[WIP][DebugInfo][AsmPrinter] Emit the DW_AT_LLVM_lambda_name

[djtodoro]

Summary

See D77799.

llvm/include/llvm/BinaryFormat/Dwarf.def

 HANDLE_DW_AT(0x3b31, BORLAND_closure, 0, BORLAND)
 // LLVM project extensions.
 HANDLE_DW_AT(0x3e00, LLVM_include_path, 0, LLVM)
 HANDLE_DW_AT(0x3e01, LLVM_config_macros, 0, LLVM)
 HANDLE_DW_AT(0x3e02, LLVM_sysroot, 0, LLVM)
 HANDLE_DW_AT(0x3e03, LLVM_tag_offset, 0, LLVM)
 // The missing numbers here are reserved for ptrauth support.
 HANDLE_DW_AT(0x3e07, LLVM_apinotes, 0, APPLE)
+// Experimental lamda name attribute.
+HANDLE_DW_AT(0x3e08, LLVM_lambda_name, 0, LLVM)
 
 // Apple extensions.
 
 HANDLE_DW_AT(0x3fe1, APPLE_optimized, 0, APPLE)
 HANDLE_DW_AT(0x3fe2, APPLE_flags, 0, APPLE)
 HANDLE_DW_AT(0x3fe3, APPLE_isa, 0, APPLE)
 HANDLE_DW_AT(0x3fe4, APPLE_block, 0, APPLE)
 HANDLE_DW_AT(0x3fe5, APPLE_major_runtime_vers, 0, APPLE)

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCDwarf.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MachineLocation.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetLoweringObjectFile.h"
+#include "llvm/Target/TargetMachine.h"
 #include <cassert>
 #include <cstdint>
 #include <string>
 #include <utility>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "dwarfdebug"
if (auto *SPDecl = SP->getDeclaration()) {
 
     if (SP->getLine() != SPDecl->getLine())
       addUInt(SPDie, dwarf::DW_AT_decl_line, None, SP->getLine());
   }
 
   // Add function template parameters.
   addTemplateParams(SPDie, SP->getTemplateParams());
 
-  // Add the linkage name if we have one and it isn't in the Decl.
+  // Use either the lambda or linkage name.
+  // The lambda name is supported only within LLDB debugger.
+  if (!SP->getLambda().empty() &&
+      Asm->TM.Options.DebuggerTuning == DebuggerKind::LLDB) {
+    // Add the lambda name.
+    addString(SPDie, dwarf::DW_AT_LLVM_lambda_name, SP->getLambda());
+  } else {
     StringRef LinkageName = SP->getLinkageName();
     assert(((LinkageName.empty() || DeclLinkageName.empty()) ||
             LinkageName == DeclLinkageName) &&
           "decl has a linkage name and it is different");
     if (DeclLinkageName.empty() &&
         // Always emit it for abstract subprograms.
         (DD->useAllLinkageNames() || DU->getAbstractSPDies().lookup(SP)))
       addLinkageName(SPDie, LinkageName);
+  }
 
   if (!DeclDie)
     return false;
 
   // Refer to the function declaration where all the other attributes will be
   // found.
   addDIEEntry(SPDie, dwarf::DW_AT_specification, *DeclDie);
   return true;

