Fix debugger stepping for consts assigned to local vars

compiler/rustc_mir_transform/src/lib.rs

@@ -194,7 +194,7 @@ declare_passes! {
         Final
     };
     mod simplify_comparison_integral : SimplifyComparisonIntegral;
-    mod single_use_consts : SingleUseConsts;
+    mod single_use_consts : SingleUseConsts { TempOnly, Full };
     mod sroa : ScalarReplacementOfAggregates;
     mod strip_debuginfo : StripDebugInfo;
     mod unreachable_enum_branching : UnreachableEnumBranching;
@@ -710,7 +710,8 @@ pub(crate) fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'
             &simplify::SimplifyLocals::AfterGVN,
             &match_branches::MatchBranchSimplification,
             &dataflow_const_prop::DataflowConstProp,
-            &single_use_consts::SingleUseConsts,
+            &single_use_consts::SingleUseConsts::TempOnly,
+            &single_use_consts::SingleUseConsts::Full,
             &o1(simplify_branches::SimplifyConstCondition::AfterConstProp),
             &jump_threading::JumpThreading,
             &early_otherwise_branch::EarlyOtherwiseBranch,

compiler/rustc_mir_transform/src/single_use_consts.rs

@@ -19,11 +19,24 @@ use rustc_middle::ty::TyCtxt;
 ///
 /// It also removes *never*-used constants, since it had all the information
 /// needed to do that too, including updating the debug info.
-pub(super) struct SingleUseConsts;
+pub(super) enum SingleUseConsts {
+    TempOnly,
+    Full,
+}
 
 impl<'tcx> crate::MirPass<'tcx> for SingleUseConsts {
+    fn name(&self) -> &'static str {
+        match self {
+            SingleUseConsts::TempOnly => "SingleUseConsts-temp-only",
+            SingleUseConsts::Full => "SingleUseConsts-full",
+        }
+    }
+
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.mir_opt_level() > 0
+        match self {
+            SingleUseConsts::TempOnly => sess.mir_opt_level() == 1,
+            SingleUseConsts::Full => sess.mir_opt_level() > 1,
+        }
     }
 
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
@@ -46,6 +59,11 @@ impl<'tcx> crate::MirPass<'tcx> for SingleUseConsts {
                 continue;
             };
 
+            let local_has_debug_info = finder.locals_in_debug_info.contains(local);
+            if local_has_debug_info && matches!(self, SingleUseConsts::TempOnly) {
+                continue;
+            }
+
             // We're only changing an operand, not the terminator kinds or successors
             let basic_blocks = body.basic_blocks.as_mut_preserves_cfg();
             let init_statement_kind = std::mem::replace(
@@ -61,7 +79,7 @@ impl<'tcx> crate::MirPass<'tcx> for SingleUseConsts {
 
             let mut replacer = LocalReplacer { tcx, local, operand: Some(operand) };
 
-            if finder.locals_in_debug_info.contains(local) {
+            if local_has_debug_info {
                 for var_debug_info in &mut body.var_debug_info {
                     replacer.visit_var_debug_info(var_debug_info);
                 }

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

@@ -1,5 +1,5 @@
-- // MIR for `main` before SingleUseConsts
-+ // MIR for `main` after SingleUseConsts
+- // MIR for `main` before SingleUseConsts-full
++ // MIR for `main` after SingleUseConsts-full
 
   fn main() -> () {
       let mut _0: ();

tests/mir-opt/const_debuginfo.rs

@@ -1,4 +1,4 @@
-//@ test-mir-pass: SingleUseConsts
+//@ test-mir-pass: SingleUseConsts-full
 //@ compile-flags: -C overflow-checks=no -Zmir-enable-passes=+GVN -Zdump-mir-exclude-alloc-bytes
 
 #![allow(unused)]
@@ -8,7 +8,7 @@ struct Point {
     y: u32,
 }
 
-// EMIT_MIR const_debuginfo.main.SingleUseConsts.diff
+// EMIT_MIR const_debuginfo.main.SingleUseConsts-full.diff
 fn main() {
     // CHECK-LABEL: fn main(
     // CHECK: debug x => const 1_u8;

tests/mir-opt/single_use_consts.assign_const_to_return.SingleUseConsts.panic-abort.diff → tests/mir-opt/single_use_consts.assign_const_to_return.SingleUseConsts-temp-only.panic-abort.diff

