Rollup merge of #119365 - nbdd0121:asm-goto, r=Amanieu

Add asm goto support to `asm!`

Tracking issue: #119364

This PR implements asm-goto support, using the syntax described in "future possibilities" section of [RFC2873](https://rust-lang.github.io/rfcs/2873-inline-asm.html#asm-goto).

Currently I have only implemented the `label` part, not the `fallthrough` part (i.e. fallthrough is implicit). This doesn't reduce the expressive though, since you can use label-break to get arbitrary control flow or simply set a value and rely on jump threading optimisation to get the desired control flow. I can add that later if deemed necessary.

r? ``@Amanieu``
cc ``@ojeda``

1 files changed, 5 insertions, 3 deletions

diff --git a/compiler/rustc_smir/src/rustc_smir/convert/mir.rs b/compiler/rustc_smir/src/rustc_smir/convert/mir.rs
index 501d6f7d304..003a9a59200 100644
--- a/compiler/rustc_smir/src/rustc_smir/convert/mir.rs
+++ b/compiler/rustc_smir/src/rustc_smir/convert/mir.rs
@@ -559,7 +559,8 @@ impl<'tcx> Stable<'tcx> for mir::InlineAsmOperand<'tcx> {
             }
             InlineAsmOperand::Const { .. }
             | InlineAsmOperand::SymFn { .. }
-            | InlineAsmOperand::SymStatic { .. } => (None, None),
+            | InlineAsmOperand::SymStatic { .. }
+            | InlineAsmOperand::Label { .. } => (None, None),
         };
 
         stable_mir::mir::InlineAsmOperand { in_value, out_place, raw_rpr: format!("{self:?}") }
@@ -632,14 +633,15 @@ impl<'tcx> Stable<'tcx> for mir::TerminatorKind<'tcx> {
                 operands,
                 options,
                 line_spans,
-                destination,
+                targets,
                 unwind,
             } => TerminatorKind::InlineAsm {
                 template: format!("{template:?}"),
                 operands: operands.iter().map(|operand| operand.stable(tables)).collect(),
                 options: format!("{options:?}"),
                 line_spans: format!("{line_spans:?}"),
-                destination: destination.map(|d| d.as_usize()),
+                // FIXME: Figure out how to do labels in SMIR
+                destination: targets.first().map(|d| d.as_usize()),
                 unwind: unwind.stable(tables),
             },
             mir::TerminatorKind::Yield { .. }