Lower bindings in a predictable order

2024-02-28 00:34:33 +01:00 · 2024-02-28 00:34:33 +01:00 · 00497ad24b
commit 00497ad24b
parent 97bfa106c7
8 changed files with 66 additions and 96 deletions
--- a/compiler/rustc_mir_build/src/build/matches/simplify.rs
+++ b/compiler/rustc_mir_build/src/build/matches/simplify.rs
@ -43,60 +43,30 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
        //     let y = x;
        // }
        //
-        // We can't just reverse the binding order, because we must preserve pattern-order
-        // otherwise, e.g. in `let (Some(a), Some(b)) = (x, y)`. Our rule then is: deepest-first,
-        // and bindings at the same depth stay in source order.
-        //
-        // To do this, every time around the loop we prepend the newly found bindings to the
-        // bindings we already had.
-        //
-        // example:
-        // candidate.bindings = [1, 2, 3]
-        // bindings in iter 1: [4, 5]
-        // bindings in iter 2: [6, 7]
-        //
-        // final bindings: [6, 7, 4, 5, 1, 2, 3]
-        let mut accumulated_bindings = mem::take(candidate_bindings);
-        let mut simplified_match_pairs = Vec::new();
-        // Repeatedly simplify match pairs until we're left with only unsimplifiable ones.
-        loop {
-            for mut match_pair in mem::take(match_pairs) {
-                if let TestCase::Irrefutable { binding, ascription } = match_pair.test_case {
-                    if let Some(binding) = binding {
-                        candidate_bindings.push(binding);
-                    }
-                    if let Some(ascription) = ascription {
-                        candidate_ascriptions.push(ascription);
-                    }
-                    // Simplifiable pattern; we replace it with its subpairs and simplify further.
-                    match_pairs.append(&mut match_pair.subpairs);
-                } else {
-                    // Unsimplifiable pattern; we recursively simplify its subpairs and don't
-                    // process it further.
-                    self.simplify_match_pairs(
-                        &mut match_pair.subpairs,
-                        candidate_bindings,
-                        candidate_ascriptions,
-                    );
-                    simplified_match_pairs.push(match_pair);
+        // We therefore lower bindings from left-to-right, except we lower the `x` in `x @ pat`
+        // after any bindings in `pat`. This doesn't work for or-patterns: the current structure of
+        // match lowering forces us to lower bindings inside or-patterns last.
+        for mut match_pair in mem::take(match_pairs) {
+            self.simplify_match_pairs(
+                &mut match_pair.subpairs,
+                candidate_bindings,
+                candidate_ascriptions,
+            );
+            if let TestCase::Irrefutable { binding, ascription } = match_pair.test_case {
+                if let Some(binding) = binding {
+                    candidate_bindings.push(binding);
                }
-            }
-
-            // This does: accumulated_bindings = candidate.bindings.take() ++ accumulated_bindings
-            candidate_bindings.extend_from_slice(&accumulated_bindings);
-            mem::swap(candidate_bindings, &mut accumulated_bindings);
-            candidate_bindings.clear();
-
-            if match_pairs.is_empty() {
-                break;
+                if let Some(ascription) = ascription {
+                    candidate_ascriptions.push(ascription);
+                }
+                // Simplifiable pattern; we replace it with its already simplified subpairs.
+                match_pairs.append(&mut match_pair.subpairs);
+            } else {
+                // Unsimplifiable pattern; we keep it.
+                match_pairs.push(match_pair);
            }
        }

