Use more slice patterns inside the compiler

4 files changed, 14 insertions, 16 deletions

diff --git a/compiler/rustc_mir_transform/src/coverage/graph.rs b/compiler/rustc_mir_transform/src/coverage/graph.rs
index c3f4bbf1a65..31b20775194 100644
--- a/compiler/rustc_mir_transform/src/coverage/graph.rs
+++ b/compiler/rustc_mir_transform/src/coverage/graph.rs
@@ -350,8 +350,8 @@ fn bcb_filtered_successors<'a, 'tcx>(terminator: &'a Terminator<'tcx>) -> Covera
         // An inline asm terminator can normally be chained, except when it diverges or uses asm
         // goto.
         InlineAsm { ref targets, .. } => {
-            if targets.len() == 1 {
-                CoverageSuccessors::Chainable(targets[0])
+            if let [target] = targets[..] {
+                CoverageSuccessors::Chainable(target)
             } else {
                 CoverageSuccessors::NotChainable(targets)
             }
diff --git a/compiler/rustc_mir_transform/src/early_otherwise_branch.rs b/compiler/rustc_mir_transform/src/early_otherwise_branch.rs
index e4fec786814..49e41c35f1f 100644
--- a/compiler/rustc_mir_transform/src/early_otherwise_branch.rs
+++ b/compiler/rustc_mir_transform/src/early_otherwise_branch.rs
@@ -309,11 +309,11 @@ fn verify_candidate_branch<'tcx>(
 ) -> bool {
     // In order for the optimization to be correct, the branch must...
     // ...have exactly one statement
-    if branch.statements.len() != 1 {
+    let [statement] = branch.statements.as_slice() else {
         return false;
-    }
+    };
     // ...assign the discriminant of `place` in that statement
-    let StatementKind::Assign(boxed) = &branch.statements[0].kind else { return false };
+    let StatementKind::Assign(boxed) = &statement.kind else { return false };
     let (discr_place, Rvalue::Discriminant(from_place)) = &**boxed else { return false };
     if *from_place != place {
         return false;
diff --git a/compiler/rustc_mir_transform/src/instsimplify.rs b/compiler/rustc_mir_transform/src/instsimplify.rs
index 2fc5f7e536b..1589653968c 100644
--- a/compiler/rustc_mir_transform/src/instsimplify.rs
+++ b/compiler/rustc_mir_transform/src/instsimplify.rs
@@ -264,9 +264,7 @@ impl<'tcx> InstSimplifyContext<'tcx, '_> {
         };
 
         // It's definitely not a clone if there are multiple arguments
-        if args.len() != 1 {
-            return;
-        }
+        let [arg] = &args[..] else { return };
 
         let Some(destination_block) = *target else { return };
 
@@ -280,7 +278,7 @@ impl<'tcx> InstSimplifyContext<'tcx, '_> {
 
         // These types are easily available from locals, so check that before
         // doing DefId lookups to figure out what we're actually calling.
-        let arg_ty = args[0].node.ty(self.local_decls, self.tcx);
+        let arg_ty = arg.node.ty(self.local_decls, self.tcx);
 
         let ty::Ref(_region, inner_ty, Mutability::Not) = *arg_ty.kind() else { return };
 
diff --git a/compiler/rustc_mir_transform/src/validate.rs b/compiler/rustc_mir_transform/src/validate.rs
index 746d423b7a9..491ae1c0d08 100644
--- a/compiler/rustc_mir_transform/src/validate.rs
+++ b/compiler/rustc_mir_transform/src/validate.rs
@@ -898,8 +898,8 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                         self.param_env,
                         adt_def.non_enum_variant().fields[field].ty(self.tcx, args),
                     );
-                    if fields.len() == 1 {
-                        let src_ty = fields.raw[0].ty(self.body, self.tcx);
+                    if let [field] = fields.raw.as_slice() {
+                        let src_ty = field.ty(self.body, self.tcx);
                         if !self.mir_assign_valid_types(src_ty, dest_ty) {
                             self.fail(location, "union field has the wrong type");
                         }
@@ -967,11 +967,9 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                         self.fail(location, "RawPtr should be in runtime MIR only");
                     }
 
-                    if fields.len() != 2 {
-                        self.fail(location, "raw pointer aggregate must have 2 fields");
-                    } else {
-                        let data_ptr_ty = fields.raw[0].ty(self.body, self.tcx);
-                        let metadata_ty = fields.raw[1].ty(self.body, self.tcx);
+                    if let [data_ptr, metadata] = fields.raw.as_slice() {
+                        let data_ptr_ty = data_ptr.ty(self.body, self.tcx);
+                        let metadata_ty = metadata.ty(self.body, self.tcx);
                         if let ty::RawPtr(in_pointee, in_mut) = data_ptr_ty.kind() {
                             if *in_mut != mutability {
                                 self.fail(location, "input and output mutability must match");
@@ -998,6 +996,8 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                                 self.fail(location, "metadata for pointer-to-thin must be unit");
                             }
                         }
+                    } else {
+                        self.fail(location, "raw pointer aggregate must have 2 fields");
                     }
                 }
             },