llvm/test/DebugInfo/X86/lambda_name.ll

+;; Check the DW_AT_LLVM_lambda_name attribute.
+
+; RUN: llc %s -mtriple=x86_64-pc-linux-gnu --debugger-tune=lldb -o -| FileCheck %s
+
+; CHECK: DW_AT_LLVM_lambda_name
+
+; ModuleID = 'test.cpp'
+source_filename = "test.cpp"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%class.anon = type { i8 }
+
+; Function Attrs: uwtable
+define dso_local i32 @_Z3fn2v() local_unnamed_addr !dbg !12 {
+entry:
+  call void @llvm.dbg.value(metadata i32 0, metadata !18, metadata !DIExpression()), !dbg !20
+  call void @llvm.dbg.value(metadata %class.anon* undef, metadata !21, metadata !DIExpression()), !dbg !34
+  call void @llvm.dbg.value(metadata i32 0, metadata !32, metadata !DIExpression()), !dbg !34
+  tail call void @_Z2fni(i32 0), !dbg !37
+  call void @llvm.dbg.value(metadata i32 1, metadata !18, metadata !DIExpression()), !dbg !20
+  call void @llvm.dbg.value(metadata i32 1, metadata !32, metadata !DIExpression()), !dbg !34
+  tail call void @_Z2fni(i32 1), !dbg !37
+  call void @llvm.dbg.value(metadata i32 2, metadata !18, metadata !DIExpression()), !dbg !20
+  call void @llvm.dbg.value(metadata i32 2, metadata !32, metadata !DIExpression()), !dbg !34
+  tail call void @_Z2fni(i32 2), !dbg !37
+  call void @llvm.dbg.value(metadata i32 3, metadata !18, metadata !DIExpression()), !dbg !20
+  call void @llvm.dbg.value(metadata i32 3, metadata !32, metadata !DIExpression()), !dbg !34
+  tail call void @_Z2fni(i32 3), !dbg !37
+  call void @llvm.dbg.value(metadata i32 4, metadata !18, metadata !DIExpression()), !dbg !20
+  call void @llvm.dbg.value(metadata i32 4, metadata !32, metadata !DIExpression()), !dbg !34
+  tail call void @_Z2fni(i32 4), !dbg !37
+  call void @llvm.dbg.value(metadata i32 5, metadata !18, metadata !DIExpression()), !dbg !20
+  ret i32 0, !dbg !38
+}
+
+declare !dbg !4 dso_local void @_Z2fni(i32) local_unnamed_addr
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!8, !9, !10}
+!llvm.ident = !{!11}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 11.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{}
+!3 = !{!4}
+!4 = !DISubprogram(name: "fn", linkageName: "_Z2fni", scope: !1, file: !1, line: 1, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+!5 = !DISubroutineType(types: !6)
+!6 = !{null, !7}
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = !{i32 7, !"Dwarf Version", i32 4}
+!9 = !{i32 2, !"Debug Info Version", i32 3}
+!10 = !{i32 1, !"wchar_size", i32 4}
+!11 = !{!"clang version 11.0.0"}
+!12 = distinct !DISubprogram(name: "fn2", linkageName: "_Z3fn2v", scope: !1, file: !1, line: 3, type: !13, scopeLine: 3, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
+!13 = !DISubroutineType(types: !14)
+!14 = !{!7}
+!15 = !{!16, !18}
+!16 = !DILocalVariable(name: "doSomething", scope: !12, file: !1, line: 4, type: !17)
+!17 = distinct !DICompositeType(tag: DW_TAG_class_type, scope: !12, file: !1, line: 4, size: 8, flags: DIFlagTypePassByValue | DIFlagNonTrivial, elements: !2)
+!18 = !DILocalVariable(name: "i", scope: !19, file: !1, line: 8, type: !7)
+!19 = distinct !DILexicalBlock(scope: !12, file: !1, line: 8, column: 3)
+!20 = !DILocation(line: 0, scope: !19)
+!21 = !DILocalVariable(name: "this", arg: 1, scope: !22, type: !33, flags: DIFlagArtificial | DIFlagObjectPointer)
+!22 = distinct !DISubprogram(name: "operator()", linkageName: "_ZZ3fn2vENK3$_0clEi", scope: !17, file: !1, line: 4, type: !23, scopeLine: 4, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !0, declaration: !27, retainedNodes: !31, lambda: "doSomething")
+!23 = !DISubroutineType(types: !24)
+!24 = !{null, !25, !7}
+!25 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !26, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!26 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !17)
+!27 = !DISubprogram(name: "operator()", scope: !17, file: !1, line: 4, type: !28, scopeLine: 4, flags: DIFlagPublic | DIFlagPrototyped, spFlags: DISPFlagOptimized)
+!28 = !DISubroutineType(types: !29)
+!29 = !{!30, !25, !7}
+!30 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "auto")
+!31 = !{!21, !32}
+!32 = !DILocalVariable(name: "num", arg: 2, scope: !22, file: !1, line: 4, type: !7)
+!33 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !26, size: 64)
+!34 = !DILocation(line: 0, scope: !22, inlinedAt: !35)
+!35 = distinct !DILocation(line: 9, column: 5, scope: !36)
+!36 = distinct !DILexicalBlock(scope: !19, file: !1, line: 8, column: 3)
+!37 = !DILocation(line: 5, column: 5, scope: !22, inlinedAt: !35)
+!38 = !DILocation(line: 11, column: 3, scope: !12)