Auto merge of rust-lang#134051 - saethlin:partial-ssa-analysis, r=<try>

Do partial SsaLocals analysis in unoptimized builds

I've been musing about the perf implications of all the queries that `is_freeze` results in. Let's perf it. CI will fail because I'm too lazy to figure out what's going on with the mir-opt tests for now. If perf looks bad, it's not worth fixing the tests.

(it's not like this makes GVN lightweight or light on queries overall, because evaluating consts is still quite a lot of queries)

r? ghost

Author: bors

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.
 ///
@@ -85,7 +85,7 @@ 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/gvn.arithmetic.GVN.panic-unwind.diff

@@ -79,7 +79,6 @@
       let mut _74: u64;
 
       bb0: {
-          StorageLive(_2);
           StorageLive(_3);
           StorageLive(_4);
           _4 = copy _1;
@@ -92,8 +91,6 @@
 
       bb1: {
           StorageDead(_3);
-          StorageDead(_2);
-          StorageLive(_5);
           StorageLive(_6);
           StorageLive(_7);
           _7 = copy _1;
@@ -106,8 +103,6 @@
 
       bb2: {
           StorageDead(_6);
-          StorageDead(_5);
-          StorageLive(_8);
 -         StorageLive(_9);
 +         nop;
           StorageLive(_10);
@@ -125,8 +120,6 @@
       bb3: {
 -         StorageDead(_9);
 +         nop;
-          StorageDead(_8);
-          StorageLive(_12);
           StorageLive(_13);
           StorageLive(_14);
           _14 = copy _1;
@@ -139,8 +132,6 @@
 
       bb4: {
           StorageDead(_13);
-          StorageDead(_12);
-          StorageLive(_15);
           StorageLive(_16);
           StorageLive(_17);
           _17 = copy _1;
@@ -153,8 +144,6 @@
 
       bb5: {
           StorageDead(_16);
-          StorageDead(_15);
-          StorageLive(_18);
           StorageLive(_19);
           StorageLive(_20);
           _20 = copy _1;
@@ -173,8 +162,6 @@
 
       bb7: {
           StorageDead(_19);
-          StorageDead(_18);
-          StorageLive(_22);
           StorageLive(_23);
           StorageLive(_24);
           _24 = copy _1;
@@ -194,8 +181,6 @@
 
       bb9: {
           StorageDead(_23);
-          StorageDead(_22);
-          StorageLive(_26);
           StorageLive(_27);
           StorageLive(_28);
           _28 = copy _1;
@@ -215,8 +200,6 @@
 
       bb11: {
           StorageDead(_27);
-          StorageDead(_26);
-          StorageLive(_30);
           StorageLive(_31);
           StorageLive(_32);
           _32 = copy _1;
@@ -235,8 +218,6 @@
 
       bb13: {
           StorageDead(_31);
-          StorageDead(_30);
-          StorageLive(_34);
           StorageLive(_35);
           StorageLive(_36);
           _36 = copy _1;
@@ -255,8 +236,6 @@
 
       bb15: {
           StorageDead(_35);
-          StorageDead(_34);
-          StorageLive(_38);
           StorageLive(_39);
           StorageLive(_40);
           _40 = copy _1;
@@ -276,8 +255,6 @@
 
       bb17: {
           StorageDead(_39);
-          StorageDead(_38);
-          StorageLive(_42);
           StorageLive(_43);
           StorageLive(_44);
           _44 = copy _1;
@@ -297,8 +274,6 @@
 
       bb19: {
           StorageDead(_43);
-          StorageDead(_42);
-          StorageLive(_46);
           StorageLive(_47);
           StorageLive(_48);
           _48 = copy _1;
@@ -317,8 +292,6 @@
 
       bb21: {
           StorageDead(_47);
-          StorageDead(_46);
-          StorageLive(_50);
           StorageLive(_51);
           StorageLive(_52);
           _52 = copy _1;
@@ -331,8 +304,6 @@
 
       bb22: {
           StorageDead(_51);
-          StorageDead(_50);
-          StorageLive(_53);
           StorageLive(_54);
           StorageLive(_55);
           _55 = copy _1;
@@ -345,8 +316,6 @@
 
       bb23: {
           StorageDead(_54);
-          StorageDead(_53);
-          StorageLive(_56);
           StorageLive(_57);
           StorageLive(_58);
           _58 = copy _1;
@@ -359,8 +328,6 @@
 
       bb24: {
           StorageDead(_57);
-          StorageDead(_56);
-          StorageLive(_59);
           StorageLive(_60);
           StorageLive(_61);
           _61 = copy _1;
@@ -373,8 +340,6 @@
 
       bb25: {
           StorageDead(_60);
-          StorageDead(_59);
-          StorageLive(_62);
           StorageLive(_63);
           StorageLive(_64);
           _64 = copy _1;
@@ -387,8 +352,6 @@
 
       bb26: {
           StorageDead(_63);
-          StorageDead(_62);
-          StorageLive(_65);
           StorageLive(_66);
           StorageLive(_67);
           _67 = copy _1;
@@ -404,8 +367,6 @@
 
       bb27: {
           StorageDead(_66);
-          StorageDead(_65);
-          StorageLive(_69);
           StorageLive(_70);
           StorageLive(_71);
           _71 = copy _1;
@@ -418,8 +379,6 @@
 
       bb28: {
           StorageDead(_70);
-          StorageDead(_69);
-          StorageLive(_72);
           StorageLive(_73);
           StorageLive(_74);
           _74 = copy _1;
@@ -432,8 +391,6 @@
 
       bb29: {
           StorageDead(_73);
-          StorageDead(_72);
-          _0 = const ();
           return;
       }
   }

tests/mir-opt/gvn.arithmetic_checked.GVN.panic-unwind.diff

@@ -27,7 +27,6 @@
       let mut _22: (u64, bool);
 
       bb0: {
-          StorageLive(_2);
           StorageLive(_3);
           StorageLive(_4);
           _4 = copy _1;
@@ -47,8 +46,6 @@
 
       bb2: {
           StorageDead(_3);
-          StorageDead(_2);
-          StorageLive(_6);
           StorageLive(_7);
           StorageLive(_8);
           _8 = copy _1;
@@ -68,8 +65,6 @@
 
       bb4: {
           StorageDead(_7);
-          StorageDead(_6);
-          StorageLive(_10);
 -         StorageLive(_11);
 +         nop;
           StorageLive(_12);
@@ -94,8 +89,6 @@
       bb6: {
 -         StorageDead(_11);
 +         nop;
-          StorageDead(_10);
-          StorageLive(_15);
           StorageLive(_16);
           StorageLive(_17);
           _17 = copy _1;
@@ -115,8 +108,6 @@
 
       bb8: {
           StorageDead(_16);
-          StorageDead(_15);
-          StorageLive(_19);
           StorageLive(_20);
           StorageLive(_21);
           _21 = copy _1;
@@ -136,8 +127,6 @@
 
       bb10: {
           StorageDead(_20);
-          StorageDead(_19);
-          _0 = const ();
           return;
       }
   }