Rollup merge of #131523 - nbdd0121:asm, r=compiler-errors

Fix asm goto with outputs and move it to a separate feature gate

Tracking issue: #119364

This PR addresses 3 aspects of asm goto with outputs:
* Codegen is fixed. My initial implementation has an oversight which cause the output to be only stored in fallthrough path, but not in label blocks.
* Outputs can now be used with `options(noreturn)` if a label block is given.
* All of this is moved to a new feature gate, because we likely want to stabilise `asm_goto` before asm goto with outputs.

`@rustbot` labels: +A-inline-assembly +F-asm

compiler/rustc_ast_lowering/messages.ftl

@@ -181,6 +181,8 @@ ast_lowering_underscore_expr_lhs_assign =
     .label = `_` not allowed here
 
 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

compiler/rustc_ast_lowering/src/asm.rs

@@ -239,15 +239,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         }
                     }
                     InlineAsmOperand::Label { block } => {
-                        if !self.tcx.features().asm_goto() {
-                            feature_err(
-                                sess,
-                                sym::asm_goto,
-                                *op_sp,
-                                fluent::ast_lowering_unstable_inline_assembly_label_operands,
-                            )
-                            .emit();
-                        }
                         hir::InlineAsmOperand::Label { block: self.lower_block(block, false) }
                     }
                 };
@@ -466,6 +457,41 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             }
         }
 
+        // Feature gate checking for asm goto.
+        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.
+            let output_operand_used = operands.iter().any(|(op, _)| {
+                matches!(
+                    op,
+                    hir::InlineAsmOperand::Out { expr: Some(_), .. }
+                        | hir::InlineAsmOperand::InOut { .. }
+                        | hir::InlineAsmOperand::SplitInOut { out_expr: Some(_), .. }
+                )
+            });
+            if output_operand_used && !self.tcx.features().asm_goto_with_outputs() {
+                feature_err(
+                    sess,
+                    sym::asm_goto_with_outputs,
+                    *op_sp,
+                    fluent::ast_lowering_unstable_inline_assembly_label_operand_with_outputs,
+                )
+                .emit();
+            }
+        }
+
         let operands = self.arena.alloc_from_iter(operands);
         let template = self.arena.alloc_from_iter(asm.template.iter().cloned());
         let template_strs = self.arena.alloc_from_iter(

compiler/rustc_builtin_macros/src/asm.rs

@@ -300,7 +300,10 @@ pub fn parse_asm_args<'a>(
     if args.options.contains(ast::InlineAsmOptions::PURE) && !have_real_output {
         dcx.emit_err(errors::AsmPureNoOutput { spans: args.options_spans.clone() });
     }
-    if args.options.contains(ast::InlineAsmOptions::NORETURN) && !outputs_sp.is_empty() {
+    if args.options.contains(ast::InlineAsmOptions::NORETURN)
+        && !outputs_sp.is_empty()
+        && labels_sp.is_empty()
+    {
         let err = dcx.create_err(errors::AsmNoReturn { outputs_sp });
         // Bail out now since this is likely to confuse MIR
         return Err(err);

compiler/rustc_codegen_llvm/src/asm.rs

@@ -342,24 +342,32 @@ impl<'ll, 'tcx> AsmBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
         }
         attributes::apply_to_callsite(result, llvm::AttributePlace::Function, &{ attrs });
 
-        // Switch to the 'normal' basic block if we did an `invoke` instead of a `call`
-        if let Some(dest) = dest {
-            self.switch_to_block(dest);
-        }
+        // Write results to outputs. We need to do this for all possible control flow.
+        //
+        // Note that `dest` maybe populated with unreachable_block when asm goto with outputs
+        // is used (because we need to codegen callbr which always needs a destination), so
+        // here we use the NORETURN option to determine if `dest` should be used.
+        for block in (if options.contains(InlineAsmOptions::NORETURN) { None } else { Some(dest) })
+            .into_iter()
+            .chain(labels.iter().copied().map(Some))
+        {
+            if let Some(block) = block {
+                self.switch_to_block(block);
+            }
 
-        // Write results to outputs
-        for (idx, op) in operands.iter().enumerate() {
-            if let InlineAsmOperandRef::Out { reg, place: Some(place), .. }
-            | InlineAsmOperandRef::InOut { reg, out_place: Some(place), .. } = *op
-            {
-                let value = if output_types.len() == 1 {
-                    result
-                } else {
-                    self.extract_value(result, op_idx[&idx] as u64)
-                };
-                let value =
-                    llvm_fixup_output(self, value, reg.reg_class(), &place.layout, instance);
-                OperandValue::Immediate(value).store(self, place);
+            for (idx, op) in operands.iter().enumerate() {
+                if let InlineAsmOperandRef::Out { reg, place: Some(place), .. }
+                | InlineAsmOperandRef::InOut { reg, out_place: Some(place), .. } = *op
+                {
+                    let value = if output_types.len() == 1 {
+                        result
+                    } else {
+                        self.extract_value(result, op_idx[&idx] as u64)
+                    };
+                    let value =
+                        llvm_fixup_output(self, value, reg.reg_class(), &place.layout, instance);
+                    OperandValue::Immediate(value).store(self, place);
+                }
             }
         }
     }

compiler/rustc_feature/src/unstable.rs

@@ -378,6 +378,8 @@ declare_features! (
     (unstable, asm_experimental_arch, "1.58.0", Some(93335)),
     /// 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, "CURRENT_RUSTC_VERSION", Some(119364)),
     /// Allows the `may_unwind` option in inline assembly.
     (unstable, asm_unwind, "1.58.0", Some(93334)),
     /// Allows users to enforce equality of associated constants `TraitImpl<AssocConst=3>`.

compiler/rustc_span/src/symbol.rs

@@ -417,6 +417,7 @@ symbols! {
         asm_const,
         asm_experimental_arch,
         asm_goto,
+        asm_goto_with_outputs,
         asm_sym,
         asm_unwind,
         assert,