diff --git a/src/tools/miri/.github/workflows/ci.yml b/src/tools/miri/.github/workflows/ci.yml
index 2c5868d5b37a..c5979e18a3b5 100644
--- a/src/tools/miri/.github/workflows/ci.yml
+++ b/src/tools/miri/.github/workflows/ci.yml
@@ -130,6 +130,10 @@ jobs:
         run: ./miri fmt --check
       - name: clippy
         run: ./miri clippy -- -D warnings
+      - name: clippy (no features)
+        run: ./miri clippy --no-default-features -- -D warnings
+      - name: clippy (all features)
+        run: ./miri clippy --all-features -- -D warnings
       - name: rustdoc
         run: RUSTDOCFLAGS="-Dwarnings" ./miri cargo doc --document-private-items
 
diff --git a/src/tools/miri/ci/ci.sh b/src/tools/miri/ci/ci.sh
index cccf10a7d703..32b58547d7c2 100755
--- a/src/tools/miri/ci/ci.sh
+++ b/src/tools/miri/ci/ci.sh
@@ -27,60 +27,59 @@ export RUSTFLAGS="-D warnings"
 export CARGO_INCREMENTAL=0
 export CARGO_EXTRA_FLAGS="--locked"
 
-# Determine configuration for installed build
+# Determine configuration for installed build (used by test-cargo-miri).
 echo "Installing release version of Miri"
-./miri install
-
-echo "Checking various feature flag configurations"
-./miri check --no-default-features # make sure this can be built
-./miri check # and this, too
-# `--all-features` is used for the build below, so no extra check needed.
+time ./miri install
 
 # Prepare debug build for direct `./miri` invocations.
 # We enable all features to make sure the Stacked Borrows consistency check runs.
 echo "Building debug version of Miri"
 export CARGO_EXTRA_FLAGS="$CARGO_EXTRA_FLAGS --all-features"
-./miri build --all-targets # the build that all the `./miri test` below will use
+time ./miri build --all-targets # the build that all the `./miri test` below will use
 
 endgroup
 
-# Test
+# Run tests. Recognizes these variables:
+# - MIRI_TEST_TARGET: the target to test. Empty for host target.
+# - GC_STRESS: if non-empty, run the GC stress test for the main test suite.
+# - MIR_OPT: if non-empty, re-run test `pass` tests with mir-opt-level=4
+# - MANY_SEEDS: if set to N, run the "many-seeds" tests N times
+# - TEST_BENCH: if non-empty, check that the benchmarks all build
+# - CARGO_MIRI_ENV: if non-empty, set some env vars and config to potentially confuse cargo-miri
 function run_tests {
-  if [ -n "${MIRI_TEST_TARGET:-}" ]; then
+  if [ -n "${MIRI_TEST_TARGET-}" ]; then
     begingroup "Testing foreign architecture $MIRI_TEST_TARGET"
   else
     begingroup "Testing host architecture"
   fi
 
   ## ui test suite
-  # On the host, also stress-test the GC.
-  if [ -z "${MIRI_TEST_TARGET:-}" ]; then
-    MIRIFLAGS="${MIRIFLAGS:-} -Zmiri-provenance-gc=1" ./miri test
+  if [ -n "${GC_STRESS-}" ]; then
+    time MIRIFLAGS="${MIRIFLAGS-} -Zmiri-provenance-gc=1" ./miri test
   else
-    ./miri test
+    time ./miri test
   fi
 
