Auto merge of #116583 - saethlin:inline-small-core-fns, r=<try>

Add #[inline] to small functions in core

Where "small" is strictly defined as optimized_mir with 5 or less statements and no calls. I've also applied that heuristic recursively; applying it once causes some functions to become eligible for MIR inlining which brings other functions under the threshold.

r? `@ghost`

Author: bors

library/core/src/array/mod.rs

@@ -143,13 +143,15 @@ impl fmt::Display for TryFromSliceError {
 #[stable(feature = "try_from", since = "1.34.0")]
 impl Error for TryFromSliceError {
     #[allow(deprecated)]
+    #[inline]
     fn description(&self) -> &str {
         "could not convert slice to array"
     }
 }
 
 #[stable(feature = "try_from_slice_error", since = "1.36.0")]
 impl From<Infallible> for TryFromSliceError {
+    #[inline]
     fn from(x: Infallible) -> TryFromSliceError {
         match x {}
     }

library/core/src/char/convert.rs

@@ -190,6 +190,7 @@ enum CharErrorKind {
 #[stable(feature = "char_from_str", since = "1.20.0")]
 impl Error for ParseCharError {
     #[allow(deprecated)]
+    #[inline]
     fn description(&self) -> &str {
         match self.kind {
             CharErrorKind::EmptyString => "cannot parse char from empty string",

library/core/src/char/decode.rs

@@ -109,6 +109,7 @@ impl DecodeUtf16Error {
     /// Returns the unpaired surrogate which caused this error.
     #[must_use]
     #[stable(feature = "decode_utf16", since = "1.9.0")]
+    #[inline]
     pub fn unpaired_surrogate(&self) -> u16 {
         self.code
     }
@@ -124,6 +125,7 @@ impl fmt::Display for DecodeUtf16Error {
 #[stable(feature = "decode_utf16", since = "1.9.0")]
 impl Error for DecodeUtf16Error {
     #[allow(deprecated)]
+    #[inline]
     fn description(&self) -> &str {
         "unpaired surrogate found"
     }

library/core/src/char/mod.rs

@@ -229,6 +229,7 @@ impl EscapeDefault {
         Self(escape::EscapeIterInner::from_array(data))
     }
 
+    #[inline]
     fn from_unicode(esc: EscapeUnicode) -> Self {
         Self(esc.0)
     }
@@ -304,6 +305,7 @@ enum EscapeDebugInner {
 }
 
 impl EscapeDebug {
+    #[inline]
     fn printable(chr: char) -> Self {
         Self(EscapeDebugInner::Char(chr))
     }
@@ -314,6 +316,7 @@ impl EscapeDebug {
         Self(EscapeDebugInner::Bytes(iter))
     }
 
+    #[inline]
     fn from_unicode(esc: EscapeUnicode) -> Self {
         Self(EscapeDebugInner::Bytes(esc.0))
     }
@@ -339,6 +342,7 @@ impl Iterator for EscapeDebug {
         }
     }
 
+    #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         let n = self.len();
         (n, Some(n))
@@ -352,6 +356,7 @@ impl Iterator for EscapeDebug {
 
 #[stable(feature = "char_escape_debug", since = "1.20.0")]
 impl ExactSizeIterator for EscapeDebug {
+    #[inline]
     fn len(&self) -> usize {
         match &self.0 {
             EscapeDebugInner::Bytes(bytes) => bytes.len(),
@@ -389,6 +394,7 @@ impl Iterator for ToLowercase {
     fn next(&mut self) -> Option<char> {
         self.0.next()
     }
+    #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.0.size_hint()
     }
@@ -423,6 +429,7 @@ impl Iterator for ToUppercase {
     fn next(&mut self) -> Option<char> {
         self.0.next()
     }
+    #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.0.size_hint()
     }
@@ -450,6 +457,7 @@ enum CaseMappingIter {
 }
 
 impl CaseMappingIter {
+    #[inline]
     fn new(chars: [char; 3]) -> CaseMappingIter {
         if chars[2] == '\0' {
             if chars[1] == '\0' {
@@ -465,6 +473,7 @@ impl CaseMappingIter {
 
 impl Iterator for CaseMappingIter {
     type Item = char;
+    #[inline]
     fn next(&mut self) -> Option<char> {
         match *self {
             CaseMappingIter::Three(a, b, c) => {
@@ -483,6 +492,7 @@ impl Iterator for CaseMappingIter {
         }
     }
 
+    #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         let size = match self {
             CaseMappingIter::Three(..) => 3,
@@ -495,6 +505,7 @@ impl Iterator for CaseMappingIter {
 }
 
 impl DoubleEndedIterator for CaseMappingIter {
+    #[inline]
     fn next_back(&mut self) -> Option<char> {
         match *self {
             CaseMappingIter::Three(a, b, c) => {

library/core/src/convert/mod.rs

@@ -904,34 +904,39 @@ pub enum Infallible {}
 
 #[stable(feature = "convert_infallible", since = "1.34.0")]
 impl Clone for Infallible {
+    #[inline]
     fn clone(&self) -> Infallible {
         match *self {}
     }
 }
 
 #[stable(feature = "convert_infallible", since = "1.34.0")]
 impl fmt::Debug for Infallible {
+    #[inline]
     fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {}
     }
 }
 
