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``

compiler/rustc_mir_dataflow/src/framework/direction.rs

@@ -242,9 +242,9 @@ impl Direction for Backward {
                     propagate(pred, &tmp);
                 }
 
-                mir::TerminatorKind::InlineAsm {
-                    destination: Some(dest), ref operands, ..
-                } if dest == bb => {
+                mir::TerminatorKind::InlineAsm { ref targets, ref operands, .. }
+                    if targets.contains(&bb) =>
+                {
                     let mut tmp = exit_state.clone();
                     analysis.apply_call_return_effect(
                         &mut tmp,
@@ -491,9 +491,12 @@ impl Direction for Forward {
                 if let Some(cleanup) = cleanup {
                     propagate(cleanup, exit_state);
                 }
-                if let Some(return_) = return_ {
+
+                if !return_.is_empty() {
                     analysis.apply_call_return_effect(exit_state, bb, place);
-                    propagate(return_, exit_state);
+                    for &target in return_ {
+                        propagate(target, exit_state);
+                    }
                 }
             }
             TerminatorEdges::SwitchInt { targets, discr } => {

compiler/rustc_mir_dataflow/src/framework/graphviz.rs

@@ -299,7 +299,9 @@ where
                 })?;
             }
 
-            mir::TerminatorKind::InlineAsm { destination: Some(_), ref operands, .. } => {
+            mir::TerminatorKind::InlineAsm { ref targets, ref operands, .. }
+                if !targets.is_empty() =>
+            {
                 self.write_row(w, "", "(on successful return)", |this, w, fmt| {
                     let state_on_unwind = this.results.get().clone();
                     this.results.apply_custom_effect(|analysis, state| {

compiler/rustc_mir_dataflow/src/impls/storage_liveness.rs

@@ -271,7 +271,8 @@ impl<'tcx> crate::GenKillAnalysis<'tcx> for MaybeRequiresStorage<'_, 'tcx> {
                         InlineAsmOperand::In { .. }
                         | InlineAsmOperand::Const { .. }
                         | InlineAsmOperand::SymFn { .. }
-                        | InlineAsmOperand::SymStatic { .. } => {}
+                        | InlineAsmOperand::SymStatic { .. }
+                        | InlineAsmOperand::Label { .. } => {}
                     }
                 }
             }

compiler/rustc_mir_dataflow/src/move_paths/builder.rs

@@ -491,7 +491,7 @@ impl<'b, 'a, 'tcx, F: Fn(Ty<'tcx>) -> bool> Gatherer<'b, 'a, 'tcx, F> {
                 ref operands,
                 options: _,
                 line_spans: _,
-                destination: _,
+                targets: _,
                 unwind: _,
             } => {
                 for op in operands {
@@ -515,7 +515,8 @@ impl<'b, 'a, 'tcx, F: Fn(Ty<'tcx>) -> bool> Gatherer<'b, 'a, 'tcx, F> {
                         }
                         InlineAsmOperand::Const { value: _ }
                         | InlineAsmOperand::SymFn { value: _ }
-                        | InlineAsmOperand::SymStatic { def_id: _ } => {}
+                        | InlineAsmOperand::SymStatic { def_id: _ }
+                        | InlineAsmOperand::Label { target_index: _ } => {}
                     }
                 }
             }