-  # Host-only tests
-  if [ -z "${MIRI_TEST_TARGET:-}" ]; then
-    # Running these on all targets is unlikely to catch more problems and would
-    # cost a lot of CI time.
-
+  ## advanced tests
+  if [ -n "${MIR_OPT-}" ]; then
     # Tests with optimizations (`-O` is what cargo passes, but crank MIR 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.
     # We explicitly enable debug-assertions here, they are disabled by -O but we have tests
     # which exist to check that we panic on debug assertion failures.
-    MIRIFLAGS="${MIRIFLAGS:-} -O -Zmir-opt-level=4 -Cdebug-assertions=yes" MIRI_SKIP_UI_CHECKS=1 ./miri test -- tests/{pass,panic}
-
+    time MIRIFLAGS="${MIRIFLAGS-} -O -Zmir-opt-level=4 -Cdebug-assertions=yes" MIRI_SKIP_UI_CHECKS=1 ./miri test -- tests/{pass,panic}
+  fi
+  if [ -n "${MANY_SEEDS-}" ]; then
     # Also run some many-seeds tests. 64 seeds means this takes around a minute per test.
     # (Need to invoke via explicit `bash -c` for Windows.)
-    for FILE in tests/many-seeds/*.rs; do
-      MIRI_SEEDS=64 ./miri many-seeds "$BASH" -c "./miri run '$FILE'"
+    time for FILE in tests/many-seeds/*.rs; do
+      MIRI_SEEDS=$MANY_SEEDS ./miri many-seeds "$BASH" -c "./miri run '$FILE'"
     done
-
+  fi
+  if [ -n "${TEST_BENCH-}" ]; then
     # Check that the benchmarks build and run, but without actually benchmarking.
-    HYPERFINE="'$BASH' -c" ./miri bench
+    time HYPERFINE="'$BASH' -c" ./miri bench
   fi
 
   ## test-cargo-miri
@@ -91,16 +90,18 @@ function run_tests {
     PYTHON=python
   fi
   # Some environment setup that attempts to confuse the heck out of cargo-miri.
-  if [ "$HOST_TARGET" = x86_64-unknown-linux-gnu ]; then
-    # These act up on Windows (`which miri` produces a filename that does not exist?!?),
-    # so let's do this only on Linux. Also makes sure things work without these set.
-    export RUSTC=$(which rustc) # Produces a warning unless we also set MIRI
+  if [ -n "${CARGO_MIRI_ENV-}" ]; then
+    # These act up on Windows (`which miri` produces a filename that does not exist?!?).
+    # RUSTC is the main thing to set (it changes the first argument our wrapper will see).
+    # Unless MIRI is also set, that produces a warning.
+    export RUSTC=$(which rustc)
     export MIRI=$(rustc +miri --print sysroot)/bin/miri
+    # We entirely ignore other wrappers.
+    mkdir -p .cargo
+    echo 'build.rustc-wrapper = "thisdoesnotexist"' > .cargo/config.toml
   fi
-  mkdir -p .cargo
-  echo 'build.rustc-wrapper = "thisdoesnotexist"' > .cargo/config.toml
   # Run the actual test
-  ${PYTHON} test-cargo-miri/run-test.py
+  time ${PYTHON} test-cargo-miri/run-test.py
   # Clean up
   unset RUSTC MIRI
   rm -rf .cargo
@@ -109,7 +110,7 @@ function run_tests {
 }
 
 function run_tests_minimal {
-  if [ -n "${MIRI_TEST_TARGET:-}" ]; then
+  if [ -n "${MIRI_TEST_TARGET-}" ]; then
     begingroup "Testing MINIMAL foreign architecture $MIRI_TEST_TARGET: only testing $@"
   else
     echo "run_tests_minimal requires MIRI_TEST_TARGET to be set"
@@ -126,38 +127,48 @@ function run_tests_minimal {
 
