Add pass to identify undefined or erroneous behaviour

compiler/rustc_session/src/options.rs

@@ -1694,6 +1694,8 @@ options! {
         "link native libraries in the linker invocation (default: yes)"),
     link_only: bool = (false, parse_bool, [TRACKED],
         "link the `.rlink` file generated by `-Z no-link` (default: no)"),
+    lint_mir: bool = (false, parse_bool, [UNTRACKED],
+        "lint MIR before and after each transformation"),
     llvm_module_flag: Vec<(String, u32, String)> = (Vec::new(), parse_llvm_module_flag, [TRACKED],
         "a list of module flags to pass to LLVM (space separated)"),
     llvm_plugins: Vec<String> = (Vec::new(), parse_list, [TRACKED],