Auto merge of #94468 - Amanieu:global_asm_sym, r=nagisa

Implement sym operands for global_asm!

Tracking issue: #93333

This PR is pretty much a complete rewrite of `sym` operand support for inline assembly so that the same implementation can be shared by `asm!` and `global_asm!`. The main changes are:
- At the AST level, `sym` is represented as a special `InlineAsmSym` AST node containing a path instead of an `Expr`.
- At the HIR level, `sym` is split into `SymStatic` and `SymFn` depending on whether the path resolves to a static during AST lowering (defaults to `SynFn` if `get_early_res` fails).
  - `SymFn` is just an `AnonConst`. It runs through typeck and we just collect the resulting type at the end. An error is emitted if the type is not a `FnDef`.
  - `SymStatic` directly holds a path and the `DefId` of the `static` that it is pointing to.
- The representation at the MIR level is mostly unchanged. There is a minor change to THIR where `SymFn` is a constant instead of an expression.
- At the codegen level we need to apply the target's symbol mangling to the result of `tcx.symbol_name()` depending on the target. This is done by calling the LLVM name mangler, which handles all of the details.
  - On Mach-O, all symbols have a leading underscore.
  - On x86 Windows, different mangling is used for cdecl, stdcall, fastcall and vectorcall.
  - No mangling is needed on other platforms.

r? `@nagisa`
cc `@eddyb`

3 files changed, 30 insertions, 6 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mono_item.rs b/compiler/rustc_codegen_ssa/src/mono_item.rs
index 5414c619dcb..5006a2157fc 100644
--- a/compiler/rustc_codegen_ssa/src/mono_item.rs
+++ b/compiler/rustc_codegen_ssa/src/mono_item.rs
@@ -4,7 +4,9 @@ use crate::traits::*;
 use rustc_hir as hir;
 use rustc_middle::mir::mono::MonoItem;
 use rustc_middle::mir::mono::{Linkage, Visibility};
+use rustc_middle::ty;
 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
+use rustc_middle::ty::Instance;
 
 pub trait MonoItemExt<'a, 'tcx> {
     fn define<Bx: BuilderMethods<'a, 'tcx>>(&self, cx: &'a Bx::CodegenCx);
@@ -56,7 +58,27 @@ impl<'a, 'tcx: 'a> MonoItemExt<'a, 'tcx> for MonoItem<'tcx> {
                                 );
                                 GlobalAsmOperandRef::Const { string }
                             }
-                            _ => span_bug!(*op_sp, "invalid operand type for global_asm!"),
+                            hir::InlineAsmOperand::SymFn { ref anon_const } => {
+                                let ty = cx
+                                    .tcx()
+                                    .typeck_body(anon_const.body)
+                                    .node_type(anon_const.hir_id);
+                                let instance = match ty.kind() {
+                                    &ty::FnDef(def_id, substs) => Instance::new(def_id, substs),
+                                    _ => span_bug!(*op_sp, "asm sym is not a function"),
+                                };
+
+                                GlobalAsmOperandRef::SymFn { instance }
+                            }
+                            hir::InlineAsmOperand::SymStatic { path: _, def_id } => {
+                                GlobalAsmOperandRef::SymStatic { def_id }
+                            }
+                            hir::InlineAsmOperand::In { .. }
+                            | hir::InlineAsmOperand::Out { .. }
+                            | hir::InlineAsmOperand::InOut { .. }
+                            | hir::InlineAsmOperand::SplitInOut { .. } => {
+                                span_bug!(*op_sp, "invalid operand type for global_asm!")
+                            }
                         })
                         .collect();
 
diff --git a/compiler/rustc_codegen_ssa/src/traits/asm.rs b/compiler/rustc_codegen_ssa/src/traits/asm.rs
index 11111a79744..c2ae74b18d8 100644
--- a/compiler/rustc_codegen_ssa/src/traits/asm.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/asm.rs
@@ -36,8 +36,10 @@ pub enum InlineAsmOperandRef<'tcx, B: BackendTypes + ?Sized> {
 }
 
 #[derive(Debug)]
-pub enum GlobalAsmOperandRef {
+pub enum GlobalAsmOperandRef<'tcx> {
     Const { string: String },
+    SymFn { instance: Instance<'tcx> },
+    SymStatic { def_id: DefId },
 }
 
 pub trait AsmBuilderMethods<'tcx>: BackendTypes {
@@ -53,11 +55,11 @@ pub trait AsmBuilderMethods<'tcx>: BackendTypes {
     );
 }
 
-pub trait AsmMethods {
+pub trait AsmMethods<'tcx> {
     fn codegen_global_asm(
         &self,
         template: &[InlineAsmTemplatePiece],
-        operands: &[GlobalAsmOperandRef],
+        operands: &[GlobalAsmOperandRef<'tcx>],
         options: InlineAsmOptions,
         line_spans: &[Span],
     );
diff --git a/compiler/rustc_codegen_ssa/src/traits/mod.rs b/compiler/rustc_codegen_ssa/src/traits/mod.rs
index c529fbbf518..396768e0a42 100644
--- a/compiler/rustc_codegen_ssa/src/traits/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/mod.rs
@@ -60,7 +60,7 @@ pub trait CodegenMethods<'tcx>:
     + StaticMethods
     + CoverageInfoMethods<'tcx>
     + DebugInfoMethods<'tcx>
-    + AsmMethods
+    + AsmMethods<'tcx>
     + PreDefineMethods<'tcx>
     + HasParamEnv<'tcx>
     + HasTyCtxt<'tcx>
@@ -76,7 +76,7 @@ impl<'tcx, T> CodegenMethods<'tcx> for T where
         + StaticMethods
         + CoverageInfoMethods<'tcx>
         + DebugInfoMethods<'tcx>
-        + AsmMethods
+        + AsmMethods<'tcx>
         + PreDefineMethods<'tcx>
         + HasParamEnv<'tcx>
         + HasTyCtxt<'tcx>