Emit the DW_AT_type for a C++ static member definition

if it is more specific than the one in its DW_AT_specification.

If a static member is an array, the translation unit containing the
member definition may have a more specific type (including its length)
than TUs only seeing the class declaration. This patch adds a
DW_AT_type to the member's DW_TAG_variable in addition to the
DW_AT_specification in these cases. The member type in the
DW_AT_specification still shows the more generic type (without the
length) to avoid defeating type uniquing.

The DWARF standard discourages “duplicating” a DW_AT_type in a member
variable definition but doesn’t explicitly forbid it.  Having the more
specific type (with the array length) available is what allows the
debugger to print the contents of a static array member variable.

https://reviews.llvm.org/D26368
rdar://problem/28706946

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286302 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit bb82f0a)

Author: adrian-prantl

lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

@@ -99,6 +99,10 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
     // We need the declaration DIE that is in the static member's class.
     DIE *VariableSpecDIE = getOrCreateStaticMemberDIE(SDMDecl);
     addDIEEntry(*VariableDIE, dwarf::DW_AT_specification, *VariableSpecDIE);
+    // If the global variable's type is different from the one in the class
+    // member type, assume that it's more specific and also emit it.
+    if (GTy != DD->resolve(SDMDecl->getBaseType()))
+      addType(*VariableDIE, GTy);
   } else {
     DeclContext = GV->getScope();
     // Add name and type.

test/DebugInfo/X86/static_member_array.ll

@@ -0,0 +1,71 @@
+; RUN: %llc_dwarf %s -filetype=obj -o - | llvm-dwarfdump -debug-dump=info - | FileCheck %s
+; Generated from:
+;
+; struct A {
+;   static int fully_specified;
+;   static int smem[];
+; };
+;  
+; int A::fully_specified;
+; int A::smem[] = { 0, 1, 2, 3 };
+;
+; CHECK: DW_TAG_variable
+; CHECK-NEXT: DW_AT_specification{{.*}}"fully_specified"
+; CHECK-NOT:  DW_AT_type
+; CHECK: DW_TAG_structure_type
+; CHECK: DW_TAG_member
+; CHECK: DW_TAG_member
+; CHECK-NEXT:   DW_AT_name {{.*}} "smem"
+; CHECK-NEXT:   DW_AT_type {{.*}} {0x[[GENERIC:[0-9]+]]}
+;
+; CHECK: 0x[[GENERIC]]: DW_TAG_array_type
+; CHECK-NOT:  DW_TAG
+; CHECK-NOT:  NULL
+; CHECK: DW_TAG_subrange_type
+; CHECK-NOT:  DW_AT_count
+; CHECK:  NULL
+;
+; CHECK: DW_TAG_variable
+; CHECK-NEXT: DW_AT_specification {{.*}}"smem"
+; CHECK-NEXT: DW_AT_type {{.*}} {0x[[SPECIFIC:[0-9]+]]}
+;
+; CHECK: 0x[[SPECIFIC]]: DW_TAG_array_type
+; CHECK-NOT:  DW_TAG
+; CHECK-NOT:  NULL
+; CHECK: DW_TAG_subrange_type
+; CHECK-NOT:  DW_TAG
+; CHECK-NOT:  NULL
+; CHECK:  DW_AT_count {{.*}} (0x04)
+
+source_filename = "static_member_array.cpp"
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.12.0"
+
+@_ZN1A15fully_specifiedE = global i32 0, align 4, !dbg !0
+@_ZN1A4smemE = global [4 x i32] [i32 0, i32 1, i32 2, i32 3], align 16, !dbg !5
+
+!llvm.dbg.cu = !{!1}
+!llvm.module.flags = !{!17, !18, !19}
+!llvm.ident = !{!20}
+
+!0 = distinct !DIGlobalVariable(name: "fully_specified", linkageName: "_ZN1A15fully_specifiedE", scope: !1, file: !2, line: 7, type: !7, isLocal: false, isDefinition: true, declaration: !13)
+!1 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !2, producer: "clang version 4.0.0 (trunk 286129) (llvm/trunk 286128)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !3, globals: !4)
+!2 = !DIFile(filename: "static_member_array.cpp", directory: "/Volumes/Data/radar/28706946")
+!3 = !{}
+!4 = !{!0, !5}
+!5 = distinct !DIGlobalVariable(name: "smem", linkageName: "_ZN1A4smemE", scope: !1, file: !2, line: 8, type: !6, isLocal: false, isDefinition: true, declaration: !10)
+!6 = !DICompositeType(tag: DW_TAG_array_type, baseType: !7, size: 128, elements: !8)
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = !{!9}
+!9 = !DISubrange(count: 4)
+!10 = !DIDerivedType(tag: DW_TAG_member, name: "smem", scope: !11, file: !2, line: 4, baseType: !14, flags: DIFlagStaticMember)
+!11 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "A", file: !2, line: 1, size: 8, elements: !12, identifier: "_ZTS1A")
+!12 = !{!13, !10}
+!13 = !DIDerivedType(tag: DW_TAG_member, name: "fully_specified", scope: !11, file: !2, line: 3, baseType: !7, flags: DIFlagStaticMember)
+!14 = !DICompositeType(tag: DW_TAG_array_type, baseType: !7, elements: !15)
+!15 = !{!16}
+!16 = !DISubrange(count: -1)
+!17 = !{i32 2, !"Dwarf Version", i32 4}
+!18 = !{i32 2, !"Debug Info Version", i32 3}
+!19 = !{i32 1, !"PIC Level", i32 2}
+!20 = !{!"clang version 4.0.0 (trunk 286129) (llvm/trunk 286128)"}