Add -Z orbit for forcing MIR for everything, unless #[rustc_no_mir] is used.

configure

@@ -607,6 +607,7 @@ opt dist-host-only 0 "only install bins for the host architecture"
 opt inject-std-version 1 "inject the current compiler version of libstd into programs"
 opt llvm-version-check 1 "check if the LLVM version is supported, build anyway"
 opt rustbuild 0 "use the rust and cargo based build system"
+opt orbit 0 "get MIR where it belongs - everywhere; most importantly, in orbit"
 
 # Optimization and debugging options. These may be overridden by the release channel, etc.
 opt_nosave optimize 1 "build optimized rust code"
@@ -713,6 +714,8 @@ if [ -n "$CFG_ENABLE_DEBUG_ASSERTIONS" ]; then putvar CFG_ENABLE_DEBUG_ASSERTION
 if [ -n "$CFG_ENABLE_DEBUGINFO" ]; then putvar CFG_ENABLE_DEBUGINFO; fi
 if [ -n "$CFG_ENABLE_DEBUG_JEMALLOC" ]; then putvar CFG_ENABLE_DEBUG_JEMALLOC; fi
 
+if [ -n "$CFG_ENABLE_ORBIT" ]; then putvar CFG_ENABLE_ORBIT; fi
+
 # A magic value that allows the compiler to use unstable features
 # during the bootstrap even when doing so would normally be an error
 # because of feature staging or because the build turns on

mk/main.mk

@@ -134,6 +134,11 @@ ifdef CFG_ENABLE_DEBUGINFO
   CFG_RUSTC_FLAGS += -g
 endif
 
+ifdef CFG_ENABLE_ORBIT
+  $(info cfg: launching MIR (CFG_ENABLE_ORBIT))
+  CFG_RUSTC_FLAGS += -Z orbit
+endif
+
 ifdef SAVE_TEMPS
   CFG_RUSTC_FLAGS += --save-temps
 endif

src/librustc/session/config.rs

@@ -663,6 +663,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "print the result of the translation item collection pass"),
     mir_opt_level: Option<usize> = (None, parse_opt_uint,
           "set the MIR optimization level (0-3)"),
+    orbit: bool = (false, parse_bool,
+          "get MIR where it belongs - everywhere; most importantly, in orbit"),
 }
 
 pub fn default_lib_output() -> CrateType {

src/librustc_trans/trans/base.rs

@@ -1431,7 +1431,9 @@ impl<'blk, 'tcx> FunctionContext<'blk, 'tcx> {
         };
 
         let check_attrs = |attrs: &[ast::Attribute]| {
-            attrs.iter().any(|item| item.check_name("rustc_mir"))
+            let default_to_mir = ccx.sess().opts.debugging_opts.orbit;
+            let invert = if default_to_mir { "rustc_no_mir" } else { "rustc_mir" };
+            default_to_mir ^ attrs.iter().any(|item| item.check_name(invert))
         };
 
         let use_mir = if let Some(id) = local_id {
@@ -1449,13 +1451,13 @@ impl<'blk, 'tcx> FunctionContext<'blk, 'tcx> {
         };
 
         FunctionContext {
+            needs_ret_allocas: nested_returns && mir.is_none(),
             mir: mir,
             llfn: llfndecl,
             llretslotptr: Cell::new(None),
             param_env: ccx.tcx().empty_parameter_environment(),
             alloca_insert_pt: Cell::new(None),
             llreturn: Cell::new(None),
-            needs_ret_allocas: nested_returns,
             landingpad_alloca: Cell::new(None),
             lllocals: RefCell::new(NodeMap()),
             llupvars: RefCell::new(NodeMap()),

src/libsyntax/feature_gate.rs

@@ -350,10 +350,14 @@ pub const KNOWN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeGat
                                            "the `#[rustc_move_fragments]` attribute \
                                             is just used for rustc unit tests \
                                             and will never be stable")),
-    ("rustc_mir", Normal, Gated("rustc_attrs",
-                                "the `#[rustc_mir]` attribute \
-                                 is just used for rustc unit tests \
-                                 and will never be stable")),
+    ("rustc_mir", Whitelisted, Gated("rustc_attrs",
+                                     "the `#[rustc_mir]` attribute \
+                                      is just used for rustc unit tests \
+                                      and will never be stable")),
+    ("rustc_no_mir", Whitelisted, Gated("rustc_attrs",
+                                        "the `#[rustc_no_mir]` attribute \
+                                         is just used to make tests pass \
+                                         and will never be stable")),
 
     ("allow_internal_unstable", Normal, Gated("allow_internal_unstable",
                                               EXPLAIN_ALLOW_INTERNAL_UNSTABLE)),