BPF: emit BTF_KIND_DECL_TAG for typedef types

[yonghong-song]

Summary

If a typedef type has attribute((btf_decl_tag("str"))) with
bpf target, emit BTF_KIND_DECL_TAG for that type in the BTF.

llvm/lib/Target/BPF/BTFDebug.cpp

if (CheckPointer && SeenPointer) {
     }
   }
 
   if (Tag == dwarf::DW_TAG_pointer_type || Tag == dwarf::DW_TAG_typedef ||
       Tag == dwarf::DW_TAG_const_type || Tag == dwarf::DW_TAG_volatile_type ||
       Tag == dwarf::DW_TAG_restrict_type) {
     auto TypeEntry = std::make_unique<BTFTypeDerived>(DTy, Tag, false);
     TypeId = addType(std::move(TypeEntry), DTy);
+    if (Tag == dwarf::DW_TAG_typedef)
+      processDeclAnnotations(DTy->getAnnotations(), TypeId, -1);
   } else if (Tag != dwarf::DW_TAG_member) {
     return;
   }
 
   // Visit base type of pointer, typedef, const, volatile, restrict or
   // struct/union member.
   uint32_t TempTypeId = 0;
   if (Tag == dwarf::DW_TAG_member)

llvm/test/CodeGen/BPF/BTF/tag-typedef.ll

+; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+; RUN: llc -march=bpfeb -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+
+; Source code:
+;   #define __tag1 __attribute__((btf_decl_tag("tag1")))
+;   typedef struct { int a; } __s __tag1;
+;   typedef unsigned * __u __tag1;
+;   __s a;
+;   __u u;
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm t.c
+
+%struct.__s = type { i32 }
+
+@a = dso_local local_unnamed_addr global %struct.__s zeroinitializer, align 4, !dbg !0
+@u = dso_local local_unnamed_addr global i32* null, align 8, !dbg !5
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!17, !18, !19, !20}
+!llvm.ident = !{!21}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "a", scope: !2, file: !3, line: 4, type: !12, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 14.0.0 (https://github.com/llvm/llvm-project.git 219b26fbcd70273ddfd4ead9387f7c69b7eb4570)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "t.c", directory: "/tmp/home/yhs/work/tests/llvm/btf_tag")
+!4 = !{!0, !5}
+!5 = !DIGlobalVariableExpression(var: !6, expr: !DIExpression())
+!6 = distinct !DIGlobalVariable(name: "u", scope: !2, file: !3, line: 5, type: !7, isLocal: false, isDefinition: true)
+!7 = !DIDerivedType(tag: DW_TAG_typedef, name: "__u", file: !3, line: 3, baseType: !8, annotations: !10)
+!8 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64)
+!9 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+!10 = !{!11}
+!11 = !{!"btf_decl_tag", !"tag1"}
+!12 = !DIDerivedType(tag: DW_TAG_typedef, name: "__s", file: !3, line: 2, baseType: !13, annotations: !10)
+!13 = distinct !DICompositeType(tag: DW_TAG_structure_type, file: !3, line: 2, size: 32, elements: !14)
+!14 = !{!15}
+!15 = !DIDerivedType(tag: DW_TAG_member, name: "a", scope: !13, file: !3, line: 2, baseType: !16, size: 32)
+!16 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!17 = !{i32 7, !"Dwarf Version", i32 4}
+!18 = !{i32 2, !"Debug Info Version", i32 3}
+!19 = !{i32 1, !"wchar_size", i32 4}
+!20 = !{i32 7, !"frame-pointer", i32 2}
+!21 = !{!"clang version 14.0.0 (https://github.com/llvm/llvm-project.git 219b26fbcd70273ddfd4ead9387f7c69b7eb4570)"}
+
+; CHECK:             .long   1                               # BTF_KIND_TYPEDEF(id = 1)
+; CHECK-NEXT:        .long   134217728                       # 0x8000000
+; CHECK-NEXT:        .long   3
+; CHECK-NEXT:        .long   5                               # BTF_KIND_DECL_TAG(id = 2)
+; CHECK-NEXT:        .long   285212672                       # 0x11000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   4294967295
+; CHECK-NEXT:        .long   0                               # BTF_KIND_STRUCT(id = 3)
+; CHECK-NEXT:        .long   67108865                        # 0x4000001
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   10
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   0                               # 0x0
+; CHECK-NEXT:        .long   12                              # BTF_KIND_INT(id = 4)
+; CHECK-NEXT:        .long   16777216                        # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   16777248                        # 0x1000020
+; CHECK-NEXT:        .long   10                              # BTF_KIND_VAR(id = 5)
+; CHECK-NEXT:        .long   234881024                       # 0xe000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   16                              # BTF_KIND_TYPEDEF(id = 6)
+; CHECK-NEXT:        .long   134217728                       # 0x8000000
+; CHECK-NEXT:        .long   8
+; CHECK-NEXT:        .long   5                               # BTF_KIND_DECL_TAG(id = 7)
+; CHECK-NEXT:        .long   285212672                       # 0x11000000
+; CHECK-NEXT:        .long   6
+; CHECK-NEXT:        .long   4294967295
+; CHECK-NEXT:        .long   0                               # BTF_KIND_PTR(id = 8)
+; CHECK-NEXT:        .long   33554432                        # 0x2000000
+; CHECK-NEXT:        .long   9
+; CHECK-NEXT:        .long   20                              # BTF_KIND_INT(id = 9)
+; CHECK-NEXT:        .long   16777216                        # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   32                              # 0x20
+
+; CHECK:        .ascii  "__s"                           # string offset=1
+; CHECK:        .ascii  "tag1"                          # string offset=5
+; CHECK:        .byte   97                              # string offset=10
+; CHECK:        .ascii  "int"                           # string offset=12
+; CHECK:        .ascii  "__u"                           # string offset=16
+; CHECK:        .ascii  "unsigned int"                  # string offset=20
+