[llvm] DWARF: Emit `DW_AT_artificial` on artificial globals (PR #93118)

[Josh Stone via llvm-commits]

https://github.com/cuviper created https://github.com/llvm/llvm-project/pull/93118

For `DILocalVariable`, we emit `DW_AT_artificial` if the variable or its
type has `DIFlagArtificial`, but we weren't doing that for globals.
`DIGlobalVariable` doesn't have flags itself, but its type does, so we
can still propagate the artificial flag from that.

Link: https://github.com/rust-lang/rust/issues/125126


>From 7374cdc45c4c2d2fba281e5dc7d297aae1776950 Mon Sep 17 00:00:00 2001
From: Josh Stone <jistone at redhat.com>
Date: Wed, 22 May 2024 17:44:37 -0700
Subject: [PATCH] DWARF: Emit `DW_AT_artificial` on artificial globals

For `DILocalVariable`, we emit `DW_AT_artificial` if the variable or its
type has `DIFlagArtificial`, but we weren't doing that for globals.
`DIGlobalVariable` doesn't have flags itself, but its type does, so we
can still propagate the artificial flag from that.

Link: https://github.com/rust-lang/rust/issues/125126
---
 .../CodeGen/AsmPrinter/DwarfCompileUnit.cpp   |  3 ++
 .../DebugInfo/Generic/artificial-global.ll    | 41 +++++++++++++++++++
 2 files changed, 44 insertions(+)
 create mode 100644 llvm/test/DebugInfo/Generic/artificial-global.ll

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index c1e7f01f0eba5..3843b2eb0f5ff 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -200,6 +200,9 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
   else
     addGlobalName(GV->getName(), *VariableDIE, DeclContext);
 
+  if (GTy && GTy->isArtificial())
+    addFlag(*VariableDIE, dwarf::DW_AT_artificial);
+
   addAnnotation(*VariableDIE, GV->getAnnotations());
 
   if (uint32_t AlignInBytes = GV->getAlignInBytes())
diff --git a/llvm/test/DebugInfo/Generic/artificial-global.ll b/llvm/test/DebugInfo/Generic/artificial-global.ll
new file mode 100644
index 0000000000000..af7773aa3d786
--- /dev/null
+++ b/llvm/test/DebugInfo/Generic/artificial-global.ll
@@ -0,0 +1,41 @@
+; RUN: %llc_dwarf -filetype=obj -o %t < %s
+; RUN: llvm-dwarfdump %t | FileCheck %s
+
+; Make sure DIFlagArtificial on a global will emit DW_AT_artificial.
+; (This happens through its type, because DIGlobalVariable doesn't take flags.)
+
+;CHECK: DW_TAG_variable
+;CHECK-NEXT: DW_AT_name      ("<i32 as _>::{vtable}")
+;CHECK-NEXT: DW_AT_type      (0x{{[0-9a-f]+}} "<i32 as _>::{vtable_type}")
+;CHECK-NEXT: DW_AT_artificial        (true)
+;CHECK-NEXT: DW_AT_location  (DW_OP_addr 0x0)
+
+ at vtable.0 = hidden constant <{ ptr, [16 x i8] }> <{ ptr @"_ZN4core3ptr24drop_in_place$LT$i32$GT$17hb6decb5d90d320b6E", [16 x i8] c"\04\00\00\00\00\00\00\00\04\00\00\00\00\00\00\00" }>, align 8, !dbg !0
+
+; Function Attrs: inlinehint nonlazybind uwtable
+declare hidden void @"_ZN4core3ptr24drop_in_place$LT$i32$GT$17hb6decb5d90d320b6E"(ptr align 4) unnamed_addr #0
+
+attributes #0 = { inlinehint nonlazybind uwtable "probe-stack"="inline-asm" "target-cpu"="x86-64" }
+
+!llvm.module.flags = !{!13, !14, !15, !16}
+!llvm.dbg.cu = !{!17}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "<i32 as _>::{vtable}", scope: null, file: !2, type: !3, isLocal: true, isDefinition: true)
+!2 = !DIFile(filename: "<unknown>", directory: "")
+!3 = !DICompositeType(tag: DW_TAG_structure_type, name: "<i32 as _>::{vtable_type}", file: !2, size: 192, align: 64, flags: DIFlagArtificial, elements: !4, vtableHolder: !11, templateParams: !12, identifier: "c43795a3e66ad62fad3e5bb73c25fc9")
+!4 = !{!5, !8, !10}
+!5 = !DIDerivedType(tag: DW_TAG_member, name: "drop_in_place", scope: !3, file: !2, baseType: !6, size: 64, align: 64)
+!6 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "*const ()", baseType: !7, size: 64, align: 64, dwarfAddressSpace: 0)
+!7 = !DIBasicType(name: "()", encoding: DW_ATE_unsigned)
+!8 = !DIDerivedType(tag: DW_TAG_member, name: "size", scope: !3, file: !2, baseType: !9, size: 64, align: 64, offset: 64)
+!9 = !DIBasicType(name: "usize", size: 64, encoding: DW_ATE_unsigned)
+!10 = !DIDerivedType(tag: DW_TAG_member, name: "align", scope: !3, file: !2, baseType: !9, size: 64, align: 64, offset: 128)
+!11 = !DIBasicType(name: "i32", size: 32, encoding: DW_ATE_signed)
+!12 = !{}
+!13 = !{i32 8, !"PIC Level", i32 2}
+!14 = !{i32 2, !"RtLibUseGOT", i32 1}
+!15 = !{i32 2, !"Dwarf Version", i32 4}
+!16 = !{i32 2, !"Debug Info Version", i32 3}
+!17 = distinct !DICompileUnit(language: DW_LANG_Rust, file: !2, isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, globals: !18)
+!18 = !{!0}