Delete ConstDebugInfo pass

compiler/rustc_mir_transform/src/const_debuginfo.rs

@@ -1,103 +0,0 @@
-//! Finds locals which are assigned once to a const and unused except for debuginfo and converts
-//! their debuginfo to use the const directly, allowing the local to be removed.
-
-use rustc_middle::{
-    mir::{
-        visit::{PlaceContext, Visitor},
-        Body, ConstOperand, Local, Location, Operand, Rvalue, StatementKind, VarDebugInfoContents,
-    },
-    ty::TyCtxt,
-};
-
-use crate::MirPass;
-use rustc_index::{bit_set::BitSet, IndexVec};
-
-pub struct ConstDebugInfo;
-
-impl<'tcx> MirPass<'tcx> for ConstDebugInfo {
-    fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        // Disabled in favour of `SingleUseConsts`
-        sess.mir_opt_level() > 2
-    }
-
-    fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        trace!("running ConstDebugInfo on {:?}", body.source);
-
-        for (local, constant) in find_optimization_opportunities(body) {
-            for debuginfo in &mut body.var_debug_info {
-                if let VarDebugInfoContents::Place(p) = debuginfo.value {
-                    if p.local == local && p.projection.is_empty() {
-                        trace!(
-                            "changing debug info for {:?} from place {:?} to constant {:?}",
-                            debuginfo.name,
-                            p,
-                            constant
-                        );
-                        debuginfo.value = VarDebugInfoContents::Const(constant);
-                    }
-                }
-            }
-        }
-    }
-}
-
-struct LocalUseVisitor {
-    local_mutating_uses: IndexVec<Local, u8>,
-    local_assignment_locations: IndexVec<Local, Option<Location>>,
-}
-
-fn find_optimization_opportunities<'tcx>(body: &Body<'tcx>) -> Vec<(Local, ConstOperand<'tcx>)> {
-    let mut visitor = LocalUseVisitor {
-        local_mutating_uses: IndexVec::from_elem(0, &body.local_decls),
-        local_assignment_locations: IndexVec::from_elem(None, &body.local_decls),
-    };
-
-    visitor.visit_body(body);
-
-    let mut locals_to_debuginfo = BitSet::new_empty(body.local_decls.len());
-    for debuginfo in &body.var_debug_info {
-        if let VarDebugInfoContents::Place(p) = debuginfo.value
-            && let Some(l) = p.as_local()
-        {
-            locals_to_debuginfo.insert(l);
-        }
-    }
-
-    let mut eligible_locals = Vec::new();
-    for (local, mutating_uses) in visitor.local_mutating_uses.drain_enumerated(..) {
-        if mutating_uses != 1 || !locals_to_debuginfo.contains(local) {
-            continue;
-        }
-
-        if let Some(location) = visitor.local_assignment_locations[local] {
-            let bb = &body[location.block];
-
-            // The value is assigned as the result of a call, not a constant
-            if bb.statements.len() == location.statement_index {
-                continue;
-            }
-
-            if let StatementKind::Assign(box (p, Rvalue::Use(Operand::Constant(box c)))) =
-                &bb.statements[location.statement_index].kind
-            {
-                if let Some(local) = p.as_local() {
-                    eligible_locals.push((local, *c));
-                }
-            }
-        }
-    }
-
-    eligible_locals
-}
-
-impl Visitor<'_> for LocalUseVisitor {
-    fn visit_local(&mut self, local: Local, context: PlaceContext, location: Location) {
-        if context.is_mutating_use() {
-            self.local_mutating_uses[local] = self.local_mutating_uses[local].saturating_add(1);
-
-            if context.is_place_assignment() {
-                self.local_assignment_locations[local] = Some(location);
-            }
-        }
-    }
-}

compiler/rustc_mir_transform/src/lib.rs

@@ -55,7 +55,6 @@ mod remove_place_mention;
 // This pass is public to allow external drivers to perform MIR cleanup
 mod add_subtyping_projections;
 pub mod cleanup_post_borrowck;
-mod const_debuginfo;
 mod copy_prop;
 mod coroutine;
 mod cost_checker;
@@ -595,7 +594,6 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
             &simplify::SimplifyLocals::AfterGVN,
             &dataflow_const_prop::DataflowConstProp,
             &single_use_consts::SingleUseConsts,
-            &const_debuginfo::ConstDebugInfo,
             &o1(simplify_branches::SimplifyConstCondition::AfterConstProp),
             &jump_threading::JumpThreading,
             &early_otherwise_branch::EarlyOtherwiseBranch,

