Add register_opt_mir_pass to let plugin register mir passes before th…

…e Trans pass.

src/librustc/mir/transform.rs

@@ -19,6 +19,7 @@ use std::rc::Rc;
 use syntax::ast::NodeId;
 
 use std::borrow::Cow;
+use std::mem;
 
 /// Where a specific Mir comes from.
 #[derive(Debug, Copy, Clone)]
@@ -180,6 +181,11 @@ impl<'a, 'tcx> Passes {
         &self.suites[suite.0]
     }
 
+    /// Pushes the list of plugin passes in the list of passes.
+    pub fn push_passes(&mut self, suite: MirSuite, passes: &mut Vec<Rc<MirPass>>) {
+        self.suites[suite.0].extend(mem::replace(passes, vec![]));
+    }
+
     pub fn hooks(&self) -> &[Rc<PassHook>] {
         &self.pass_hooks
     }

src/librustc/session/mod.rs

@@ -36,6 +36,7 @@ use syntax::{ast, codemap};
 use syntax::feature_gate::AttributeType;
 use syntax_pos::{Span, MultiSpan};
 
+use mir::transform::MirPass;
 use rustc_back::{LinkerFlavor, PanicStrategy};
 use rustc_back::target::Target;
 use rustc_data_structures::flock;
@@ -85,6 +86,7 @@ pub struct Session {
     /// in order to avoid redundantly verbose output (Issue #24690).
     pub one_time_diagnostics: RefCell<FxHashSet<(lint::LintId, Option<Span>, String)>>,
     pub plugin_llvm_passes: RefCell<Vec<String>>,
+    pub opt_mir_passes: RefCell<Vec<Rc<MirPass>>>,
     pub plugin_attributes: RefCell<Vec<(String, AttributeType)>>,
     pub crate_types: RefCell<Vec<config::CrateType>>,
     pub dependency_formats: RefCell<dependency_format::Dependencies>,
@@ -711,6 +713,7 @@ pub fn build_session_(sopts: config::Options,
         lints: RefCell::new(lint::LintTable::new()),
         one_time_diagnostics: RefCell::new(FxHashSet()),
         plugin_llvm_passes: RefCell::new(Vec::new()),
+        opt_mir_passes: RefCell::new(Vec::new()),
         plugin_attributes: RefCell::new(Vec::new()),
         crate_types: RefCell::new(Vec::new()),
         dependency_formats: RefCell::new(FxHashMap()),

src/librustc_driver/driver.rs

@@ -618,7 +618,8 @@ pub fn phase_2_configure_and_expand<F>(sess: &Session,
 
     let whitelisted_legacy_custom_derives = registry.take_whitelisted_custom_derives();
     let Registry { syntax_exts, early_lint_passes, late_lint_passes, lint_groups,
-                   llvm_passes, attributes, .. } = registry;
+                   llvm_passes, attributes, opt_mir_passes,
+                   .. } = registry;
 
     sess.track_errors(|| {
         let mut ls = sess.lint_store.borrow_mut();
@@ -634,6 +635,7 @@ pub fn phase_2_configure_and_expand<F>(sess: &Session,
         }
 
         *sess.plugin_llvm_passes.borrow_mut() = llvm_passes;
+        sess.opt_mir_passes.borrow_mut().extend(opt_mir_passes);
         *sess.plugin_attributes.borrow_mut() = attributes.clone();
     })?;
 
@@ -922,7 +924,7 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
     rustc_const_eval::provide(&mut extern_providers);
 
     // Setup the MIR passes that we want to run.
-    let mut passes = Passes::new();
+    let mut passes =  Passes::new();
     passes.push_hook(mir::transform::dump_mir::DumpMir);
 
     // Remove all `EndRegion` statements that are not involved in borrows.
@@ -958,6 +960,9 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
     passes.push_pass(MIR_OPTIMIZED, mir::transform::copy_prop::CopyPropagation);
     passes.push_pass(MIR_OPTIMIZED, mir::transform::simplify::SimplifyLocals);
     passes.push_pass(MIR_OPTIMIZED, mir::transform::add_call_guards::AddCallGuards);
+
+    // Push plugin passes before the convertion phase.
+    passes.push_passes(MIR_OPTIMIZED, &mut sess.opt_mir_passes.borrow_mut());
     passes.push_pass(MIR_OPTIMIZED, mir::transform::dump_mir::Marker("PreTrans"));
 
     TyCtxt::create_and_enter(sess,

src/librustc_plugin/registry.rs

@@ -12,6 +12,7 @@
 
 use rustc::lint::{EarlyLintPassObject, LateLintPassObject, LintId, Lint};
 use rustc::session::Session;
+use rustc::mir::transform::MirPass;
 
 use syntax::ext::base::{SyntaxExtension, NamedSyntaxExtension, NormalTT, IdentTT};
 use syntax::ext::base::MacroExpanderFn;
@@ -22,6 +23,7 @@ use syntax_pos::Span;
 
 use std::collections::HashMap;
 use std::borrow::ToOwned;
+use std::rc::Rc;
 
 /// Structure used to register plugins.
 ///
@@ -51,6 +53,9 @@ pub struct Registry<'a> {
     #[doc(hidden)]
     pub late_lint_passes: Vec<LateLintPassObject>,
 
+    #[doc(hidden)]
+    pub opt_mir_passes: Vec<Rc<MirPass>>,
+
     #[doc(hidden)]
     pub lint_groups: HashMap<&'static str, Vec<LintId>>,
 
@@ -76,6 +81,7 @@ impl<'a> Registry<'a> {
             lint_groups: HashMap::new(),
             llvm_passes: vec![],
             attributes: vec![],
+            opt_mir_passes: Vec::new(),
             whitelisted_custom_derives: Vec::new(),
         }
     }
@@ -152,6 +158,11 @@ impl<'a> Registry<'a> {
         self.lint_groups.insert(name, to.into_iter().map(|x| LintId::of(x)).collect());
     }
 
+    /// Register a MIR pass to be executed at the end of the MIR passes pipeline.
+    pub fn register_opt_mir_pass(&mut self, pass: Rc<MirPass>) {
+        self.opt_mir_passes.push(pass);
+    }
+
     /// Register an LLVM pass.
     ///
     /// Registration with LLVM itself is handled through static C++ objects with