Auto merge of rust-lang#96800 - nbdd0121:const, r=nagisa

Permit `asm_const` and `asm_sym` to reference generic params

Related rust-lang#96557

These constructs will be allowed:
```rust
fn foofoo<const N: usize>() {}

unsafe fn foo<const N: usize>() {
    asm!("/* {0} */", const N);
    asm!("/* {0} */", const N + 1);
    asm!("/* {0} */", sym foofoo::<N>);
}

fn barbar<T>() {}

unsafe fn bar<T>() {
    asm!("/* {0} */", const std::mem::size_of::<T>());
    asm!("/* {0} */", const std::mem::size_of::<(T, T)>());
    asm!("/* {0} */", sym barbar::<T>);
    asm!("/* {0} */", sym barbar::<(T, T)>);
}
```

`@Amanieu,` I didn't switch inline asms to use `DefKind::InlineAsm`, as I see little value doing that; given that no type inference is needed, it will only make typecking slower and more complex but will have no real gains. I did switch them to follow the same code path as inline asm during symbol resolution, though.
The `error: unconstrained generic constant` you mentioned in rust-lang#76001 is due to the fact that `to_const` will actually add a wfness obligation to the constant, which we don't need for `asm_const`, so I have that removed.

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

compiler/rustc_ast/src/visit.rs

@@ -326,7 +326,7 @@ pub fn walk_item<'a, V: Visitor<'a>>(visitor: &mut V, item: &'a Item) {
         ItemKind::ForeignMod(ref foreign_module) => {
             walk_list!(visitor, visit_foreign_item, &foreign_module.items);
         }
-        ItemKind::GlobalAsm(ref asm) => walk_inline_asm(visitor, asm),
+        ItemKind::GlobalAsm(ref asm) => visitor.visit_inline_asm(asm),
         ItemKind::TyAlias(box TyAlias { ref generics, ref bounds, ref ty, .. }) => {
             visitor.visit_generics(generics);
             walk_list!(visitor, visit_param_bound, bounds, BoundKind::Bound);
@@ -897,7 +897,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
         }
         ExprKind::MacCall(ref mac) => visitor.visit_mac_call(mac),
         ExprKind::Paren(ref subexpression) => visitor.visit_expr(subexpression),
-        ExprKind::InlineAsm(ref asm) => walk_inline_asm(visitor, asm),
+        ExprKind::InlineAsm(ref asm) => visitor.visit_inline_asm(asm),
         ExprKind::Yield(ref optional_expression) => {
             walk_list!(visitor, visit_expr, optional_expression);
         }

compiler/rustc_resolve/src/ident.rs

@@ -1171,6 +1171,7 @@ impl<'a> Resolver<'a> {
                         | AssocItemRibKind
                         | ModuleRibKind(..)
                         | MacroDefinition(..)
+                        | InlineAsmSymRibKind
                         | ForwardGenericParamBanRibKind => {
                             // Nothing to do. Continue.
                             continue;
@@ -1216,22 +1217,6 @@ impl<'a> Resolver<'a> {
                             }
                             return Res::Err;
                         }
-                        InlineAsmSymRibKind => {
-                            let features = self.session.features_untracked();
-                            if !features.generic_const_exprs {
-                                if let Some(span) = finalize {
-                                    self.report_error(
-                                        span,
-                                        ResolutionError::ParamInNonTrivialAnonConst {
-                                            name: rib_ident.name,
-                                            is_type: true,
-                                        },
-                                    );
-                                }
-                                return Res::Err;
-                            }
-                            continue;
-                        }
                     };
 
                     if let Some(span) = finalize {
@@ -1262,6 +1247,7 @@ impl<'a> Resolver<'a> {
                         | AssocItemRibKind
                         | ModuleRibKind(..)
                         | MacroDefinition(..)
+                        | InlineAsmSymRibKind
                         | ForwardGenericParamBanRibKind => continue,
 
                         ConstantItemRibKind(trivial, _) => {
@@ -1296,22 +1282,6 @@ impl<'a> Resolver<'a> {
                             }
                             return Res::Err;
                         }
-                        InlineAsmSymRibKind => {
-                            let features = self.session.features_untracked();
-                            if !features.generic_const_exprs {
-                                if let Some(span) = finalize {
-                                    self.report_error(
-                                        span,
-                                        ResolutionError::ParamInNonTrivialAnonConst {
-                                            name: rib_ident.name,
-                                            is_type: false,
-                                        },
-                                    );
-                                }
-                                return Res::Err;
-                            }
-                            continue;
-                        }
                     };
 