tests/mir-opt/const_debuginfo.main.SingleUseConsts.diff

@@ -1,5 +1,5 @@
-- // MIR for `main` before ConstDebugInfo
+- // MIR for `main` before SingleUseConsts
-+ // MIR for `main` after ConstDebugInfo
++ // MIR for `main` after SingleUseConsts
   
   fn main() -> () {
       let mut _0: ();
@@ -56,39 +56,53 @@
   
       bb0: {
           nop;
-          _1 = const 1_u8;
+-         _1 = const 1_u8;
           nop;
-          _2 = const 2_u8;
+-         _2 = const 2_u8;
           nop;
-          _3 = const 3_u8;
+-         _3 = const 3_u8;
++         nop;
++         nop;
++         nop;
           StorageLive(_4);
           StorageLive(_5);
           StorageLive(_6);
-          _6 = const 1_u8;
+-         _6 = const 1_u8;
++         nop;
           StorageLive(_7);
-          _7 = const 2_u8;
+-         _7 = const 2_u8;
-          _5 = const 3_u8;
+-         _5 = const 3_u8;
++         nop;
++         nop;
           StorageDead(_7);
           StorageDead(_6);
           StorageLive(_8);
-          _8 = const 3_u8;
+-         _8 = const 3_u8;
-          _4 = const 6_u8;
+-         _4 = const 6_u8;
++         nop;
++         nop;
           StorageDead(_8);
           StorageDead(_5);
           StorageLive(_9);
-          _9 = const "hello, world!";
+-         _9 = const "hello, world!";
++         nop;
           StorageLive(_10);
           _10 = (const true, const false, const 123_u32);
           StorageLive(_11);
-          _11 = const Option::<u16>::Some(99_u16);
+-         _11 = const Option::<u16>::Some(99_u16);
++         nop;
           StorageLive(_12);
-          _12 = const Point {{ x: 32_u32, y: 32_u32 }};
+-         _12 = const Point {{ x: 32_u32, y: 32_u32 }};
++         nop;
           StorageLive(_13);
           nop;
-          _14 = const 32_u32;
+-         _14 = const 32_u32;
++         nop;
           StorageLive(_15);
-          _15 = const 32_u32;
+-         _15 = const 32_u32;
-          _13 = const 64_u32;
+-         _13 = const 64_u32;
++         nop;
++         nop;
           StorageDead(_15);
           nop;
           _0 = const ();

tests/mir-opt/const_debuginfo.rs

@@ -1,12 +1,14 @@
-//@ test-mir-pass: ConstDebugInfo
+//@ test-mir-pass: SingleUseConsts
 //@ compile-flags: -C overflow-checks=no -Zmir-enable-passes=+GVN
 
+#![allow(unused)]
+
 struct Point {
     x: u32,
     y: u32,
 }
 
-// EMIT_MIR const_debuginfo.main.ConstDebugInfo.diff
+// EMIT_MIR const_debuginfo.main.SingleUseConsts.diff
 fn main() {
     // CHECK-LABEL: fn main(
     // CHECK: debug x => const 1_u8;

tests/mir-opt/inline/issue_106141.outer.Inline.panic-abort.diff

@@ -8,7 +8,7 @@
 +         let mut _2: bool;
 +         let mut _3: bool;
 +         scope 2 {
-+             debug buffer => const inner::promoted[0];
++             debug buffer => _1;
 +             scope 3 {
 +                 debug index => _0;
 +             }

tests/mir-opt/inline/issue_106141.outer.Inline.panic-unwind.diff

@@ -8,7 +8,7 @@
 +         let mut _2: bool;
 +         let mut _3: bool;
 +         scope 2 {
-+             debug buffer => const inner::promoted[0];
++             debug buffer => _1;
 +             scope 3 {
 +                 debug index => _0;
 +             }