Use gimli to get the values of DWARF constants needed by codegen

The `gimli` crate is already a dependency of `thorin-dwp`, which is already a
dependency of `rustc_codegen_ssa`.

Author: Zalathar

Diff for: Cargo.lock

@@ -3499,6 +3499,7 @@ name = "rustc_codegen_llvm"
 version = "0.0.0"
 dependencies = [
  "bitflags",
+ "gimli 0.30.0",
  "itertools",
  "libc",
  "measureme",

Diff for: compiler/rustc_codegen_llvm/Cargo.toml

@@ -9,6 +9,7 @@ test = false
 [dependencies]
 # tidy-alphabetical-start
 bitflags = "2.4.1"
+gimli = "0.30"
 itertools = "0.12"
 libc = "0.2"
 measureme = "11"

Diff for: compiler/rustc_codegen_llvm/src/debuginfo/dwarf_const.rs

@@ -0,0 +1,29 @@
+//! Definitions of various DWARF-related constants.
+
+use libc::c_uint;
+
+/// Helper macro to let us redeclare gimli's constants as our own constants
+/// with a different type, with less risk of copy-paste errors.
+macro_rules! declare_constant {
+    (
+        $name:ident : $type:ty
+    ) => {
+        #[allow(non_upper_case_globals)]
+        pub(crate) const $name: $type = ::gimli::constants::$name.0 as $type;
+
+        // Assert that as-cast probably hasn't changed the value.
+        const _: () = assert!($name as i128 == ::gimli::constants::$name.0 as i128);
+    };
+}
+
+declare_constant!(DW_TAG_const_type: c_uint);
+
+// DWARF languages.
+declare_constant!(DW_LANG_Rust: c_uint);
+
+// DWARF attribute type encodings.
+declare_constant!(DW_ATE_boolean: c_uint);
+declare_constant!(DW_ATE_float: c_uint);
+declare_constant!(DW_ATE_signed: c_uint);
+declare_constant!(DW_ATE_unsigned: c_uint);
+declare_constant!(DW_ATE_UTF: c_uint);

Diff for: compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -22,6 +22,7 @@ use rustc_target::spec::DebuginfoKind;
 use smallvec::smallvec;
 use tracing::{debug, instrument};
 
+pub(crate) use self::type_map::TypeMap;
 use self::type_map::{DINodeCreationResult, Stub, UniqueTypeId};
 use super::CodegenUnitDebugContext;
 use super::namespace::mangled_name_of_instance;
@@ -30,6 +31,7 @@ use super::utils::{
     DIB, create_DIArray, debug_context, get_namespace_for_item, is_node_local_to_unit,
 };
 use crate::common::{AsCCharPtr, CodegenCx};
+use crate::debuginfo::dwarf_const;
 use crate::debuginfo::metadata::type_map::build_type_with_children;
 use crate::debuginfo::utils::{WidePtrKind, wide_pointer_kind};
 use crate::llvm::debuginfo::{
@@ -59,23 +61,6 @@ impl fmt::Debug for llvm::Metadata {
     }
 }
 
-// From DWARF 5.
-// See http://www.dwarfstd.org/ShowIssue.php?issue=140129.1.
-const DW_LANG_RUST: c_uint = 0x1c;
-#[allow(non_upper_case_globals)]
-const DW_ATE_boolean: c_uint = 0x02;
-#[allow(non_upper_case_globals)]
-const DW_ATE_float: c_uint = 0x04;
-#[allow(non_upper_case_globals)]
-const DW_ATE_signed: c_uint = 0x05;
-#[allow(non_upper_case_globals)]
-const DW_ATE_unsigned: c_uint = 0x07;
-#[allow(non_upper_case_globals)]
-const DW_ATE_UTF: c_uint = 0x10;
-
-#[allow(non_upper_case_globals)]
-const DW_TAG_const_type: c_uint = 0x26;
-
 pub(super) const UNKNOWN_LINE_NUMBER: c_uint = 0;
 pub(super) const UNKNOWN_COLUMN_NUMBER: c_uint = 0;
 
@@ -90,8 +75,6 @@ type SmallVec<T> = smallvec::SmallVec<[T; 16]>;
 mod enums;
 mod type_map;
 
-pub(crate) use type_map::TypeMap;
-
 /// Returns from the enclosing function if the type debuginfo node with the given
 /// unique ID can be found in the type map.
 macro_rules! return_if_di_node_created_in_meantime {
@@ -522,7 +505,7 @@ fn recursion_marker_type_di_node<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) -> &'ll D
                 name.as_c_char_ptr(),
                 name.len(),
                 cx.tcx.data_layout.pointer_size.bits(),
-                DW_ATE_unsigned,
+                dwarf_const::DW_ATE_unsigned,
             )
         }
     })
@@ -781,6 +764,8 @@ fn build_basic_type_di_node<'ll, 'tcx>(
     // .natvis visualizers (and perhaps other existing native debuggers?)
     let cpp_like_debuginfo = cpp_like_debuginfo(cx.tcx);
 
+    use dwarf_const::{DW_ATE_UTF, DW_ATE_boolean, DW_ATE_float, DW_ATE_signed, DW_ATE_unsigned};
+
     let (name, encoding) = match t.kind() {
         ty::Never => ("!", DW_ATE_unsigned),
         ty::Tuple(elements) if elements.is_empty() => {
@@ -961,7 +946,7 @@ pub(crate) fn build_compile_unit_di_node<'ll, 'tcx>(
 
         let unit_metadata = llvm::LLVMRustDIBuilderCreateCompileUnit(
             debug_context.builder,
-            DW_LANG_RUST,
+            dwarf_const::DW_LANG_Rust,
             compile_unit_file,
             producer.as_c_char_ptr(),
             producer.len(),

Diff for: compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/cpp_like.rs

@@ -12,12 +12,13 @@ use rustc_middle::ty::{self, AdtDef, CoroutineArgs, CoroutineArgsExt, Ty};
 use smallvec::smallvec;
 
 use crate::common::{AsCCharPtr, CodegenCx};
+use crate::debuginfo::dwarf_const::DW_TAG_const_type;
 use crate::debuginfo::metadata::enums::DiscrResult;
 use crate::debuginfo::metadata::type_map::{self, Stub, UniqueTypeId};
 use crate::debuginfo::metadata::{
-    DINodeCreationResult, DW_TAG_const_type, NO_GENERICS, NO_SCOPE_METADATA, SmallVec,
-    UNKNOWN_LINE_NUMBER, build_field_di_node, file_metadata, file_metadata_from_def_id,
-    size_and_align_of, type_di_node, unknown_file_metadata, visibility_di_flags,
+    DINodeCreationResult, NO_GENERICS, NO_SCOPE_METADATA, SmallVec, UNKNOWN_LINE_NUMBER,
+    build_field_di_node, file_metadata, file_metadata_from_def_id, size_and_align_of, type_di_node,
+    unknown_file_metadata, visibility_di_flags,
 };
 use crate::debuginfo::utils::DIB;
 use crate::llvm::debuginfo::{DIFile, DIFlags, DIType};

Diff for: compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -39,6 +39,7 @@ use crate::llvm::debuginfo::{
 use crate::value::Value;
 
 mod create_scope_map;
+mod dwarf_const;
 mod gdb;
 pub(crate) mod metadata;
 mod namespace;