@@ -1,5 +1,5 @@
-- // MIR for `assign_const_to_return` before SingleUseConsts
-+ // MIR for `assign_const_to_return` after SingleUseConsts
+- // MIR for `assign_const_to_return` before SingleUseConsts-temp-only
++ // MIR for `assign_const_to_return` after SingleUseConsts-temp-only
 
   fn assign_const_to_return() -> bool {
       let mut _0: bool;

tests/mir-opt/single_use_consts.assign_const_to_return.SingleUseConsts.panic-unwind.diff → tests/mir-opt/single_use_consts.assign_const_to_return.SingleUseConsts-temp-only.panic-unwind.diff

@@ -1,5 +1,5 @@
-- // MIR for `assign_const_to_return` before SingleUseConsts
-+ // MIR for `assign_const_to_return` after SingleUseConsts
+- // MIR for `assign_const_to_return` before SingleUseConsts-temp-only
++ // MIR for `assign_const_to_return` after SingleUseConsts-temp-only
 
   fn assign_const_to_return() -> bool {
       let mut _0: bool;

tests/mir-opt/single_use_consts.if_const.SingleUseConsts.panic-unwind.diff → tests/mir-opt/single_use_consts.if_const.SingleUseConsts-temp-only.panic-abort.diff

@@ -1,5 +1,5 @@
-- // MIR for `if_const` before SingleUseConsts
-+ // MIR for `if_const` after SingleUseConsts
+- // MIR for `if_const` before SingleUseConsts-temp-only
++ // MIR for `if_const` after SingleUseConsts-temp-only
 
   fn if_const() -> i32 {
       let mut _0: i32;

tests/mir-opt/single_use_consts.if_const.SingleUseConsts.panic-abort.diff → tests/mir-opt/single_use_consts.if_const.SingleUseConsts-temp-only.panic-unwind.diff

@@ -1,5 +1,5 @@
-- // MIR for `if_const` before SingleUseConsts
-+ // MIR for `if_const` after SingleUseConsts
+- // MIR for `if_const` before SingleUseConsts-temp-only
++ // MIR for `if_const` after SingleUseConsts-temp-only
 
   fn if_const() -> i32 {
       let mut _0: i32;

tests/mir-opt/single_use_consts.if_const_debug.SingleUseConsts.panic-abort.diff → tests/mir-opt/single_use_consts.if_const_debug.SingleUseConsts-temp-only.panic-abort.diff

@@ -1,29 +1,26 @@
-- // MIR for `if_const_debug` before SingleUseConsts
-+ // MIR for `if_const_debug` after SingleUseConsts
+- // MIR for `if_const_debug` before SingleUseConsts-temp-only
++ // MIR for `if_const_debug` after SingleUseConsts-temp-only
 
   fn if_const_debug() -> i32 {
       let mut _0: i32;
       let _1: bool;
       let _2: ();
       let mut _3: bool;
       scope 1 {
--         debug my_bool => _1;
-+         debug my_bool => const <T as MyTrait>::ASSOC_BOOL;
+          debug my_bool => _1;
       }
 
       bb0: {
           StorageLive(_1);
--         _1 = const <T as MyTrait>::ASSOC_BOOL;
-+         nop;
+          _1 = const <T as MyTrait>::ASSOC_BOOL;
           StorageLive(_2);
           _2 = do_whatever() -> [return: bb1, unwind unreachable];
       }
 
       bb1: {
           StorageDead(_2);
           StorageLive(_3);
--         _3 = copy _1;
-+         _3 = const <T as MyTrait>::ASSOC_BOOL;
+          _3 = copy _1;
           switchInt(move _3) -> [0: bb3, otherwise: bb2];
       }
 

tests/mir-opt/single_use_consts.if_const_debug.SingleUseConsts.panic-unwind.diff → tests/mir-opt/single_use_consts.if_const_debug.SingleUseConsts-temp-only.panic-unwind.diff

