Add some regression tests

src/test/ui/const-generics/issues/issue-75299.rs

@@ -0,0 +1,11 @@
+// compile-flags: -Zmir-opt-level=3
+// run-pass
+
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+fn main() {
+    fn foo<const N: usize>() -> [u8; N] {
+        [0; N]
+    }
+    let _x = foo::<1>();
+}

src/test/ui/issues/issue-68951.rs

@@ -0,0 +1,9 @@
+// check-pass
+
+fn main() {
+    let array = [0x42u8; 10];
+    for b in &array {
+        let lo = b & 0xf;
+        let hi = (b >> 4) & 0xf;
+    }
+}

src/test/ui/pattern/issue-66501.rs

@@ -0,0 +1,12 @@
+// check-pass
+
+#![allow(unreachable_patterns)]
+
+fn main() {
+    const CONST: &[Option<()>; 1] = &[Some(())];
+    match &[Some(())] {
+        &[None] => {}
+        CONST => {}
+        &[Some(())] => {}
+    }
+}

src/test/ui/pattern/issue-72565.rs

@@ -0,0 +1,8 @@
+const F: &'static dyn PartialEq<u32> = &7u32;
+
+fn main() {
+    let a: &dyn PartialEq<u32> = &7u32;
+    match a {
+        F => panic!(), //~ ERROR: `&dyn PartialEq<u32>` cannot be used in patterns
+    }
+}

src/test/ui/pattern/issue-72565.stderr

@@ -0,0 +1,8 @@
+error: `&dyn PartialEq<u32>` cannot be used in patterns
+  --> $DIR/issue-72565.rs:6:9
+   |
+LL |         F => panic!(),
+   |         ^
+
+error: aborting due to previous error
+

src/test/ui/type-alias-impl-trait/issue-74244.rs

@@ -0,0 +1,20 @@
+#![feature(type_alias_impl_trait)]
+
+trait Allocator {
+    type Buffer;
+}
+
+struct DefaultAllocator;
+
+impl<T> Allocator for DefaultAllocator {
+    //~^ ERROR: the type parameter `T` is not constrained
+    type Buffer = ();
+}
+
+type A = impl Fn(<DefaultAllocator as Allocator>::Buffer);
+
+fn foo() -> A {
+    |_| ()
+}
+
+fn main() {}

src/test/ui/type-alias-impl-trait/issue-74244.stderr

@@ -0,0 +1,9 @@
+error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predicates
+  --> $DIR/issue-74244.rs:9:6
+   |
+LL | impl<T> Allocator for DefaultAllocator {
+   |      ^ unconstrained type parameter
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0207`.