Auto merge of rust-lang#119365 - nbdd0121:asm-goto, r=Amanieu

Add asm goto support to `asm!`

Tracking issue: rust-lang#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`

Author: bors

compiler/rustc_ast/src/ast.rs

@@ -2294,6 +2294,9 @@ pub enum InlineAsmOperand {
     Sym {
         sym: InlineAsmSym,
     },
+    Label {
+        block: P<Block>,
+    },
 }
 
 impl InlineAsmOperand {
@@ -2303,7 +2306,7 @@ impl InlineAsmOperand {
             | Self::Out { reg, .. }
             | Self::InOut { reg, .. }
             | Self::SplitInOut { reg, .. } => Some(reg),
-            Self::Const { .. } | Self::Sym { .. } => None,
+            Self::Const { .. } | Self::Sym { .. } | Self::Label { .. } => None,
         }
     }
 }

compiler/rustc_ast/src/mut_visit.rs

@@ -1330,6 +1330,7 @@ pub fn noop_visit_inline_asm<T: MutVisitor>(asm: &mut InlineAsm, vis: &mut T) {
             }
             InlineAsmOperand::Const { anon_const } => vis.visit_anon_const(anon_const),
             InlineAsmOperand::Sym { sym } => vis.visit_inline_asm_sym(sym),
+            InlineAsmOperand::Label { block } => vis.visit_block(block),
         }
     }
 }

compiler/rustc_ast/src/visit.rs

@@ -885,6 +885,7 @@ pub fn walk_inline_asm<'a, V: Visitor<'a>>(visitor: &mut V, asm: &'a InlineAsm)
                 try_visit!(visitor.visit_anon_const(anon_const))
             }
             InlineAsmOperand::Sym { sym } => try_visit!(visitor.visit_inline_asm_sym(sym)),
+            InlineAsmOperand::Label { block } => try_visit!(visitor.visit_block(block)),
         }
     }
     V::Result::output()

compiler/rustc_ast_lowering/messages.ftl

@@ -88,6 +88,9 @@ ast_lowering_invalid_abi_suggestion = did you mean
 ast_lowering_invalid_asm_template_modifier_const =
     asm template modifiers are not allowed for `const` arguments
 
+ast_lowering_invalid_asm_template_modifier_label =
+    asm template modifiers are not allowed for `label` arguments
+
 ast_lowering_invalid_asm_template_modifier_reg_class =
     invalid asm template modifier for this register class
 

compiler/rustc_ast_lowering/src/asm.rs

@@ -3,9 +3,9 @@ use crate::{ImplTraitContext, ImplTraitPosition, ParamMode, ResolverAstLoweringE
 use super::errors::{
     AbiSpecifiedMultipleTimes, AttSyntaxOnlyX86, ClobberAbiNotSupported,
     InlineAsmUnsupportedTarget, InvalidAbiClobberAbi, InvalidAsmTemplateModifierConst,
-    InvalidAsmTemplateModifierRegClass, InvalidAsmTemplateModifierRegClassSub,
-    InvalidAsmTemplateModifierSym, InvalidRegister, InvalidRegisterClass, RegisterClassOnlyClobber,
-    RegisterConflict,
+    InvalidAsmTemplateModifierLabel, InvalidAsmTemplateModifierRegClass,
+    InvalidAsmTemplateModifierRegClassSub, InvalidAsmTemplateModifierSym, InvalidRegister,
+    InvalidRegisterClass, RegisterClassOnlyClobber, RegisterConflict,
 };
 use super::LoweringContext;
 