@@ -1,29 +1,26 @@
-- // MIR for `if_const_debug` before SingleUseConsts
-+ // MIR for `if_const_debug` after SingleUseConsts
+- // MIR for `if_const_debug` before SingleUseConsts-temp-only
++ // MIR for `if_const_debug` after SingleUseConsts-temp-only
 
   fn if_const_debug() -> i32 {
       let mut _0: i32;
       let _1: bool;
       let _2: ();
       let mut _3: bool;
       scope 1 {
--         debug my_bool => _1;
-+         debug my_bool => const <T as MyTrait>::ASSOC_BOOL;
+          debug my_bool => _1;
       }
 
       bb0: {
           StorageLive(_1);
--         _1 = const <T as MyTrait>::ASSOC_BOOL;
-+         nop;
+          _1 = const <T as MyTrait>::ASSOC_BOOL;
           StorageLive(_2);
           _2 = do_whatever() -> [return: bb1, unwind continue];
       }
 
       bb1: {
           StorageDead(_2);
           StorageLive(_3);
--         _3 = copy _1;
-+         _3 = const <T as MyTrait>::ASSOC_BOOL;
+          _3 = copy _1;
           switchInt(move _3) -> [0: bb3, otherwise: bb2];
       }
 

tests/mir-opt/single_use_consts.keep_parameter.SingleUseConsts.panic-abort.diff → tests/mir-opt/single_use_consts.keep_parameter.SingleUseConsts-temp-only.panic-abort.diff

@@ -1,5 +1,5 @@
-- // MIR for `keep_parameter` before SingleUseConsts
-+ // MIR for `keep_parameter` after SingleUseConsts
+- // MIR for `keep_parameter` before SingleUseConsts-temp-only
++ // MIR for `keep_parameter` after SingleUseConsts-temp-only
 
   fn keep_parameter(_1: i32) -> () {
       debug other => _1;

tests/mir-opt/single_use_consts.keep_parameter.SingleUseConsts.panic-unwind.diff → tests/mir-opt/single_use_consts.keep_parameter.SingleUseConsts-temp-only.panic-unwind.diff

@@ -1,5 +1,5 @@
-- // MIR for `keep_parameter` before SingleUseConsts
-+ // MIR for `keep_parameter` after SingleUseConsts
+- // MIR for `keep_parameter` before SingleUseConsts-temp-only
++ // MIR for `keep_parameter` after SingleUseConsts-temp-only
 
   fn keep_parameter(_1: i32) -> () {
       debug other => _1;

tests/mir-opt/single_use_consts.match_const.SingleUseConsts.panic-abort.diff → tests/mir-opt/single_use_consts.match_const.SingleUseConsts-temp-only.panic-abort.diff

@@ -1,5 +1,5 @@
-- // MIR for `match_const` before SingleUseConsts
-+ // MIR for `match_const` after SingleUseConsts
+- // MIR for `match_const` before SingleUseConsts-temp-only
++ // MIR for `match_const` after SingleUseConsts-temp-only
 
   fn match_const() -> &str {
       let mut _0: &str;

tests/mir-opt/single_use_consts.match_const.SingleUseConsts.panic-unwind.diff → tests/mir-opt/single_use_consts.match_const.SingleUseConsts-temp-only.panic-unwind.diff

@@ -1,5 +1,5 @@
-- // MIR for `match_const` before SingleUseConsts
-+ // MIR for `match_const` after SingleUseConsts
+- // MIR for `match_const` before SingleUseConsts-temp-only
++ // MIR for `match_const` after SingleUseConsts-temp-only
 
   fn match_const() -> &str {
       let mut _0: &str;

tests/mir-opt/single_use_consts.match_const_debug.SingleUseConsts.panic-abort.diff → tests/mir-opt/single_use_consts.match_const_debug.SingleUseConsts-temp-only.panic-abort.diff

