Do partial SsaLocals analysis in unoptimized builds

Author: saethlin

compiler/rustc_mir_transform/src/copy_prop.rs

@@ -5,7 +5,7 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
 use tracing::{debug, instrument};
 
-use crate::ssa::SsaLocals;
+use crate::ssa::{SsaAnalysis, SsaLocals};
 
 /// Unify locals that copy each other.
 ///
@@ -29,7 +29,11 @@ impl<'tcx> crate::MirPass<'tcx> for CopyProp {
         debug!(def_id = ?body.source.def_id());
 
         let typing_env = body.typing_env(tcx);
-        let ssa = SsaLocals::new(tcx, body, typing_env);
+        let ssa_analysis = match tcx.sess.mir_opt_level() {
+            0 | 1 => SsaAnalysis::Partial,
+            _ => SsaAnalysis::Full,
+        };
+        let ssa = SsaLocals::new(tcx, body, typing_env, ssa_analysis);
 
         let fully_moved = fully_moved_locals(&ssa, body);
         debug!(?fully_moved);

compiler/rustc_mir_transform/src/gvn.rs

@@ -107,21 +107,25 @@ use rustc_span::def_id::DefId;
 use smallvec::SmallVec;
 use tracing::{debug, instrument, trace};
 
-use crate::ssa::{AssignedValue, SsaLocals};
+use crate::ssa::{AssignedValue, SsaAnalysis, SsaLocals};
 
 pub(super) struct GVN;
 
 impl<'tcx> crate::MirPass<'tcx> for GVN {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.mir_opt_level() >= 2
+        sess.mir_opt_level() >= 1
     }
 
     #[instrument(level = "trace", skip(self, tcx, body))]
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         debug!(def_id = ?body.source.def_id());
 
         let typing_env = body.typing_env(tcx);
-        let ssa = SsaLocals::new(tcx, body, typing_env);
+        let ssa_analysis = match tcx.sess.mir_opt_level() {
+            0 | 1 => SsaAnalysis::Partial,
+            _ => SsaAnalysis::Full,
+        };
+        let ssa = SsaLocals::new(tcx, body, typing_env, ssa_analysis);
         // Clone dominators because we need them while mutating the body.
         let dominators = body.basic_blocks.dominators().clone();
 

compiler/rustc_mir_transform/src/ref_prop.rs

@@ -11,7 +11,7 @@ use rustc_mir_dataflow::Analysis;
 use rustc_mir_dataflow::impls::{MaybeStorageDead, always_storage_live_locals};
 use tracing::{debug, instrument};
 
-use crate::ssa::{SsaLocals, StorageLiveLocals};
+use crate::ssa::{SsaAnalysis, SsaLocals, StorageLiveLocals};
 
 /// Propagate references using SSA analysis.
 ///
@@ -89,7 +89,7 @@ impl<'tcx> crate::MirPass<'tcx> for ReferencePropagation {
 
 fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
     let typing_env = body.typing_env(tcx);
-    let ssa = SsaLocals::new(tcx, body, typing_env);
+    let ssa = SsaLocals::new(tcx, body, typing_env, SsaAnalysis::Full);
 
     let mut replacer = compute_replacement(tcx, body, &ssa);
     debug!(?replacer.targets);

compiler/rustc_mir_transform/src/ssa.rs

@@ -38,11 +38,17 @@ pub(super) enum AssignedValue<'a, 'tcx> {
     Terminator,
 }
 
+pub(super) enum SsaAnalysis {
+    Full,
+    Partial,
+}
+
 impl SsaLocals {
     pub(super) fn new<'tcx>(
         tcx: TyCtxt<'tcx>,
         body: &Body<'tcx>,
         typing_env: ty::TypingEnv<'tcx>,
+        analysis: SsaAnalysis,
     ) -> SsaLocals {
         let assignment_order = Vec::with_capacity(body.local_decls.len());
 
@@ -79,9 +85,15 @@ impl SsaLocals {
         // borrows, we need to check the types. For raw pointers and mutable borrows, the locals
         // have already been marked as non-SSA.
         debug!(?visitor.borrowed_locals);
+
         for local in visitor.borrowed_locals.iter() {
-            if !body.local_decls[local].ty.is_freeze(tcx, typing_env) {
-                visitor.assignments[local] = Set1::Many;
+            match analysis {
+                SsaAnalysis::Full => {
+                    if !body.local_decls[local].ty.is_freeze(tcx, typing_env) {
+                        visitor.assignments[local] = Set1::Many;
+                    }
+                }
+                SsaAnalysis::Partial => visitor.assignments[local] = Set1::Many,
             }
         }
 

tests/mir-opt/copy-prop/borrowed_local.borrowed.CopyProp.panic-unwind.diff

@@ -7,14 +7,13 @@
       let mut _3: &T;
 
       bb0: {
--         _2 = copy _1;
+          _2 = copy _1;
           _3 = &_1;
           _0 = opaque::<&T>(copy _3) -> [return: bb1, unwind continue];
       }
 
       bb1: {
--         _0 = opaque::<T>(copy _2) -> [return: bb2, unwind continue];
-+         _0 = opaque::<T>(copy _1) -> [return: bb2, unwind continue];
+          _0 = opaque::<T>(copy _2) -> [return: bb2, unwind continue];
       }
 
       bb2: {