also run compile-fail tests with and without optimizations

src/stacked_borrows.rs

@@ -446,6 +446,8 @@ fn tag_dereference(
                 // A mut got transmuted to shr.  High time we freeze this location!
                 // Make this a delayed reborrow.  Redundant reborows to shr are okay,
                 // so we do not have to be worried about doing too much.
+                // FIXME: Reconsider if we really want to mutate things while doing just a deref,
+                // which, in particular, validation does.
                 trace!("tag_dereference: Lazy freezing of {:?}", ptr);
                 return self.tag_reference(ptr, pointee_ty, size, ref_kind);
             }

tests/compile-fail/stacked_borrows/alias_through_mutation.rs

@@ -1,3 +1,6 @@
+// With optimizations, we just store a raw in `x`, and there is no problem.
+// compile-flags: -Zmir-opt-level=0
+
 #![allow(unused_variables)]
 
 // This makes a ref that was passed to us via &mut alias with things it should not alias with

tests/compile-fail/stacked_borrows/buggy_as_mut_slice.rs

@@ -1,3 +1,6 @@
+// FIXME: Without retagging, optimization kills finding this problem
+// compile-flags: -Zmir-opt-level=0
+
 #![allow(unused_variables)]
 
 mod safe {

tests/compile-fail/stacked_borrows/buggy_split_at_mut.rs

@@ -1,3 +1,6 @@
+// FIXME: Without retagging, optimization kills finding this problem
+// compile-flags: -Zmir-opt-level=0
+
 #![allow(unused_variables)]
 
 mod safe {

tests/compile-fail/stacked_borrows/illegal_write2.rs

@@ -1,3 +1,6 @@
+// The reborow gets optimized away, so we can only detect this issue without optimizations
+// compile-flags: -Zmir-opt-level=0
+
 #![allow(unused_variables)]
 
 fn main() {

tests/compiletest.rs

@@ -37,7 +37,7 @@ fn have_fullmir() -> bool {
     std::env::var("MIRI_SYSROOT").is_ok() || rustc_test_suite().is_some()
 }
 
-fn compile_fail(sysroot: &Path, path: &str, target: &str, host: &str, need_fullmir: bool) {
+fn compile_fail(sysroot: &Path, path: &str, target: &str, host: &str, need_fullmir: bool, opt: bool) {
     if need_fullmir && !have_fullmir() {
         eprintln!("{}", format!(
             "## Skipping compile-fail tests in {} against miri for target {} due to missing mir",
@@ -47,24 +47,34 @@ fn compile_fail(sysroot: &Path, path: &str, target: &str, host: &str, need_fullm
         return;
     }
 
