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

Improve `char::is_ascii_*` codegen

This PR is an attempt to fix rust-lang#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

Author: Dylan-DPC

src/libcore/char/methods.rs

@@ -1075,7 +1075,10 @@ impl char {
     #[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 @@ impl char {
     #[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 @@ impl char {
     #[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 @@ impl char {
     #[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 @@ impl char {
     #[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 @@ impl char {
     #[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 @@ impl char {
     #[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 @@ impl char {
     #[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 @@ impl char {
     #[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 @@ impl char {
     #[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,
+        }
     }
 }