do more cross-testing

.travis.yml

@@ -21,8 +21,6 @@ env:
   - RUST_BACKTRACE=1
 
 before_script:
-# Linux: install extra stuff for cross-compilation
-- if [[ "$TRAVIS_OS_NAME" == linux ]]; then sudo apt update && sudo apt install gcc-multilib; fi
 # Compute the rust version we use. We do not use "language: rust" to have more control here.
 - |
   if [[ "$TRAVIS_EVENT_TYPE" == cron ]]; then

travis.sh

@@ -2,9 +2,6 @@
 set -euo pipefail
 
 # Determine configuration
-if [ "$TRAVIS_OS_NAME" == linux ]; then
-  FOREIGN_TARGET=i686-unknown-linux-gnu
-fi
 export CARGO_EXTRA_FLAGS="--all-features"
 export RUSTC_EXTRA_FLAGS="-D warnings"
 
@@ -16,19 +13,29 @@ echo
 
 # Test
 function run_tests {
-    ./miri test --locked
+  if [ -n "${FOREIGN_TARGET+exists}" ]; then
+    echo "Testing foreign architecture $FOREIGN_TARGET"
+  else
+    echo "Testing host architecture"
+  fi
+
+  ./miri test --locked
+  if ! [ -n "${FOREIGN_TARGET+exists}" ]; then
+    # Only for host architecture: tests with MIR optimizations
     MIRI_TEST_FLAGS="-Z mir-opt-level=3" ./miri test
-    # "miri test" has built the sysroot for us, now this should pass without
-    # any interactive questions.
-    test-cargo-miri/run-test.py
+  fi
+  # "miri test" has built the sysroot for us, now this should pass without
+  # any interactive questions.
+  test-cargo-miri/run-test.py
+
+  echo
 }
 
-echo "Test host architecture"
+# host
 run_tests
-echo
-
-if [ -n "${FOREIGN_TARGET+exists}" ]; then
-  echo "Test foreign architecture ($FOREIGN_TARGET)"
-  MIRI_TEST_TARGET="$FOREIGN_TARGET" run_tests
-  echo
+# cross-test 32bit Linux from everywhere
+MIRI_TEST_TARGET=i686-unknown-linux-gnu run_tests
+if [ "$TRAVIS_OS_NAME" == linux ]; then
+  # cross-test 64bit macOS from Linux
+  FOREIGN_TARGET=x86_64-apple-darwin run_tests
 fi