Auto merge of rust-lang#91475 - ecstatic-morse:mir-pass-manager3, r=oli-obk

Add a MIR pass manager (Taylor's Version)

The final draft of rust-lang#91386 and rust-lang#77665.

While the compile-time constraints in rust-lang#91386 are cool, I decided on a more minimal approach for now. I want to explore phase constraints and maybe relative-ordering constraints in the future, though. This should preserve existing behavior **exactly** (please let me know if it doesn't) while making the following changes to the way we organize things today:

- Each `MirPhase` now corresponds to a single MIR pass. `run_passes` is not responsible for listing the correct MIR phase.
- `run_passes` no longer silently skips passes if the declared MIR phase is greater than or equal to the body's. This has bitten me multiple times. If you want this behavior, you can always branch on `body.phase` yourself.
- If your pass is solely to emit errors, you can use the `MirLint` interface instead, which gets a shared reference to `Body` instead of a mutable one. By differentiating the two, I hope to make it clearer in the short term where lints belong in the pipeline. In the long term perhaps we could enforce this at compile-time?
- MIR is no longer dumped for passes that aren't enabled, or for lints.

I tried to check that `-Zvalidate` still works correctly, since the MIR phase is now updated as soon as the associated pass is done, instead of at the end of all the passes in `run_passes`. However, it looks like `-Zvalidate` is broken with current nightlies anyways 😢 (it spits out a bunch of errors).

cc `@oli-obk` `@wesleywiser`

r? rust-lang/wg-mir-opt

Author: bors

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -41,6 +41,10 @@ pub struct PromoteTemps<'tcx> {
 }
 
 impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> {
+    fn phase_change(&self) -> Option<MirPhase> {
+        Some(MirPhase::ConstPromotion)
+    }
+
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         // There's not really any point in promoting errorful MIR.
         //

compiler/rustc_middle/src/mir/mod.rs

@@ -16,6 +16,7 @@ use rustc_hir::def::{CtorKind, Namespace};
 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
 use rustc_hir::{self, GeneratorKind};
 use rustc_hir::{self as hir, HirId};
+use rustc_session::Session;
 use rustc_target::abi::{Size, VariantIdx};
 
 use polonius_engine::Atom;
@@ -99,7 +100,21 @@ pub trait MirPass<'tcx> {
         }
     }
 
+    /// Returns `true` if this pass is enabled with the current combination of compiler flags.
+    fn is_enabled(&self, _sess: &Session) -> bool {
+        true
+    }
+
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>);
+
+    /// If this pass causes the MIR to enter a new phase, return that phase.
+    fn phase_change(&self) -> Option<MirPhase> {
+        None
+    }
+
+    fn is_mir_dump_enabled(&self) -> bool {
+        true
+    }
 }
 
 /// The various "big phases" that MIR goes through.

compiler/rustc_mir_dataflow/src/rustc_peek.rs

@@ -20,6 +20,7 @@ use crate::{Analysis, JoinSemiLattice, Results, ResultsCursor};
 
 pub struct SanityCheck;
 
+// FIXME: This should be a `MirLint`, but it needs to be moved back to `rustc_mir_transform` first.
 impl<'tcx> MirPass<'tcx> for SanityCheck {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         use crate::has_rustc_mir_with;

compiler/rustc_mir_transform/src/add_retag.rs

@@ -58,11 +58,11 @@ fn may_be_reference(ty: Ty<'tcx>) -> bool {
 }
 
 impl<'tcx> MirPass<'tcx> for AddRetag {
-    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if !tcx.sess.opts.debugging_opts.mir_emit_retag {
-            return;
-        }
+    fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
+        sess.opts.debugging_opts.mir_emit_retag
+    }
 