                     // This was an attempt to use a const parameter outside its scope.

compiler/rustc_resolve/src/late.rs

@@ -918,6 +918,29 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
         self.diagnostic_metadata.current_where_predicate = previous_value;
     }
 
+    fn visit_inline_asm(&mut self, asm: &'ast InlineAsm) {
+        for (op, _) in &asm.operands {
+            match op {
+                InlineAsmOperand::In { expr, .. }
+                | InlineAsmOperand::Out { expr: Some(expr), .. }
+                | InlineAsmOperand::InOut { expr, .. } => self.visit_expr(expr),
+                InlineAsmOperand::Out { expr: None, .. } => {}
+                InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
+                    self.visit_expr(in_expr);
+                    if let Some(out_expr) = out_expr {
+                        self.visit_expr(out_expr);
+                    }
+                }
+                InlineAsmOperand::Const { anon_const, .. } => {
+                    // Although this is `DefKind::AnonConst`, it is allowed to reference outer
+                    // generic parameters like an inline const.
+                    self.resolve_inline_const(anon_const);
+                }
+                InlineAsmOperand::Sym { sym } => self.visit_inline_asm_sym(sym),
+            }
+        }
+    }
+
     fn visit_inline_asm_sym(&mut self, sym: &'ast InlineAsmSym) {
         // This is similar to the code for AnonConst.
         self.with_rib(ValueNS, InlineAsmSymRibKind, |this| {

compiler/rustc_typeck/src/check/expr.rs

@@ -2641,10 +2641,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         self.check_expr_asm_operand(out_expr, false);
                     }
                 }
-                hir::InlineAsmOperand::Const { anon_const }
-                | hir::InlineAsmOperand::SymFn { anon_const } => {
-                    self.to_const(anon_const);
-                }
+                // `AnonConst`s have their own body and is type-checked separately.
+                // As they don't flow into the type system we don't need them to
+                // be well-formed.
+                hir::InlineAsmOperand::Const { .. } | hir::InlineAsmOperand::SymFn { .. } => {}
                 hir::InlineAsmOperand::SymStatic { .. } => {}
             }
         }

compiler/rustc_typeck/src/collect.rs

@@ -1556,6 +1556,18 @@ fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
                     Node::Expr(&Expr { kind: ExprKind::ConstBlock(_), .. }) => {
                         Some(tcx.typeck_root_def_id(def_id))
                     }
+                    // Exclude `GlobalAsm` here which cannot have generics.
+                    Node::Expr(&Expr { kind: ExprKind::InlineAsm(asm), .. })
+                        if asm.operands.iter().any(|(op, _op_sp)| match op {
+                            hir::InlineAsmOperand::Const { anon_const }
+                            | hir::InlineAsmOperand::SymFn { anon_const } => {
+                                anon_const.hir_id == hir_id
+                            }
+                            _ => false,
+                        }) =>
+                    {
+                        Some(parent_def_id.to_def_id())
+                    }
                     _ => None,
                 }
             }

src/test/ui/asm/generic-const.rs

@@ -0,0 +1,30 @@
+// needs-asm-support
+// build-pass
+
+#![feature(asm_const, asm_sym)]
+
+use std::arch::asm;
+
+fn foofoo<const N: usize>() {}
+
+unsafe fn foo<const N: usize>() {
+    asm!("/* {0} */", const N);
+    asm!("/* {0} */", const N + 1);
+    asm!("/* {0} */", sym foofoo::<N>);
+}
+
+fn barbar<T>() {}
+
+unsafe fn bar<T>() {
+    asm!("/* {0} */", const std::mem::size_of::<T>());
+    asm!("/* {0} */", const std::mem::size_of::<(T, T)>());
+    asm!("/* {0} */", sym barbar::<T>);
+    asm!("/* {0} */", sym barbar::<(T, T)>);
+}
+
+fn main() {
+    unsafe {
+        foo::<0>();
+        bar::<usize>();
+    }
+}

src/test/ui/asm/type-check-1.rs

@@ -63,7 +63,6 @@ fn main() {
 
 unsafe fn generic<T>() {
     asm!("{}", sym generic::<T>);
-    //~^ generic parameters may not be used in const operations
 }
 
 // Const operands must be integers and must be constants.

src/test/ui/asm/type-check-1.stderr

@@ -33,15 +33,6 @@ LL |         asm!("{}", sym x);
    |
    = help: `sym` operands must refer to either a function or a static
 