@@ -1,27 +1,24 @@
-- // MIR for `match_const_debug` before SingleUseConsts
-+ // MIR for `match_const_debug` after SingleUseConsts
+- // MIR for `match_const_debug` before SingleUseConsts-temp-only
++ // MIR for `match_const_debug` after SingleUseConsts-temp-only
 
   fn match_const_debug() -> &str {
       let mut _0: &str;
       let _1: i32;
       let _2: ();
       scope 1 {
--         debug my_int => _1;
-+         debug my_int => const <T as MyTrait>::ASSOC_INT;
+          debug my_int => _1;
       }
 
       bb0: {
           StorageLive(_1);
--         _1 = const <T as MyTrait>::ASSOC_INT;
-+         nop;
+          _1 = const <T as MyTrait>::ASSOC_INT;
           StorageLive(_2);
           _2 = do_whatever() -> [return: bb1, unwind unreachable];
       }
 
       bb1: {
           StorageDead(_2);
--         switchInt(copy _1) -> [7: bb4, 42: bb3, otherwise: bb2];
-+         switchInt(const <T as MyTrait>::ASSOC_INT) -> [7: bb4, 42: bb3, otherwise: bb2];
+          switchInt(copy _1) -> [7: bb4, 42: bb3, otherwise: bb2];
       }
 
       bb2: {

tests/mir-opt/single_use_consts.match_const_debug.SingleUseConsts.panic-unwind.diff → tests/mir-opt/single_use_consts.match_const_debug.SingleUseConsts-temp-only.panic-unwind.diff

@@ -1,27 +1,24 @@
-- // MIR for `match_const_debug` before SingleUseConsts
-+ // MIR for `match_const_debug` after SingleUseConsts
+- // MIR for `match_const_debug` before SingleUseConsts-temp-only
++ // MIR for `match_const_debug` after SingleUseConsts-temp-only
 
   fn match_const_debug() -> &str {
       let mut _0: &str;
       let _1: i32;
       let _2: ();
       scope 1 {
--         debug my_int => _1;
-+         debug my_int => const <T as MyTrait>::ASSOC_INT;
+          debug my_int => _1;
       }
 
       bb0: {
           StorageLive(_1);
--         _1 = const <T as MyTrait>::ASSOC_INT;
-+         nop;
+          _1 = const <T as MyTrait>::ASSOC_INT;
           StorageLive(_2);
           _2 = do_whatever() -> [return: bb1, unwind continue];
       }
 
       bb1: {
           StorageDead(_2);
--         switchInt(copy _1) -> [7: bb4, 42: bb3, otherwise: bb2];
-+         switchInt(const <T as MyTrait>::ASSOC_INT) -> [7: bb4, 42: bb3, otherwise: bb2];
+          switchInt(copy _1) -> [7: bb4, 42: bb3, otherwise: bb2];
       }
 
       bb2: {

tests/mir-opt/single_use_consts.never_used_debug.SingleUseConsts-temp-only.panic-abort.diff

@@ -0,0 +1,19 @@
+- // MIR for `never_used_debug` before SingleUseConsts-temp-only
++ // MIR for `never_used_debug` after SingleUseConsts-temp-only
+
+  fn never_used_debug() -> () {
+      let mut _0: ();
+      let _1: i32;
+      scope 1 {
+          debug my_int => _1;
+      }
+
+      bb0: {
+          StorageLive(_1);
+          _1 = const <T as MyTrait>::ASSOC_INT;
+          _0 = const ();
+          StorageDead(_1);
+          return;
+      }
+  }
+

tests/mir-opt/single_use_consts.never_used_debug.SingleUseConsts-temp-only.panic-unwind.diff

@@ -0,0 +1,19 @@
+- // MIR for `never_used_debug` before SingleUseConsts-temp-only
++ // MIR for `never_used_debug` after SingleUseConsts-temp-only
+
+  fn never_used_debug() -> () {
+      let mut _0: ();
+      let _1: i32;
+      scope 1 {
+          debug my_int => _1;
+      }
+
+      bb0: {
+          StorageLive(_1);
+          _1 = const <T as MyTrait>::ASSOC_INT;
+          _0 = const ();
+          StorageDead(_1);
+          return;
+      }
+  }
+