-        // Store computed bindings back in `candidate_bindings`.
-        mem::swap(candidate_bindings, &mut accumulated_bindings);
-        // Store simplified match pairs back in `match_pairs`.
-        mem::swap(match_pairs, &mut simplified_match_pairs);
-
        // Move or-patterns to the end, because they can result in us
        // creating additional candidates, so we want to test them as
        // late as possible.
--- a/tests/mir-opt/early_otherwise_branch.opt1.EarlyOtherwiseBranch.diff
+++ b/tests/mir-opt/early_otherwise_branch.opt1.EarlyOtherwiseBranch.diff
@ -51,13 +51,13 @@
 -     }
 - 
 -     bb3: {
-          StorageLive(_9);
-          _9 = (((_3.1: std::option::Option<u32>) as Some).0: u32);
          StorageLive(_8);
          _8 = (((_3.0: std::option::Option<u32>) as Some).0: u32);
+          StorageLive(_9);
+          _9 = (((_3.1: std::option::Option<u32>) as Some).0: u32);
          _0 = const 0_u32;
-          StorageDead(_8);
          StorageDead(_9);
+          StorageDead(_8);
 -         goto -> bb4;
 +         goto -> bb3;
      }
--- a/tests/mir-opt/early_otherwise_branch.opt2.EarlyOtherwiseBranch.diff
+++ b/tests/mir-opt/early_otherwise_branch.opt2.EarlyOtherwiseBranch.diff
@ -57,13 +57,13 @@
 -     }
 - 
 -     bb4: {
-          StorageLive(_10);
-          _10 = (((_3.1: std::option::Option<u32>) as Some).0: u32);
          StorageLive(_9);
          _9 = (((_3.0: std::option::Option<u32>) as Some).0: u32);
+          StorageLive(_10);
+          _10 = (((_3.1: std::option::Option<u32>) as Some).0: u32);
          _0 = const 0_u32;
-          StorageDead(_9);
          StorageDead(_10);
+          StorageDead(_9);
 -         goto -> bb6;
 +         goto -> bb4;
      }
--- a/tests/mir-opt/early_otherwise_branch.opt3.EarlyOtherwiseBranch.diff
+++ b/tests/mir-opt/early_otherwise_branch.opt3.EarlyOtherwiseBranch.diff
@ -51,13 +51,13 @@
 -     }
 - 
 -     bb3: {
-          StorageLive(_9);
-          _9 = (((_3.1: std::option::Option<bool>) as Some).0: bool);
          StorageLive(_8);
          _8 = (((_3.0: std::option::Option<u32>) as Some).0: u32);
+          StorageLive(_9);
+          _9 = (((_3.1: std::option::Option<bool>) as Some).0: bool);
          _0 = const 0_u32;
-          StorageDead(_8);
          StorageDead(_9);
+          StorageDead(_8);
 -         goto -> bb4;
 +         goto -> bb3;
      }
--- a/tests/mir-opt/early_otherwise_branch_3_element_tuple.opt1.EarlyOtherwiseBranch.diff
+++ b/tests/mir-opt/early_otherwise_branch_3_element_tuple.opt1.EarlyOtherwiseBranch.diff
@ -69,16 +69,16 @@
  
 -     bb4: {
 +     bb3: {
-          StorageLive(_13);
-          _13 = (((_4.2: std::option::Option<u32>) as Some).0: u32);
-          StorageLive(_12);
-          _12 = (((_4.1: std::option::Option<u32>) as Some).0: u32);
          StorageLive(_11);
          _11 = (((_4.0: std::option::Option<u32>) as Some).0: u32);
+          StorageLive(_12);
+          _12 = (((_4.1: std::option::Option<u32>) as Some).0: u32);
+          StorageLive(_13);
+          _13 = (((_4.2: std::option::Option<u32>) as Some).0: u32);
          _0 = const 0_u32;
-          StorageDead(_11);
-          StorageDead(_12);
          StorageDead(_13);
+          StorageDead(_12);
+          StorageDead(_11);
 -         goto -> bb5;
 +         goto -> bb4;
      }
--- a/tests/mir-opt/early_otherwise_branch_68867.try_sum.EarlyOtherwiseBranch.diff
+++ b/tests/mir-opt/early_otherwise_branch_68867.try_sum.EarlyOtherwiseBranch.diff
@ -116,12 +116,12 @@
      }
  
      bb6: {
-          StorageLive(_13);
-          _39 = deref_copy (_4.1: &ViewportPercentageLength);
-          _13 = (((*_39) as Vw).0: f32);
          StorageLive(_12);
-          _40 = deref_copy (_4.0: &ViewportPercentageLength);
-          _12 = (((*_40) as Vw).0: f32);
+          _39 = deref_copy (_4.0: &ViewportPercentageLength);
+          _12 = (((*_39) as Vw).0: f32);
+          StorageLive(_13);
+          _40 = deref_copy (_4.1: &ViewportPercentageLength);
+          _13 = (((*_40) as Vw).0: f32);
          StorageLive(_14);
          StorageLive(_15);
          _15 = _12;
@ -132,18 +132,18 @@
          StorageDead(_15);
          _3 = ViewportPercentageLength::Vw(move _14);
          StorageDead(_14);
-          StorageDead(_12);
          StorageDead(_13);
+          StorageDead(_12);
          goto -> bb10;
      }
  
      bb7: {
-          StorageLive(_18);
-          _41 = deref_copy (_4.1: &ViewportPercentageLength);
-          _18 = (((*_41) as Vh).0: f32);
          StorageLive(_17);
-          _42 = deref_copy (_4.0: &ViewportPercentageLength);
-          _17 = (((*_42) as Vh).0: f32);
+          _41 = deref_copy (_4.0: &ViewportPercentageLength);
+          _17 = (((*_41) as Vh).0: f32);
+          StorageLive(_18);
+          _42 = deref_copy (_4.1: &ViewportPercentageLength);
+          _18 = (((*_42) as Vh).0: f32);
          StorageLive(_19);
          StorageLive(_20);
          _20 = _17;
@ -154,18 +154,18 @@
          StorageDead(_20);
          _3 = ViewportPercentageLength::Vh(move _19);
          StorageDead(_19);
-          StorageDead(_17);
          StorageDead(_18);
+          StorageDead(_17);
          goto -> bb10;
      }
  