-error: generic parameters may not be used in const operations
-  --> $DIR/type-check-1.rs:65:30
-   |
-LL |     asm!("{}", sym generic::<T>);
-   |                              ^ cannot perform const operation using `T`
-   |
-   = note: type parameters may not be used in const expressions
-   = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
-
 error[E0308]: mismatched types
   --> $DIR/type-check-1.rs:55:26
    |
@@ -109,21 +100,21 @@ LL |         asm!("{}", inout(reg) v[..]);
    = note: all inline asm arguments must have a statically known size
 
 error[E0308]: mismatched types
-  --> $DIR/type-check-1.rs:74:25
+  --> $DIR/type-check-1.rs:73:25
    |
 LL | global_asm!("{}", const 0f32);
    |                         ^^^^ expected integer, found `f32`
 
 error[E0308]: mismatched types
-  --> $DIR/type-check-1.rs:76:25
+  --> $DIR/type-check-1.rs:75:25
    |
 LL | global_asm!("{}", const 0 as *mut u8);
    |                         ^^^^^^^^^^^^ expected integer, found *-ptr
    |
    = note:     expected type `{integer}`
            found raw pointer `*mut u8`
 
-error: aborting due to 15 previous errors
+error: aborting due to 14 previous errors
 
 Some errors have detailed explanations: E0277, E0308, E0435.
 For more information about an error, try `rustc --explain E0277`.

src/test/ui/feature-gates/feature-gate-asm_const.rs

@@ -2,8 +2,14 @@
 
 use std::arch::asm;
 
+unsafe fn foo<const N: usize>() {
+    asm!("mov eax, {}", const N + 1);
+    //~^ ERROR const operands for inline assembly are unstable
+}
+
 fn main() {
     unsafe {
+        foo::<0>();
         asm!("mov eax, {}", const 123);
         //~^ ERROR const operands for inline assembly are unstable
     }

src/test/ui/feature-gates/feature-gate-asm_const.stderr

@@ -1,12 +1,21 @@
 error[E0658]: const operands for inline assembly are unstable
-  --> $DIR/feature-gate-asm_const.rs:7:29
+  --> $DIR/feature-gate-asm_const.rs:6:25
+   |
+LL |     asm!("mov eax, {}", const N + 1);
+   |                         ^^^^^^^^^^^
+   |
+   = note: see issue #93332 <https://github.com/rust-lang/rust/issues/93332> for more information
+   = help: add `#![feature(asm_const)]` to the crate attributes to enable
+
+error[E0658]: const operands for inline assembly are unstable
+  --> $DIR/feature-gate-asm_const.rs:13:29
    |
 LL |         asm!("mov eax, {}", const 123);
    |                             ^^^^^^^^^
    |
    = note: see issue #93332 <https://github.com/rust-lang/rust/issues/93332> for more information
    = help: add `#![feature(asm_const)]` to the crate attributes to enable
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0658`.

src/test/ui/feature-gates/feature-gate-asm_sym.rs

@@ -2,9 +2,18 @@
 
 use std::arch::asm;
 
+fn bar<const N: usize>() {}
+
+fn foo<const N: usize>() {
+    unsafe {
+        asm!("mov eax, {}", sym bar::<N>);
+        //~^ ERROR sym operands for inline assembly are unstable
+    }
+}
+
 fn main() {
     unsafe {
-        asm!("mov eax, {}", sym main);
+        asm!("mov eax, {}", sym foo::<0>);
         //~^ ERROR sym operands for inline assembly are unstable
     }
 }

src/test/ui/feature-gates/feature-gate-asm_sym.stderr

@@ -1,12 +1,21 @@
 error[E0658]: sym operands for inline assembly are unstable
-  --> $DIR/feature-gate-asm_sym.rs:7:29
+  --> $DIR/feature-gate-asm_sym.rs:9:29
    |
-LL |         asm!("mov eax, {}", sym main);
-   |                             ^^^^^^^^
+LL |         asm!("mov eax, {}", sym bar::<N>);
+   |                             ^^^^^^^^^^^^
    |
    = note: see issue #93333 <https://github.com/rust-lang/rust/issues/93333> for more information
    = help: add `#![feature(asm_sym)]` to the crate attributes to enable
 
-error: aborting due to previous error
+error[E0658]: sym operands for inline assembly are unstable
+  --> $DIR/feature-gate-asm_sym.rs:16:29
+   |
+LL |         asm!("mov eax, {}", sym foo::<0>);
+   |                             ^^^^^^^^^^^^
+   |
+   = note: see issue #93333 <https://github.com/rust-lang/rust/issues/93333> for more information
+   = help: add `#![feature(asm_sym)]` to the crate attributes to enable
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0658`.