 #[stable(feature = "convert_infallible", since = "1.34.0")]
 impl fmt::Display for Infallible {
+    #[inline]
     fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {}
     }
 }
 
 #[stable(feature = "str_parse_error2", since = "1.8.0")]
 impl Error for Infallible {
+    #[inline]
     fn description(&self) -> &str {
         match *self {}
     }
 }
 
 #[stable(feature = "convert_infallible", since = "1.34.0")]
 impl PartialEq for Infallible {
+    #[inline]
     fn eq(&self, _: &Infallible) -> bool {
         match *self {}
     }
@@ -942,13 +947,15 @@ impl Eq for Infallible {}
 
 #[stable(feature = "convert_infallible", since = "1.34.0")]
 impl PartialOrd for Infallible {
+    #[inline]
     fn partial_cmp(&self, _other: &Self) -> Option<crate::cmp::Ordering> {
         match *self {}
     }
 }
 
 #[stable(feature = "convert_infallible", since = "1.34.0")]
 impl Ord for Infallible {
+    #[inline]
     fn cmp(&self, _other: &Self) -> crate::cmp::Ordering {
         match *self {}
     }

library/core/src/error.rs

@@ -514,6 +514,7 @@ pub struct Request<'a>(dyn Erased<'a> + 'a);
 
 impl<'a> Request<'a> {
     /// Create a new `&mut Request` from a `&mut dyn Erased` trait object.
+    #[inline]
     fn new<'b>(erased: &'b mut (dyn Erased<'a> + 'a)) -> &'b mut Request<'a> {
         // SAFETY: transmuting `&mut (dyn Erased<'a> + 'a)` to `&mut Request<'a>` is safe since
         // `Request` is repr(transparent).
@@ -1046,6 +1047,7 @@ impl<'a, T: Error + ?Sized> Error for &'a T {
 #[stable(feature = "fmt_error", since = "1.11.0")]
 impl Error for crate::fmt::Error {
     #[allow(deprecated)]
+    #[inline]
     fn description(&self) -> &str {
         "an error occurred when formatting an argument"
     }
@@ -1054,6 +1056,7 @@ impl Error for crate::fmt::Error {
 #[stable(feature = "try_borrow", since = "1.13.0")]
 impl Error for crate::cell::BorrowError {
     #[allow(deprecated)]
+    #[inline]
     fn description(&self) -> &str {
         "already mutably borrowed"
     }
@@ -1062,6 +1065,7 @@ impl Error for crate::cell::BorrowError {
 #[stable(feature = "try_borrow", since = "1.13.0")]
 impl Error for crate::cell::BorrowMutError {
     #[allow(deprecated)]
+    #[inline]
     fn description(&self) -> &str {
         "already borrowed"
     }
@@ -1070,6 +1074,7 @@ impl Error for crate::cell::BorrowMutError {
 #[stable(feature = "try_from", since = "1.34.0")]
 impl Error for crate::char::CharTryFromError {
     #[allow(deprecated)]
+    #[inline]
     fn description(&self) -> &str {
         "converted integer out of range for `char`"
     }

library/core/src/ffi/c_str.rs

@@ -124,9 +124,11 @@ enum FromBytesWithNulErrorKind {
 }
 
 impl FromBytesWithNulError {
+    #[inline]
     const fn interior_nul(pos: usize) -> FromBytesWithNulError {
         FromBytesWithNulError { kind: FromBytesWithNulErrorKind::InteriorNul(pos) }
     }
+    #[inline]
     const fn not_nul_terminated() -> FromBytesWithNulError {
         FromBytesWithNulError { kind: FromBytesWithNulErrorKind::NotNulTerminated }
     }
@@ -135,6 +137,7 @@ impl FromBytesWithNulError {
 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
 impl Error for FromBytesWithNulError {
     #[allow(deprecated)]
+    #[inline]
     fn description(&self) -> &str {
         match self.kind {
             FromBytesWithNulErrorKind::InteriorNul(..) => {
@@ -695,6 +698,7 @@ impl AsRef<CStr> for CStr {
 /// located within `isize::MAX` from `ptr`.
 #[inline]
 const unsafe fn const_strlen(ptr: *const c_char) -> usize {
+    #[inline]
     const fn strlen_ct(s: *const c_char) -> usize {
         let mut len = 0;
 

library/core/src/ffi/mod.rs

@@ -612,6 +612,7 @@ impl<'f> Clone for VaListImpl<'f> {
     issue = "44930"
 )]
 impl<'f> Drop for VaListImpl<'f> {
+    #[inline]
     fn drop(&mut self) {
         // FIXME: this should call `va_end`, but there's no clean way to
         // guarantee that `drop` always gets inlined into its caller,

library/core/src/fmt/builders.rs

@@ -12,6 +12,7 @@ struct PadAdapterState {
 }
 
 impl Default for PadAdapterState {
+    #[inline]
     fn default() -> Self {
         PadAdapterState { on_newline: true }
     }

library/core/src/fmt/float.rs

@@ -13,6 +13,7 @@ trait GeneralFormat: PartialOrd {
 macro_rules! impl_general_format {
     ($($t:ident)*) => {
         $(impl GeneralFormat for $t {
+            #[inline]
             fn already_rounded_value_should_use_exponential(&self) -> bool {
                 let abs = $t::abs_private(*self);
                 (abs != 0.0 && abs < 1e-4) || abs >= 1e+16