enable a few more tests in Miri and update the comment for others

Author: RalfJung

src/liballoc/tests/vec.rs

@@ -761,7 +761,6 @@ fn from_into_inner() {
     it.next().unwrap();
     let vec = it.collect::<Vec<_>>();
     assert_eq!(vec, [2, 3]);
-    #[cfg(not(miri))] // Miri does not support comparing dangling pointers
     assert!(ptr != vec.as_ptr());
 }
 

src/libcore/tests/fmt/mod.rs

@@ -3,7 +3,6 @@ mod float;
 mod num;
 
 #[test]
-#[cfg(not(miri))] // Miri cannot print pointers
 fn test_format_flags() {
     // No residual flags left by pointer formatting
     let p = "".as_ptr();
@@ -13,7 +12,6 @@ fn test_format_flags() {
 }
 
 #[test]
-#[cfg(not(miri))] // Miri cannot print pointers
 fn test_pointer_formats_data_pointer() {
     let b: &[u8] = b"";
     let s: &str = "";

src/libcore/tests/ptr.rs

@@ -253,7 +253,6 @@ fn test_unsized_nonnull() {
 
 #[test]
 #[allow(warnings)]
-#[cfg(not(miri))] // Miri cannot hash pointers
 // Have a symbol for the test below. It doesn’t need to be an actual variadic function, match the
 // ABI, or even point to an actual executable code, because the function itself is never invoked.
 #[no_mangle]
@@ -293,7 +292,7 @@ fn write_unaligned_drop() {
 }
 
 #[test]
-#[cfg(not(miri))] // Miri cannot compute actual alignment of an allocation
+#[cfg(not(miri))] // Miri does not compute a maximal `mid` for `align_offset`
 fn align_offset_zst() {
     // For pointers of stride = 0, the pointer is already aligned or it cannot be aligned at
     // all, because no amount of elements will align the pointer.
@@ -308,7 +307,7 @@ fn align_offset_zst() {
 }
 
 #[test]
-#[cfg(not(miri))] // Miri cannot compute actual alignment of an allocation
+#[cfg(not(miri))] // Miri does not compute a maximal `mid` for `align_offset`
 fn align_offset_stride1() {
     // For pointers of stride = 1, the pointer can always be aligned. The offset is equal to
     // number of bytes.

src/libcore/tests/slice.rs

@@ -1396,7 +1396,7 @@ pub mod memchr {
 }
 
 #[test]
-#[cfg(not(miri))] // Miri cannot compute actual alignment of an allocation
+#[cfg(not(miri))] // Miri does not compute a maximal `mid` for `align_offset`
 fn test_align_to_simple() {
     let bytes = [1u8, 2, 3, 4, 5, 6, 7];
     let (prefix, aligned, suffix) = unsafe { bytes.align_to::<u16>() };
@@ -1420,7 +1420,7 @@ fn test_align_to_zst() {
 }
 
 #[test]
-#[cfg(not(miri))] // Miri cannot compute actual alignment of an allocation
+#[cfg(not(miri))] // Miri does not compute a maximal `mid` for `align_offset`
 fn test_align_to_non_trivial() {
     #[repr(align(8))] struct U64(u64, u64);
     #[repr(align(8))] struct U64U64U32(u64, u64, u32);