 ## Main Testing Logic ##
 
-# Host target.
-run_tests
-
-# Extra targets.
 # In particular, fully cover all tier 1 targets.
 case $HOST_TARGET in
   x86_64-unknown-linux-gnu)
+    # Host
+    GC_STRESS=1 MIR_OPT=1 MANY_SEEDS=64 TEST_BENCH=1 CARGO_MIRI_ENV=1 run_tests
+    # Extra tier 1
     MIRI_TEST_TARGET=i686-unknown-linux-gnu run_tests
     MIRI_TEST_TARGET=aarch64-unknown-linux-gnu run_tests
-    MIRI_TEST_TARGET=aarch64-apple-darwin run_tests
     MIRI_TEST_TARGET=i686-pc-windows-gnu run_tests
     MIRI_TEST_TARGET=x86_64-pc-windows-gnu run_tests
+    # Extra tier 2
+    MIRI_TEST_TARGET=aarch64-apple-darwin run_tests
     MIRI_TEST_TARGET=arm-unknown-linux-gnueabi run_tests
-    # Some targets are only partially supported.
+    # Partially supported targets (tier 2)
     MIRI_TEST_TARGET=x86_64-unknown-freebsd run_tests_minimal hello integer vec panic/panic concurrency/simple pthread-threadname libc-getentropy libc-getrandom libc-misc libc-fs atomic env align num_cpus
     MIRI_TEST_TARGET=i686-unknown-freebsd run_tests_minimal hello integer vec panic/panic concurrency/simple pthread-threadname libc-getentropy libc-getrandom libc-misc libc-fs atomic env align num_cpus
-
     MIRI_TEST_TARGET=aarch64-linux-android run_tests_minimal hello integer vec panic/panic
     MIRI_TEST_TARGET=wasm32-wasi run_tests_minimal no_std integer strings wasm
     MIRI_TEST_TARGET=wasm32-unknown-unknown run_tests_minimal no_std integer strings wasm
-    MIRI_TEST_TARGET=thumbv7em-none-eabihf run_tests_minimal no_std # no_std embedded architecture
-    MIRI_TEST_TARGET=tests/avr.json MIRI_NO_STD=1 run_tests_minimal no_std # JSON target file
+    MIRI_TEST_TARGET=thumbv7em-none-eabihf run_tests_minimal no_std
+    # Custom target JSON file
+    MIRI_TEST_TARGET=tests/avr.json MIRI_NO_STD=1 run_tests_minimal no_std
     ;;
   x86_64-apple-darwin)
+    # Host
+    GC_STRESS=1 MIR_OPT=1 MANY_SEEDS=64 TEST_BENCH=1 CARGO_MIRI_ENV=1 run_tests
+    # Extra tier 1
+    MIRI_TEST_TARGET=x86_64-pc-windows-msvc CARGO_MIRI_ENV=1 run_tests
+    # Extra tier 2
     MIRI_TEST_TARGET=s390x-unknown-linux-gnu run_tests # big-endian architecture
-    MIRI_TEST_TARGET=x86_64-pc-windows-msvc run_tests
     ;;
   i686-pc-windows-msvc)
+    # Host
+    # Only smoke-test `many-seeds`; 64 runs take 15min here!
+    GC_STRESS=1 MIR_OPT=1 MANY_SEEDS=1 TEST_BENCH=1 run_tests
+    # Extra tier 1
+    # We really want to ensure a Linux target works on a Windows host,
+    # and a 64bit target works on a 32bit host.
     MIRI_TEST_TARGET=x86_64-unknown-linux-gnu run_tests
     ;;
   *)
-    echo "FATAL: unknown OS"
+    echo "FATAL: unknown host target: $HOST_TARGET"
     exit 1
     ;;
 esac
diff --git a/src/tools/miri/test-cargo-miri/run-test.py b/src/tools/miri/test-cargo-miri/run-test.py
index 21479bc4d58e..cac11dff7755 100755
--- a/src/tools/miri/test-cargo-miri/run-test.py
+++ b/src/tools/miri/test-cargo-miri/run-test.py
@@ -31,11 +31,11 @@ def cargo_miri(cmd, quiet = True):
 
 def normalize_stdout(str):
     str = str.replace("src\\", "src/") # normalize paths across platforms
-    str = re.sub("finished in \d+\.\d\ds", "finished in $TIME", str) # the time keeps changing, obviously
+    str = re.sub("finished in \\d+\\.\\d\\ds", "finished in $TIME", str) # the time keeps changing, obviously
     return str
 
 def normalize_stderr(str):
-    str = re.sub("Preparing a sysroot for Miri \(target: [a-z0-9_-]+\)\.\.\. done\n", "", str) # remove leading cargo-miri setup output
+    str = re.sub("Preparing a sysroot for Miri \\(target: [a-z0-9_-]+\\)\\.\\.\\. done\n", "", str) # remove leading cargo-miri setup output
     return str
 
 def check_output(actual, path, name):