@@ -236,6 +236,18 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             }
                         }
                     }
+                    InlineAsmOperand::Label { block } => {
+                        if !self.tcx.features().asm_goto {
+                            feature_err(
+                                sess,
+                                sym::asm_goto,
+                                *op_sp,
+                                "label operands for inline assembly are unstable",
+                            )
+                            .emit();
+                        }
+                        hir::InlineAsmOperand::Label { block: self.lower_block(block, false) }
+                    }
                 };
                 (op, self.lower_span(*op_sp))
             })
@@ -295,6 +307,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             op_span: op_sp,
                         });
                     }
+                    hir::InlineAsmOperand::Label { .. } => {
+                        self.dcx().emit_err(InvalidAsmTemplateModifierLabel {
+                            placeholder_span,
+                            op_span: op_sp,
+                        });
+                    }
                 }
             }
         }
@@ -334,7 +352,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                         hir::InlineAsmOperand::Const { .. }
                         | hir::InlineAsmOperand::SymFn { .. }
-                        | hir::InlineAsmOperand::SymStatic { .. } => {
+                        | hir::InlineAsmOperand::SymStatic { .. }
+                        | hir::InlineAsmOperand::Label { .. } => {
                             unreachable!("{op:?} is not a register operand");
                         }
                     };

compiler/rustc_ast_lowering/src/errors.rs

@@ -262,6 +262,16 @@ pub struct InvalidAsmTemplateModifierSym {
     pub op_span: Span,
 }
 
+#[derive(Diagnostic, Clone, Copy)]
+#[diag(ast_lowering_invalid_asm_template_modifier_label)]
+pub struct InvalidAsmTemplateModifierLabel {
+    #[primary_span]
+    #[label(ast_lowering_template_modifier)]
+    pub placeholder_span: Span,
+    #[label(ast_lowering_argument)]
+    pub op_span: Span,
+}
+
 #[derive(Diagnostic, Clone, Copy)]
 #[diag(ast_lowering_register_class_only_clobber)]
 pub struct RegisterClassOnlyClobber {

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1331,6 +1331,10 @@ impl<'a> State<'a> {
                             s.print_path(&sym.path, true, 0);
                         }
                     }
+                    InlineAsmOperand::Label { block } => {
+                        s.head("label");
+                        s.print_block(block);
+                    }
                 }
             }
             AsmArg::ClobberAbi(abi) => {

compiler/rustc_borrowck/src/lib.rs

@@ -723,7 +723,7 @@ impl<'cx, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx, R> for MirBorro
                 operands,
                 options: _,
                 line_spans: _,
-                destination: _,
+                targets: _,
                 unwind: _,
             } => {
                 for op in operands {
@@ -749,7 +749,8 @@ impl<'cx, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx, R> for MirBorro
                         }
                         InlineAsmOperand::Const { value: _ }
                         | InlineAsmOperand::SymFn { value: _ }
-                        | InlineAsmOperand::SymStatic { def_id: _ } => {}
+                        | InlineAsmOperand::SymStatic { def_id: _ }
+                        | InlineAsmOperand::Label { target_index: _ } => {}
                     }
                 }
             }

compiler/rustc_borrowck/src/polonius/loan_invalidations.rs

@@ -161,7 +161,7 @@ impl<'cx, 'tcx> Visitor<'tcx> for LoanInvalidationsGenerator<'cx, 'tcx> {
                 operands,
                 options: _,
                 line_spans: _,
-                destination: _,
+                targets: _,
                 unwind: _,
             } => {
                 for op in operands {
@@ -182,7 +182,8 @@ impl<'cx, 'tcx> Visitor<'tcx> for LoanInvalidationsGenerator<'cx, 'tcx> {
                         }
                         InlineAsmOperand::Const { value: _ }
                         | InlineAsmOperand::SymFn { value: _ }
-                        | InlineAsmOperand::SymStatic { def_id: _ } => {}
+                        | InlineAsmOperand::SymStatic { def_id: _ }
+                        | InlineAsmOperand::Label { target_index: _ } => {}
                     }
                 }
             }

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1771,8 +1771,8 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
                 self.assert_iscleanup_unwind(body, block_data, unwind, is_cleanup);
             }
-            TerminatorKind::InlineAsm { destination, unwind, .. } => {
-                if let Some(target) = destination {
+            TerminatorKind::InlineAsm { ref targets, unwind, .. } => {
+                for &target in targets {
                     self.assert_iscleanup(body, block_data, target, is_cleanup);
                 }
                 self.assert_iscleanup_unwind(body, block_data, unwind, is_cleanup);