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         // We need an `AllCallEdges` pass before we can do any work.
         super::add_call_guards::AllCallEdges.run_pass(tcx, body);
 

compiler/rustc_mir_transform/src/check_const_item_mutation.rs

@@ -6,12 +6,12 @@ use rustc_middle::ty::TyCtxt;
 use rustc_session::lint::builtin::CONST_ITEM_MUTATION;
 use rustc_span::def_id::DefId;
 
-use crate::MirPass;
+use crate::MirLint;
 
 pub struct CheckConstItemMutation;
 
-impl<'tcx> MirPass<'tcx> for CheckConstItemMutation {
-    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+impl<'tcx> MirLint<'tcx> for CheckConstItemMutation {
+    fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
         let mut checker = ConstMutationChecker { body, tcx, target_local: None };
         checker.visit_body(&body);
     }

compiler/rustc_mir_transform/src/check_packed_ref.rs

@@ -7,16 +7,16 @@ use rustc_session::lint::builtin::UNALIGNED_REFERENCES;
 use rustc_span::symbol::sym;
 
 use crate::util;
-use crate::MirPass;
+use crate::MirLint;
 
 pub(crate) fn provide(providers: &mut Providers) {
     *providers = Providers { unsafe_derive_on_repr_packed, ..*providers };
 }
 
 pub struct CheckPackedRef;
 
-impl<'tcx> MirPass<'tcx> for CheckPackedRef {
-    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+impl<'tcx> MirLint<'tcx> for CheckPackedRef {
+    fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
         let param_env = tcx.param_env(body.source.def_id());
         let source_info = SourceInfo::outermost(body.span);
         let mut checker = PackedRefChecker { body, tcx, param_env, source_info };

compiler/rustc_mir_transform/src/const_debuginfo.rs

@@ -15,11 +15,11 @@ use rustc_index::{bit_set::BitSet, vec::IndexVec};
 pub struct ConstDebugInfo;
 
 impl<'tcx> MirPass<'tcx> for ConstDebugInfo {
-    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if !tcx.sess.opts.debugging_opts.unsound_mir_opts {
-            return;
-        }
+    fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
+        sess.opts.debugging_opts.unsound_mir_opts && sess.mir_opt_level() > 0
+    }
 
+    fn run_pass(&self, _: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         trace!("running ConstDebugInfo on {:?}", body.source);
 
         for (local, constant) in find_optimization_oportunities(body) {

compiler/rustc_mir_transform/src/const_goto.rs

@@ -27,10 +27,11 @@ use super::simplify::{simplify_cfg, simplify_locals};
 pub struct ConstGoto;
 
 impl<'tcx> MirPass<'tcx> for ConstGoto {
+    fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
+        sess.mir_opt_level() >= 4
+    }
+
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if tcx.sess.mir_opt_level() < 4 {
-            return;
-        }
         trace!("Running ConstGoto on {:?}", body.source);
         let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
         let mut opt_finder =

compiler/rustc_mir_transform/src/const_prop.rs

@@ -62,6 +62,13 @@ macro_rules! throw_machine_stop_str {
 pub struct ConstProp;
 
 impl<'tcx> MirPass<'tcx> for ConstProp {
+    fn is_enabled(&self, _sess: &rustc_session::Session) -> bool {
+        // FIXME(#70073): Unlike the other passes in "optimizations", this one emits errors, so it
+        // runs even when MIR optimizations are disabled. We should separate the lint out from the
+        // transform and move the lint as early in the pipeline as possible.
+        true
+    }
+
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         // will be evaluated by miri and produce its errors there
         if body.source.promoted.is_some() {

compiler/rustc_mir_transform/src/coverage/mod.rs

@@ -49,6 +49,10 @@ impl Error {
 pub struct InstrumentCoverage;
 
 impl<'tcx> MirPass<'tcx> for InstrumentCoverage {
+    fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
+        sess.instrument_coverage()
+    }
+
     fn run_pass(&self, tcx: TyCtxt<'tcx>, mir_body: &mut mir::Body<'tcx>) {
         let mir_source = mir_body.source;