-date.
@@ -914,14 +908,14 @@ fn is_up_to_date(
 
     // Check the timestamp of the stamp file against the last modified time
     // of all files known to be relevant to the test.
-    let mut inputs = inputs.clone();
-    for path in files_related_to_test(config, testpaths, props, revision) {
-        inputs.add_path(&path);
+    let mut inputs_stamp = cx.common_inputs_stamp.clone();
+    for path in files_related_to_test(&cx.config, testpaths, props, revision) {
+        inputs_stamp.add_path(&path);
     }
 
     // If no relevant files have been modified since the stamp file was last
     // written, the test is up-to-date.
-    inputs < Stamp::from_path(&stamp_name)
+    inputs_stamp < Stamp::from_path(&stamp_file_path)
 }
 
 /// The maximum of a set of file-modified timestamps.
@@ -1029,11 +1023,11 @@ fn make_test_closure(
 /// To avoid problems, we forbid test names from overlapping in this way.
 ///
 /// See <https://github.com/rust-lang/rust/pull/109509> for more context.
-fn check_overlapping_tests(found_paths: &HashSet<PathBuf>) {
+fn check_for_overlapping_test_paths(found_path_stems: &HashSet<PathBuf>) {
     let mut collisions = Vec::new();
-    for path in found_paths {
+    for path in found_path_stems {
         for ancestor in path.ancestors().skip(1) {
-            if found_paths.contains(ancestor) {
+            if found_path_stems.contains(ancestor) {
                 collisions.push((path, ancestor));
             }
         }
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 69a47fcd0fbea..f0452008304b4 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -29,7 +29,7 @@ use crate::errors::{self, Error, ErrorKind};
 use crate::header::TestProps;
 use crate::read2::{Truncated, read2_abbreviated};
 use crate::util::{PathBufExt, add_dylib_path, logv, static_regex};
-use crate::{ColorConfig, json};
+use crate::{ColorConfig, json, stamp_file_path};
 
 mod debugger;
 
@@ -2595,8 +2595,8 @@ impl<'test> TestCx<'test> {
     }
 
     fn create_stamp(&self) {
-        let stamp = crate::stamp(&self.config, self.testpaths, self.revision);
-        fs::write(&stamp, compute_stamp_hash(&self.config)).unwrap();
+        let stamp_file_path = stamp_file_path(&self.config, self.testpaths, self.revision);
+        fs::write(&stamp_file_path, compute_stamp_hash(&self.config)).unwrap();
     }
 
     fn init_incremental_test(&self) {
diff --git a/tests/ui/traits/object/print_vtable_sizes.stdout b/tests/ui/traits/object/print_vtable_sizes.stdout
index b43e168df3f38..4daf476957657 100644
--- a/tests/ui/traits/object/print_vtable_sizes.stdout
+++ b/tests/ui/traits/object/print_vtable_sizes.stdout
@@ -1,8 +1,8 @@
-print-vtable-sizes { "crate_name": "print_vtable_sizes", "trait_name": "E", "entries": "6", "entries_ignoring_upcasting": "4", "entries_for_upcasting": "2", "upcasting_cost_percent": "50" }
-print-vtable-sizes { "crate_name": "print_vtable_sizes", "trait_name": "G", "entries": "14", "entries_ignoring_upcasting": "11", "entries_for_upcasting": "3", "upcasting_cost_percent": "27.27272727272727" }
 print-vtable-sizes { "crate_name": "print_vtable_sizes", "trait_name": "A", "entries": "6", "entries_ignoring_upcasting": "5", "entries_for_upcasting": "1", "upcasting_cost_percent": "20" }
+print-vtable-sizes { "crate_name": "print_vtable_sizes", "trait_name": "G", "entries": "13", "entries_ignoring_upcasting": "11", "entries_for_upcasting": "2", "upcasting_cost_percent": "18.181818181818183" }
 print-vtable-sizes { "crate_name": "print_vtable_sizes", "trait_name": "B", "entries": "4", "entries_ignoring_upcasting": "4", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
 print-vtable-sizes { "crate_name": "print_vtable_sizes", "trait_name": "D", "entries": "4", "entries_ignoring_upcasting": "4", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
+print-vtable-sizes { "crate_name": "print_vtable_sizes", "trait_name": "E", "entries": "4", "entries_ignoring_upcasting": "4", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
 print-vtable-sizes { "crate_name": "print_vtable_sizes", "trait_name": "F", "entries": "6", "entries_ignoring_upcasting": "6", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
 print-vtable-sizes { "crate_name": "print_vtable_sizes", "trait_name": "_::S", "entries": "3", "entries_ignoring_upcasting": "3", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
 print-vtable-sizes { "crate_name": "print_vtable_sizes", "trait_name": "_::S", "entries": "3", "entries_ignoring_upcasting": "3", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
diff --git a/tests/ui/traits/upcast_reorder.rs b/tests/ui/traits/upcast_reorder.rs
new file mode 100644
index 0000000000000..55e6ad4c368d1
--- /dev/null
+++ b/tests/ui/traits/upcast_reorder.rs
@@ -0,0 +1,29 @@
+//@ run-pass
+//
+// issue: <https://github.com/rust-lang/rust/issues/131813>
+
+#![feature(trait_upcasting)]
+
+trait Pollable {
+    #[allow(unused)]
+    fn poll(&self) {}
+}
+trait FileIo: Pollable + Send + Sync {
+    fn read(&self) {}
+}
+trait Terminal: Send + Sync + FileIo {}
+
+struct A;
+
+impl Pollable for A {}
+impl FileIo for A {}
+impl Terminal for A {}
+
+fn main() {
+    let a = A;
+
+    let b = &a as &dyn Terminal;
+    let c = b as &dyn FileIo;
+
+    c.read();
+}
diff --git a/tests/ui/traits/vtable/multiple-markers.stderr b/tests/ui/traits/vtable/multiple-markers.stderr
index 4497c703ae8a1..36ac8b24eb530 100644
--- a/tests/ui/traits/vtable/multiple-markers.stderr
+++ b/tests/ui/traits/vtable/multiple-markers.stderr
@@ -14,7 +14,6 @@ error: vtable entries for `<S as B>`: [
            MetadataSize,
            MetadataAlign,
            Method(<S as T>::method),
-           TraitVPtr(<S as M2>),
        ]
   --> $DIR/multiple-markers.rs:24:1
    |
@@ -26,8 +25,6 @@ error: vtable entries for `<S as C>`: [
            MetadataSize,
            MetadataAlign,
            Method(<S as T>::method),
-           TraitVPtr(<S as M1>),
-           TraitVPtr(<S as M2>),
        ]
   --> $DIR/multiple-markers.rs:27:1
    |
@@ -39,9 +36,6 @@ error: vtable entries for `<S as D>`: [
            MetadataSize,
            MetadataAlign,
            Method(<S as T>::method),
-           TraitVPtr(<S as M0>),
-           TraitVPtr(<S as M1>),
-           TraitVPtr(<S as M2>),
        ]
   --> $DIR/multiple-markers.rs:30:1
    |