Auto merge of #60730 - matthewjasper:optimize-false-edges, r=pnkfelix

Optimize matches

Attempt to fix or improve #60571

This is breaking some diagnostics because the MIR for match arms isn't in source order any more.

cc @Centril

src/librustc/mir/mod.rs

@@ -1196,9 +1196,9 @@ pub enum TerminatorKind<'tcx> {
     FalseEdges {
         /// The target normal control flow will take
         real_target: BasicBlock,
-        /// The list of blocks control flow could conceptually take, but won't
-        /// in practice
-        imaginary_targets: Vec<BasicBlock>,
+        /// A block control flow could conceptually jump to, but won't in
+        /// practice
+        imaginary_target: BasicBlock,
     },
     /// A terminator for blocks that only take one path in reality, but where we
     /// reserve the right to unwind in borrowck, even if it won't happen in practice.
@@ -1335,8 +1335,8 @@ impl<'tcx> TerminatorKind<'tcx> {
             SwitchInt { ref targets, .. } => None.into_iter().chain(&targets[..]),
             FalseEdges {
                 ref real_target,
-                ref imaginary_targets,
-            } => Some(real_target).into_iter().chain(&imaginary_targets[..]),
+                ref imaginary_target,
+            } => Some(real_target).into_iter().chain(slice::from_ref(imaginary_target)),
         }
     }
 
@@ -1422,10 +1422,10 @@ impl<'tcx> TerminatorKind<'tcx> {
             } => None.into_iter().chain(&mut targets[..]),
             FalseEdges {
                 ref mut real_target,
-                ref mut imaginary_targets,
+                ref mut imaginary_target,
             } => Some(real_target)
                 .into_iter()
-                .chain(&mut imaginary_targets[..]),
+                .chain(slice::from_mut(imaginary_target)),
         }
     }
 
@@ -1722,12 +1722,9 @@ impl<'tcx> TerminatorKind<'tcx> {
             Assert { cleanup: None, .. } => vec!["".into()],
             Assert { .. } => vec!["success".into(), "unwind".into()],
             FalseEdges {
-                ref imaginary_targets,
                 ..
             } => {
-                let mut l = vec!["real".into()];
-                l.resize(imaginary_targets.len() + 1, "imaginary".into());
-                l
+                vec!["real".into(), "imaginary".into()]
             }
             FalseUnwind {
                 unwind: Some(_), ..
@@ -3356,10 +3353,10 @@ impl<'tcx> TypeFoldable<'tcx> for Terminator<'tcx> {
             Unreachable => Unreachable,
             FalseEdges {
                 real_target,
-                ref imaginary_targets,
+                imaginary_target,
             } => FalseEdges {
                 real_target,
-                imaginary_targets: imaginary_targets.clone(),
+                imaginary_target,
             },
             FalseUnwind {
                 real_target,

src/librustc_mir/borrow_check/mod.rs

@@ -780,7 +780,7 @@ impl<'cx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx
             | TerminatorKind::Unreachable
             | TerminatorKind::FalseEdges {
                 real_target: _,
-                imaginary_targets: _,
+                imaginary_target: _,
             }
             | TerminatorKind::FalseUnwind {
                 real_target: _,

src/librustc_mir/borrow_check/nll/invalidation.rs

@@ -244,7 +244,7 @@ impl<'cx, 'tcx> Visitor<'tcx> for InvalidationGenerator<'cx, 'tcx> {
             | TerminatorKind::Unreachable
             | TerminatorKind::FalseEdges {
                 real_target: _,
-                imaginary_targets: _,
+                imaginary_target: _,
             }
             | TerminatorKind::FalseUnwind {
                 real_target: _,

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -1792,12 +1792,10 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             }
             TerminatorKind::FalseEdges {
                 real_target,
-                ref imaginary_targets,
+                imaginary_target,
             } => {
                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
-                for target in imaginary_targets {
-                    self.assert_iscleanup(body, block_data, *target, is_cleanup);
-                }
+                self.assert_iscleanup(body, block_data, imaginary_target, is_cleanup);
             }
             TerminatorKind::FalseUnwind {
                 real_target,