Add documentation for asm!

Author: Amanieu

src/doc/unstable-book/src/library-features/asm.md

@@ -1293,30 +1293,29 @@ pub(crate) mod builtin {
     /// [unstable book]: ../unstable-book/library-features/asm.html
     #[unstable(
         feature = "asm",
-        issue = "70173",
+        issue = "72016",
         reason = "inline assembly is not stable enough for use and is subject to change"
     )]
     #[rustc_builtin_macro]
     #[macro_export]
     macro_rules! asm {
-        ("assembly template"
-                        : $("output"(operand),)*
-                        : $("input"(operand),)*
-                        : $("clobbers",)*
-                        : $("options",)*) => {
+        ("assembly template",
+            $(operands,)*
+            $(options($(option),*))?
+        ) => {
             /* compiler built-in */
         };
     }
 
-    /// Inline assembly.
+    /// LLVM-style inline assembly.
     ///
     /// Read the [unstable book] for the usage.
     ///
     /// [unstable book]: ../unstable-book/library-features/llvm-asm.html
     #[unstable(
         feature = "llvm_asm",
         issue = "70173",
-        reason = "inline assembly is not stable enough for use and is subject to change"
+        reason = "LLVM-style inline assembly will never be stabilized, prefer using asm! instead"
     )]
     #[rustc_builtin_macro]
     #[macro_export]

src/libcore/macros/mod.rs

@@ -7,6 +7,6 @@ llvm_asm!("nop" "nop");
 ```
 
 Considering that this would be a long explanation, we instead recommend you
-take a look at the [`asm`] chapter of the Unstable book:
+take a look at the [`llvm_asm`] chapter of the Unstable book:
 
-[asm]: https://doc.rust-lang.org/stable/unstable-book/library-features/asm.html
+[llvm_asm]: https://doc.rust-lang.org/stable/unstable-book/library-features/llvm-asm.html

src/librustc_error_codes/error_codes/E0660.md

@@ -8,6 +8,6 @@ llvm_asm!("nop" : "r"(a));
 ```
 
 Considering that this would be a long explanation, we instead recommend you
-take a look at the [`asm`] chapter of the Unstable book:
+take a look at the [`llvm_asm`] chapter of the Unstable book:
 
-[asm]: https://doc.rust-lang.org/stable/unstable-book/library-features/asm.html
+[llvm_asm]: https://doc.rust-lang.org/stable/unstable-book/library-features/llvm-asm.html

src/librustc_error_codes/error_codes/E0661.md

@@ -11,6 +11,6 @@ llvm_asm!("xor %eax, %eax"
 ```
 
 Considering that this would be a long explanation, we instead recommend you
-take a look at the [`asm`] chapter of the Unstable book:
+take a look at the [`llvm_asm`] chapter of the Unstable book:
 
-[asm]: https://doc.rust-lang.org/stable/unstable-book/library-features/asm.html
+[llvm_asm]: https://doc.rust-lang.org/stable/unstable-book/library-features/llvm-asm.html

src/librustc_error_codes/error_codes/E0662.md

@@ -11,6 +11,6 @@ llvm_asm!("xor %eax, %eax"
 ```
 
 Considering that this would be a long explanation, we instead recommend you
-take a look at the [`asm`] chapter of the Unstable book:
+take a look at the [`llvm_asm`] chapter of the Unstable book:
 
-[asm]: https://doc.rust-lang.org/stable/unstable-book/library-features/asm.html
+[llvm_asm]: https://doc.rust-lang.org/stable/unstable-book/library-features/llvm-asm.html

src/librustc_error_codes/error_codes/E0663.md

@@ -11,6 +11,6 @@ llvm_asm!("mov $$0x200, %eax"
 ```
 
 Considering that this would be a long explanation, we instead recommend you
-take a look at the [`asm`] chapter of the Unstable book:
+take a look at the [`llvm_asm`] chapter of the Unstable book:
 
-[asm]: https://doc.rust-lang.org/stable/unstable-book/library-features/asm.html
+[llvm_asm]: https://doc.rust-lang.org/stable/unstable-book/library-features/llvm-asm.html