feat: -Zdebug-name-table to turn debug pub sections off

`.debug_pubnames` and `.debug_pubtypes` are poorly designed and people
seldom use them. However, they take a considerable portion of size in
the final binary. This `-Zdebug-name-table` flag make it possible to
tell to LLVM stop emitting those sections.

Author: weihanglo

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -17,6 +17,7 @@ use crate::debuginfo::utils::FatPtrKind;
 use crate::llvm;
 use crate::llvm::debuginfo::{
     DIDescriptor, DIFile, DIFlags, DILexicalBlock, DIScope, DIType, DebugEmissionKind,
+    DebugNameTableKind,
 };
 use crate::value::Value;
 
@@ -877,6 +878,11 @@ pub fn build_compile_unit_di_node<'ll, 'tcx>(
     .unwrap_or_default();
     let split_name = split_name.to_str().unwrap();
     let kind = DebugEmissionKind::from_generic(tcx.sess.opts.debuginfo);
+    let debug_name_table_kind = if tcx.sess.opts.unstable_opts.debug_name_table {
+        DebugNameTableKind::Default
+    } else {
+        DebugNameTableKind::None
+    };
 
     unsafe {
         let compile_unit_file = llvm::LLVMRustDIBuilderCreateFile(
@@ -907,6 +913,7 @@ pub fn build_compile_unit_di_node<'ll, 'tcx>(
             kind,
             0,
             tcx.sess.opts.unstable_opts.split_dwarf_inlining,
+            debug_name_table_kind,
         );
 
         if tcx.sess.opts.unstable_opts.profile {

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -5,7 +5,7 @@ use super::debuginfo::{
     DIArray, DIBasicType, DIBuilder, DICompositeType, DIDerivedType, DIDescriptor, DIEnumerator,
     DIFile, DIFlags, DIGlobalVariableExpression, DILexicalBlock, DILocation, DINameSpace,
     DISPFlags, DIScope, DISubprogram, DISubrange, DITemplateTypeParameter, DIType, DIVariable,
-    DebugEmissionKind,
+    DebugEmissionKind, DebugNameTableKind,
 };
 
 use libc::{c_char, c_int, c_uint, size_t};
@@ -793,6 +793,16 @@ pub mod debuginfo {
             }
         }
     }
+
+    /// LLVMRustDebugNameTableKind
+    #[derive(Clone, Copy)]
+    #[repr(C)]
+    pub enum DebugNameTableKind {
+        Default,
+        Gnu,
+        None,
+        Apple,
+    }
 }
 
 use bitflags::bitflags;
@@ -1783,6 +1793,7 @@ extern "C" {
         kind: DebugEmissionKind,
         DWOId: u64,
         SplitDebugInlining: bool,
+        DebugNameTableKind: DebugNameTableKind,
     ) -> &'a DIDescriptor;
 
     pub fn LLVMRustDIBuilderCreateFile<'a>(

compiler/rustc_interface/src/tests.rs

@@ -749,6 +749,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(cross_crate_inline_threshold, InliningThreshold::Always);
     tracked!(debug_info_for_profiling, true);
     tracked!(debug_macros, true);
+    tracked!(debug_name_table, false);
     tracked!(dep_info_omit_d_target, true);
     tracked!(dual_proc_macros, true);
     tracked!(dwarf_version, Some(5));

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -719,6 +719,28 @@ static DICompileUnit::DebugEmissionKind fromRust(LLVMRustDebugEmissionKind Kind)
   }
 }
 
+enum class LLVMRustDebugNameTableKind {
+    Default,
+    GNU,
+    None,
+    Apple,
+};
+
+static DICompileUnit::DebugNameTableKind fromRust(LLVMRustDebugNameTableKind Kind) {
+  switch (Kind) {
+  case LLVMRustDebugNameTableKind::Default:
+    return DICompileUnit::DebugNameTableKind::Default;
+  case LLVMRustDebugNameTableKind::GNU:
+    return DICompileUnit::DebugNameTableKind::GNU;
+  case LLVMRustDebugNameTableKind::None:
+    return DICompileUnit::DebugNameTableKind::None;
+  case LLVMRustDebugNameTableKind::Apple:
+    return DICompileUnit::DebugNameTableKind::Apple;
+  default:
+    report_fatal_error("bad DebugNameTableKind.");
+  }
+}
+
 enum class LLVMRustChecksumKind {
   None,
   MD5,
@@ -795,13 +817,15 @@ extern "C" LLVMMetadataRef LLVMRustDIBuilderCreateCompileUnit(
     const char *Flags, unsigned RuntimeVer,
     const char *SplitName, size_t SplitNameLen,
     LLVMRustDebugEmissionKind Kind,
-    uint64_t DWOId, bool SplitDebugInlining) {
+    uint64_t DWOId, bool SplitDebugInlining,
+    LLVMRustDebugNameTableKind TableKind) {
   auto *File = unwrapDI<DIFile>(FileRef);
 
   return wrap(Builder->createCompileUnit(Lang, File, StringRef(Producer, ProducerLen),
                                          isOptimized, Flags, RuntimeVer,
                                          StringRef(SplitName, SplitNameLen),
-                                         fromRust(Kind), DWOId, SplitDebugInlining));
+                                         fromRust(Kind), DWOId, SplitDebugInlining,
+                                         false, fromRust(TableKind)));
 }
 
 extern "C" LLVMMetadataRef LLVMRustDIBuilderCreateFile(

compiler/rustc_session/src/options.rs

@@ -1534,6 +1534,8 @@ options! {
         "emit discriminators and other data necessary for AutoFDO"),
     debug_macros: bool = (false, parse_bool, [TRACKED],
         "emit line numbers debug info inside macros (default: no)"),
+    debug_name_table: bool = (false, parse_bool, [TRACKED],
+        "emit debug name accelerator table to facilitate name lookup in debug info (default: no)"),
     debuginfo_compression: DebugInfoCompression = (DebugInfoCompression::None, parse_debuginfo_compression, [TRACKED],
         "compress debug info sections (none, zlib, zstd, default: none)"),
     deduplicate_diagnostics: bool = (true, parse_bool, [UNTRACKED],