Auto merge of #31656 - jonas-schievink:mirdump, r=nrc

This allows obtaining a textual MIR dump for individual items or all items in the crate.

I haven't added any tests since ~~I'm too lazy~~ this is an unstable debugging option, but I'll add one if required.

MIR for a single function can now be dumped using `rustc -Zunstable-options --unpretty mir=my_function` and no longer requires the use of in-source `#[rustc_mir]` attributes.

Blocks rust-lang/rust-playpen#154 (if MIR dump support from the playpen is even wanted).

Example output:
```rust
fn main() {
    let x = Some(0);
    x.unwrap_or_else(|| 1);
}
```

```
MIR for expr || 1 (id=16)
fn(arg0: [closure@test.rs:3:22: 3:26]) -> i32 {
    let mut tmp0: ();

    bb0: {
        return = const 1;
        goto -> bb1;
    }

    bb1: {
        return;
    }
}
MIR for fn main::main (id=4)
fn() -> () {
    let var0: core::option::Option<i32>; // x
    let mut tmp0: ();
    let mut tmp1: i32;
    let mut tmp2: core::option::Option<i32>;
    let mut tmp3: [closure@test.rs:3:22: 3:26];

    bb0: {
        var0 = core::option::Option::Some(const 0);
        tmp2 = var0;
        tmp3 = [closure@test.rs:3:22: 3:26];
        tmp1 = core::option::Option<T>::unwrap_or_else(tmp2, tmp3) -> bb2;
    }

    bb1: {
        return;
    }

    bb2: {
        drop(tmp1) -> bb3;
    }

    bb3: {
        return = ();
        goto -> bb1;
    }
}
```

1 files changed, 49 insertions, 1 deletions

diff --git a/src/librustc_driver/pretty.rs b/src/librustc_driver/pretty.rs
index 4a82aa72825..05173578921 100644
--- a/src/librustc_driver/pretty.rs
+++ b/src/librustc_driver/pretty.rs
@@ -30,6 +30,8 @@ use rustc_borrowck::graphviz as borrowck_dot;
 use rustc_resolve as resolve;
 use rustc_metadata::cstore::CStore;
 
+use rustc_mir::pretty::write_mir_pretty;
+
 use syntax::ast::{self, BlockCheckMode};
 use syntax::codemap;
 use syntax::fold::{self, Folder};
@@ -77,6 +79,7 @@ pub enum PpMode {
     PpmSource(PpSourceMode),
     PpmHir(PpSourceMode),
     PpmFlowGraph(PpFlowGraphMode),
+    PpmMir,
 }
 
 pub fn parse_pretty(sess: &Session,
@@ -96,6 +99,7 @@ pub fn parse_pretty(sess: &Session,
         ("hir", true) => PpmHir(PpmNormal),
         ("hir,identified", true) => PpmHir(PpmIdentified),
         ("hir,typed", true) => PpmHir(PpmTyped),
+        ("mir", true) => PpmMir,
         ("flowgraph", true) => PpmFlowGraph(PpFlowGraphMode::Default),
         ("flowgraph,unlabelled", true) => PpmFlowGraph(PpFlowGraphMode::UnlabelledEdges),
         _ => {
@@ -103,7 +107,7 @@ pub fn parse_pretty(sess: &Session,
                 sess.fatal(&format!("argument to `unpretty` must be one of `normal`, \
                                      `expanded`, `flowgraph[,unlabelled]=<nodeid>`, \
                                      `identified`, `expanded,identified`, `everybody_loops`, \
-                                     `hir`, `hir,identified`, or `hir,typed`; got {}",
+                                     `hir`, `hir,identified`, `hir,typed`, or `mir`; got {}",
                                     name));
             } else {
                 sess.fatal(&format!("argument to `pretty` must be one of `normal`, `expanded`, \
@@ -569,6 +573,7 @@ fn needs_ast_map(ppm: &PpMode, opt_uii: &Option<UserIdentifiedItem>) -> bool {
         PpmSource(PpmExpandedIdentified) |
         PpmSource(PpmExpandedHygiene) |
         PpmHir(_) |
+        PpmMir |
         PpmFlowGraph(_) => true,
         PpmSource(PpmTyped) => panic!("invalid state"),
     }
@@ -584,6 +589,7 @@ fn needs_expansion(ppm: &PpMode) -> bool {
         PpmSource(PpmExpandedIdentified) |
         PpmSource(PpmExpandedHygiene) |
         PpmHir(_) |
+        PpmMir |
         PpmFlowGraph(_) => true,
         PpmSource(PpmTyped) => panic!("invalid state"),
     }
@@ -801,6 +807,48 @@ pub fn pretty_print_input(sess: Session,
             })
         }
 
+        (PpmMir, None) => {
+            debug!("pretty printing MIR for whole crate");
+            let ast_map = ast_map.expect("--unpretty mir missing ast_map");
+            abort_on_err(driver::phase_3_run_analysis_passes(&sess,
+                                                             &cstore,
+                                                             ast_map,
+                                                             &arenas,
+                                                             &id,
+                                                             resolve::MakeGlobMap::No,
+                                                             |tcx, mir_map, _, _| {
+                let mir_map = mir_map.unwrap();
+
+                for (nodeid, mir) in &mir_map.map {
+                    try!(writeln!(out, "MIR for {}", tcx.map.node_to_string(*nodeid)));
+                    try!(write_mir_pretty(mir, &mut out));
+                }
+
+                Ok(())
+            }), &sess)
+        }
+
+        (PpmMir, Some(uii)) => {
+            debug!("pretty printing MIR for {:?}", uii);
+            let ast_map = ast_map.expect("--unpretty mir missing ast_map");
+            let nodeid = uii.to_one_node_id("--unpretty", &sess, &ast_map);
+
+            abort_on_err(driver::phase_3_run_analysis_passes(&sess,
+                                                             &cstore,
+                                                             ast_map,
+                                                             &arenas,
+                                                             &id,
+                                                             resolve::MakeGlobMap::No,
+                                                             |tcx, mir_map, _, _| {
+                let mir_map = mir_map.unwrap();
+                try!(writeln!(out, "MIR for {}", tcx.map.node_to_string(nodeid)));
+                let mir = mir_map.map.get(&nodeid).unwrap_or_else(|| {
+                    sess.fatal(&format!("no MIR map entry for node {}", nodeid))
+                });
+                write_mir_pretty(mir, &mut out)
+            }), &sess)
+        }
+
         (PpmFlowGraph(mode), opt_uii) => {
             debug!("pretty printing flow graph for {:?}", opt_uii);
             let uii = opt_uii.unwrap_or_else(|| {