+    let opt_str = if opt { " with optimizations" } else { "" };
     eprintln!("{}", format!(
-        "## Running compile-fail tests in {} against miri for target {}",
+        "## Running compile-fail tests in {} against miri for target {}{}",
         path,
-        target
+        target,
+        opt_str
     ).green().bold());
+
+    let mut flags = Vec::new();
+    flags.push(format!("--sysroot {}", sysroot.display()));
+    flags.push("-Dwarnings -Dunused".to_owned()); // overwrite the -Aunused in compiletest-rs
+    flags.push("-Zmir-emit-validate=1".to_owned());
+    if opt {
+        // Optimizing too aggressivley makes UB detection harder, but test at least
+        // the default value.
+        flags.push("-Zmir-opt-level=1".to_owned());
+    } else {
+        flags.push("-Zmir-opt-level=0".to_owned());
+    }
+
     let mut config = compiletest::Config::default().tempdir();
     config.mode = "compile-fail".parse().expect("Invalid mode");
     config.rustc_path = miri_path();
-    let mut flags = Vec::new();
     if rustc_test_suite().is_some() {
         config.run_lib_path = rustc_lib_path();
         config.compile_lib_path = rustc_lib_path();
     }
-    flags.push(format!("--sysroot {}", sysroot.display()));
-    flags.push("-Dwarnings -Dunused".to_owned()); // overwrite the -Aunused in compiletest-rs
     config.src_base = PathBuf::from(path.to_string());
-    flags.push("-Zmir-opt-level=0".to_owned()); // optimization circumvents some stacked borrow checks
-    flags.push("-Zmir-emit-validate=1".to_owned());
     config.target_rustcflags = Some(flags.join(" "));
     config.target = target.to_owned();
     config.host = host.to_owned();
@@ -88,6 +98,21 @@ fn miri_pass(sysroot: &Path, path: &str, target: &str, host: &str, need_fullmir:
         target,
         opt_str
     ).green().bold());
+
+    let mut flags = Vec::new();
+    flags.push(format!("--sysroot {}", sysroot.display()));
+    flags.push("-Dwarnings -Dunused".to_owned()); // overwrite the -Aunused in compiletest-rs
+    flags.push("-Zmir-emit-validate=1".to_owned());
+    if opt {
+        // FIXME: Using level 1 (instead of 3) for now, as the optimizer is pretty broken
+        // and crashes...
+        // Level 0 and 1 are not the same, so this still gives us *some* coverage.
+        // See https://github.com/rust-lang/rust/issues/50411
+        flags.push("-Zmir-opt-level=1".to_owned());
+    } else {
+        flags.push("-Zmir-opt-level=0".to_owned());
+    }
+
     let mut config = compiletest::Config::default().tempdir();
     config.mode = "ui".parse().expect("Invalid mode");
     config.src_base = PathBuf::from(path);
@@ -98,20 +123,6 @@ fn miri_pass(sysroot: &Path, path: &str, target: &str, host: &str, need_fullmir:
         config.run_lib_path = rustc_lib_path();
         config.compile_lib_path = rustc_lib_path();
     }
-    let mut flags = Vec::new();
-    flags.push(format!("--sysroot {}", sysroot.display()));
-    flags.push("-Dwarnings -Dunused".to_owned()); // overwrite the -Aunused in compiletest-rs
-    if opt {
-        // FIXME: Using level 1 (instead of 3) for now, as the optimizer is pretty broken
-        // and crashes...
-        // Level 0 and 1 are not the same, so this still gives us *some* coverage.
-        // See https://github.com/rust-lang/rust/issues/50411
-        flags.push("-Zmir-opt-level=1".to_owned());
-    } else {
-        flags.push("-Zmir-opt-level=0".to_owned());
-        // For now, only validate without optimizations.  Inlining breaks validation.
-        flags.push("-Zmir-emit-validate=1".to_owned());
-    }
     config.target_rustcflags = Some(flags.join(" "));
     compiletest::run_tests(&config);
 }
@@ -173,13 +184,13 @@ fn run_pass_miri(opt: bool) {
     miri_pass(&sysroot, "tests/run-pass-fullmir", &host, &host, true, opt);
 }
 
-fn compile_fail_miri() {
+fn compile_fail_miri(opt: bool) {
     let sysroot = get_sysroot();
     let host = get_host();
 
     // FIXME: run tests for other targets, too
-    compile_fail(&sysroot, "tests/compile-fail", &host, &host, false);
-    compile_fail(&sysroot, "tests/compile-fail-fullmir", &host, &host, true);
+    compile_fail(&sysroot, "tests/compile-fail", &host, &host, false, opt);
+    compile_fail(&sysroot, "tests/compile-fail-fullmir", &host, &host, true, opt);
 }
 
 #[test]
@@ -191,5 +202,6 @@ fn test() {
     run_pass_miri(false);
     run_pass_miri(true);
 
-    compile_fail_miri();
+    compile_fail_miri(false);
+    compile_fail_miri(true);
 }

tests/run-pass-fullmir/integer-ops.rs

@@ -8,9 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// FIXME: remove -Zmir-opt-level once https://github.com/rust-lang/rust/issues/43359 is fixed
-// compile-flags: -Zmir-opt-level=0
-
 use std::i32;
 
 pub fn main() {