Rollup merge of rust-lang#133870 - nbdd0121:asm, r=traviscross,nnethercote

Stabilize `asm_goto` feature gate

Stabilize `asm_goto` feature (tracked by rust-lang#119364). The issue will remain open and be updated to track `asm_goto_with_outputs`.

Reference PR: rust-lang/reference#1693

# Stabilization Report

This feature adds a `label <block>` operand type to `asm!`. `<block>` must be a block expression with type unit or never. The address of the block is substituted and the assembly may jump to the block. When block completes the `asm!` block returns and continues execution.

The block starts a new safety context and unsafe operations within must have additional `unsafe`s; the effect of `unsafe` that surrounds `asm!` block is cancelled. See rust-lang#119364 (comment) and rust-lang#131544.

It's currently forbidden to use `asm_goto` with output operands; that is still unstable under `asm_goto_with_outputs`.

Example:

```rust
unsafe {
    asm!(
        "jmp {}",
        label {
            println!("Jumped from asm!");
        }
    );
}
```

Tests:
- tests/ui/asm/x86_64/goto.rs
- tests/ui/asm/x86_64/goto-block-safe.stderr
- tests/ui/asm/x86_64/bad-options.rs
- tests/codegen/asm/goto.rs

Author: matthiaskrgr

compiler/rustc_ast_lowering/messages.ftl

@@ -185,8 +185,6 @@ ast_lowering_underscore_expr_lhs_assign =
 ast_lowering_unstable_inline_assembly = inline assembly is not stable yet on this architecture
 ast_lowering_unstable_inline_assembly_label_operand_with_outputs =
     using both label and output operands for inline assembly is unstable
-ast_lowering_unstable_inline_assembly_label_operands =
-    label operands for inline assembly are unstable
 ast_lowering_unstable_may_unwind = the `may_unwind` option is unstable
 
 ast_lowering_use_angle_brackets = use angle brackets instead

compiler/rustc_ast_lowering/src/asm.rs

@@ -470,22 +470,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             }
         }
 
-        // Feature gate checking for asm goto.
+        // Feature gate checking for `asm_goto_with_outputs`.
         if let Some((_, op_sp)) =
             operands.iter().find(|(op, _)| matches!(op, hir::InlineAsmOperand::Label { .. }))
         {
-            if !self.tcx.features().asm_goto() {
-                feature_err(
-                    sess,
-                    sym::asm_goto,
-                    *op_sp,
-                    fluent::ast_lowering_unstable_inline_assembly_label_operands,
-                )
-                .emit();
-            }
-
-            // In addition, check if an output operand is used.
-            // This is gated behind an additional feature.
+            // Check if an output operand is used.
             let output_operand_used = operands.iter().any(|(op, _)| {
                 matches!(
                     op,

compiler/rustc_feature/src/accepted.rs

@@ -62,6 +62,8 @@ declare_features! (
     (accepted, arbitrary_enum_discriminant, "1.66.0", Some(60553)),
     /// Allows using `const` operands in inline assembly.
     (accepted, asm_const, "1.82.0", Some(93332)),
+    /// Allows using `label` operands in inline assembly.
+    (accepted, asm_goto, "CURRENT_RUSTC_VERSION", Some(119364)),
     /// Allows using `sym` operands in inline assembly.
     (accepted, asm_sym, "1.66.0", Some(93333)),
     /// Allows the definition of associated constants in `trait` or `impl` blocks.

compiler/rustc_feature/src/unstable.rs

@@ -372,8 +372,6 @@ declare_features! (
     (unstable, asm_experimental_arch, "1.58.0", Some(93335)),
     /// Enables experimental register support in inline assembly.
     (unstable, asm_experimental_reg, "1.85.0", Some(133416)),
-    /// Allows using `label` operands in inline assembly.
-    (unstable, asm_goto, "1.78.0", Some(119364)),
     /// Allows using `label` operands in inline assembly together with output operands.
     (unstable, asm_goto_with_outputs, "1.85.0", Some(119364)),
     /// Allows the `may_unwind` option in inline assembly.

src/doc/unstable-book/src/language-features/asm-goto-with-outputs.md

@@ -0,0 +1,27 @@
+# `asm_goto_with_outputs`
+
+The tracking issue for this feature is: [#119364]
+
+[#119364]: https://github.com/rust-lang/rust/issues/119364
+
+------------------------
+
+This feature allows label operands to be used together with output operands.
+
+Example:
+```rust,ignore (partial-example, x86-only)
+
+unsafe {
+    let a: usize;
+    asm!(
+        "mov {}, 1"
+        "jmp {}",
+        out(reg) a,
+        label {
+            println!("Jumped from asm {}!", a);
+        }
+    );
+}
+```
+
+The output operands are assigned before the label blocks are executed.

src/doc/unstable-book/src/language-features/asm-goto.md

@@ -2,7 +2,7 @@
 //@ only-x86_64
 
 #![crate_type = "rlib"]
-#![feature(asm_goto, asm_goto_with_outputs)]
+#![feature(asm_goto_with_outputs)]
 
 use std::arch::asm;
 

tests/codegen/asm/goto.rs

@@ -1,6 +1,6 @@
 //@ only-x86_64
 
-#![feature(asm_unwind, asm_goto)]
+#![feature(asm_unwind)]
 
 use std::arch::{asm, global_asm};
 

tests/ui/asm/x86_64/bad-options.rs

@@ -2,7 +2,6 @@
 //@ needs-asm-support
 
 #![deny(unreachable_code)]
-#![feature(asm_goto)]
 
 use std::arch::asm;
 

tests/ui/asm/x86_64/goto-block-safe.rs

@@ -1,5 +1,5 @@
 error[E0133]: call to unsafe function `unreachable_unchecked` is unsafe and requires unsafe function or block
-  --> $DIR/goto-block-safe.rs:14:17
+  --> $DIR/goto-block-safe.rs:13:17
    |
 LL |     unsafe {
    |     ------ items do not inherit unsafety from separate enclosing items