Rollup merge of #67585 - ranma42:fix/char-is-ascii-codegen, r=Amanieu

Improve `char::is_ascii_*` codegen

This PR is an attempt to fix https://github.com/rust-lang/rust/issues/65127

A couple of warnings:
 1. the generated code might be further improved (in LLVM and/or MIR) by emitting better comparison sequences; in particular, this would improve the performance of "complex" checks such as those in `is_ascii_punctuation`
 2. the second commit is currently marked "DO NOT MERGE", because it regresses SIMD on `u8` slices; this could likely be fixed by improving the computation/usage of demanded bits in LLVM

An alternative approach to remove the code duplication might be the use of macros, but currently most of the duplication is actually in the doc comments, so maybe just keeping the redundancy could be ok

src/libcore/char/methods.rs

@@ -1075,7 +1075,10 @@ pub fn make_ascii_lowercase(&mut self) {
     #[rustc_const_unstable(feature = "const_ascii_ctype_on_intrinsics", issue = "68983")]
     #[inline]
     pub const fn is_ascii_alphabetic(&self) -> bool {
-        self.is_ascii() && (*self as u8).is_ascii_alphabetic()
+        match *self {
+            'A'..='Z' | 'a'..='z' => true,
+            _ => false,
+        }
     }
 
     /// Checks if the value is an ASCII uppercase character:
@@ -1108,7 +1111,10 @@ pub const fn is_ascii_alphabetic(&self) -> bool {
     #[rustc_const_unstable(feature = "const_ascii_ctype_on_intrinsics", issue = "68983")]
     #[inline]
     pub const fn is_ascii_uppercase(&self) -> bool {
-        self.is_ascii() && (*self as u8).is_ascii_uppercase()
+        match *self {
+            'A'..='Z' => true,
+            _ => false,
+        }
     }
 
     /// Checks if the value is an ASCII lowercase character:
@@ -1141,7 +1147,10 @@ pub const fn is_ascii_uppercase(&self) -> bool {
     #[rustc_const_unstable(feature = "const_ascii_ctype_on_intrinsics", issue = "68983")]
     #[inline]
     pub const fn is_ascii_lowercase(&self) -> bool {
-        self.is_ascii() && (*self as u8).is_ascii_lowercase()
+        match *self {
+            'a'..='z' => true,
+            _ => false,
+        }
     }
 
     /// Checks if the value is an ASCII alphanumeric character:
@@ -1177,7 +1186,10 @@ pub const fn is_ascii_lowercase(&self) -> bool {
     #[rustc_const_unstable(feature = "const_ascii_ctype_on_intrinsics", issue = "68983")]
     #[inline]
     pub const fn is_ascii_alphanumeric(&self) -> bool {
-        self.is_ascii() && (*self as u8).is_ascii_alphanumeric()
+        match *self {
+            '0'..='9' | 'A'..='Z' | 'a'..='z' => true,
+            _ => false,
+        }
     }
 
     /// Checks if the value is an ASCII decimal digit:
@@ -1210,7 +1222,10 @@ pub const fn is_ascii_alphanumeric(&self) -> bool {
     #[rustc_const_unstable(feature = "const_ascii_ctype_on_intrinsics", issue = "68983")]
     #[inline]
     pub const fn is_ascii_digit(&self) -> bool {
-        self.is_ascii() && (*self as u8).is_ascii_digit()
+        match *self {
+            '0'..='9' => true,
+            _ => false,
+        }
     }
 
     /// Checks if the value is an ASCII hexadecimal digit:
@@ -1246,7 +1261,10 @@ pub const fn is_ascii_digit(&self) -> bool {
     #[rustc_const_unstable(feature = "const_ascii_ctype_on_intrinsics", issue = "68983")]
     #[inline]
     pub const fn is_ascii_hexdigit(&self) -> bool {
-        self.is_ascii() && (*self as u8).is_ascii_hexdigit()
+        match *self {
+            '0'..='9' | 'A'..='F' | 'a'..='f' => true,
+            _ => false,
+        }
     }
 
     /// Checks if the value is an ASCII punctuation character:
@@ -1283,7 +1301,10 @@ pub const fn is_ascii_hexdigit(&self) -> bool {
     #[rustc_const_unstable(feature = "const_ascii_ctype_on_intrinsics", issue = "68983")]
     #[inline]
     pub const fn is_ascii_punctuation(&self) -> bool {
-        self.is_ascii() && (*self as u8).is_ascii_punctuation()
+        match *self {
+            '!'..='/' | ':'..='@' | '['..='`' | '{'..='~' => true,
+            _ => false,
+        }
     }
 
     /// Checks if the value is an ASCII graphic character:
@@ -1316,7 +1337,10 @@ pub const fn is_ascii_punctuation(&self) -> bool {
     #[rustc_const_unstable(feature = "const_ascii_ctype_on_intrinsics", issue = "68983")]
     #[inline]
     pub const fn is_ascii_graphic(&self) -> bool {
-        self.is_ascii() && (*self as u8).is_ascii_graphic()
+        match *self {
+            '!'..='~' => true,
+            _ => false,
+        }
     }
 
     /// Checks if the value is an ASCII whitespace character:
@@ -1366,7 +1390,10 @@ pub const fn is_ascii_graphic(&self) -> bool {
     #[rustc_const_unstable(feature = "const_ascii_ctype_on_intrinsics", issue = "68983")]
     #[inline]
     pub const fn is_ascii_whitespace(&self) -> bool {
-        self.is_ascii() && (*self as u8).is_ascii_whitespace()
+        match *self {
+            '\t' | '\n' | '\x0C' | '\r' | ' ' => true,
+            _ => false,
+        }
     }
 
     /// Checks if the value is an ASCII control character:
@@ -1401,6 +1428,9 @@ pub const fn is_ascii_whitespace(&self) -> bool {
     #[rustc_const_unstable(feature = "const_ascii_ctype_on_intrinsics", issue = "68983")]
     #[inline]
     pub const fn is_ascii_control(&self) -> bool {
-        self.is_ascii() && (*self as u8).is_ascii_control()
+        match *self {
+            '\0'..='\x1F' | '\x7F' => true,
+            _ => false,
+        }
     }
 }