      bb8: {
-          StorageLive(_23);
-          _43 = deref_copy (_4.1: &ViewportPercentageLength);
-          _23 = (((*_43) as Vmin).0: f32);
          StorageLive(_22);
-          _44 = deref_copy (_4.0: &ViewportPercentageLength);
-          _22 = (((*_44) as Vmin).0: f32);
+          _43 = deref_copy (_4.0: &ViewportPercentageLength);
+          _22 = (((*_43) as Vmin).0: f32);
+          StorageLive(_23);
+          _44 = deref_copy (_4.1: &ViewportPercentageLength);
+          _23 = (((*_44) as Vmin).0: f32);
          StorageLive(_24);
          StorageLive(_25);
          _25 = _22;
@ -176,18 +176,18 @@
          StorageDead(_25);
          _3 = ViewportPercentageLength::Vmin(move _24);
          StorageDead(_24);
-          StorageDead(_22);
          StorageDead(_23);
+          StorageDead(_22);
          goto -> bb10;
      }
  
      bb9: {
-          StorageLive(_28);
-          _45 = deref_copy (_4.1: &ViewportPercentageLength);
-          _28 = (((*_45) as Vmax).0: f32);
          StorageLive(_27);
-          _46 = deref_copy (_4.0: &ViewportPercentageLength);
-          _27 = (((*_46) as Vmax).0: f32);
+          _45 = deref_copy (_4.0: &ViewportPercentageLength);
+          _27 = (((*_45) as Vmax).0: f32);
+          StorageLive(_28);
+          _46 = deref_copy (_4.1: &ViewportPercentageLength);
+          _28 = (((*_46) as Vmax).0: f32);
          StorageLive(_29);
          StorageLive(_30);
          _30 = _27;
@ -198,8 +198,8 @@
          StorageDead(_30);
          _3 = ViewportPercentageLength::Vmax(move _29);
          StorageDead(_29);
-          StorageDead(_27);
          StorageDead(_28);
+          StorageDead(_27);
          goto -> bb10;
      }
  
--- a/tests/mir-opt/early_otherwise_branch_noopt.noopt1.EarlyOtherwiseBranch.diff
+++ b/tests/mir-opt/early_otherwise_branch_noopt.noopt1.EarlyOtherwiseBranch.diff
@ -59,13 +59,13 @@
      }
  
      bb5: {
-          StorageLive(_10);
-          _10 = (((_3.1: std::option::Option<u32>) as Some).0: u32);
          StorageLive(_9);
          _9 = (((_3.0: std::option::Option<u32>) as Some).0: u32);
+          StorageLive(_10);
+          _10 = (((_3.1: std::option::Option<u32>) as Some).0: u32);
          _0 = const 0_u32;
-          StorageDead(_9);
          StorageDead(_10);
+          StorageDead(_9);
          goto -> bb8;
      }
  
--- a/tests/mir-opt/exponential_or.match_tuple.SimplifyCfg-initial.after.mir
+++ b/tests/mir-opt/exponential_or.match_tuple.SimplifyCfg-initial.after.mir
@ -19,8 +19,7 @@ fn match_tuple(_1: (u32, bool, Option<i32>, u32)) -> u32 {

    bb0: {
        PlaceMention(_1);
-        _2 = discriminant((_1.2: std::option::Option<i32>));
-        switchInt(move _2) -> [0: bb3, 1: bb2, otherwise: bb1];
+        switchInt((_1.0: u32)) -> [1: bb2, 4: bb2, otherwise: bb1];
    }

    bb1: {
@ -29,11 +28,12 @@ fn match_tuple(_1: (u32, bool, Option<i32>, u32)) -> u32 {
    }

    bb2: {
-        switchInt((((_1.2: std::option::Option<i32>) as Some).0: i32)) -> [1: bb3, 8: bb3, otherwise: bb1];
+        _2 = discriminant((_1.2: std::option::Option<i32>));
+        switchInt(move _2) -> [0: bb4, 1: bb3, otherwise: bb1];
    }

    bb3: {
-        switchInt((_1.0: u32)) -> [1: bb4, 4: bb4, otherwise: bb1];
+        switchInt((((_1.2: std::option::Option<i32>) as Some).0: i32)) -> [1: bb4, 8: bb4, otherwise: bb1];
    }

    bb4: {