[codeview] VLAs and unsized arrays should use a size of zero

Previously we used a size of '1' for VLAs because we weren't sure what
MSVC did. However, MSVC does support declaring an array without a size,
for which it emits an array type with a size of zero. Clang emits the
same DI metadata for VLAs and arrays without bound, so we would describe
arrays without bound as having one element. This lead to Microsoft
debuggers only printing a single element.

Emitting a size of zero appears to cause these debuggers to search the
symbol information to find a definition of the variable with accurate
array bounds.

Fixes http://crbug.com/763580

llvm-svn: 313203

3 files changed, 89 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index ed2dfa6906f..6eba00be00e 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -1277,11 +1277,12 @@ TypeIndex CodeViewDebug::lowerTypeArray(const DICompositeType *Ty) {
            "codeview doesn't support subranges with lower bounds");
     int64_t Count = Subrange->getCount();
 
-    // Variable Length Array (VLA) has Count equal to '-1'.
-    // Replace with Count '1', assume it is the minimum VLA length.
+    // Variable length arrays and forward declarations of arrays without a size
+    // use a count of -1. Emit a count (and overall size) or zero in these cases
+    // to match what MSVC does for array declarations with no count.
     // FIXME: Make front-end support VLA subrange and emit LF_DIMVARLU.
     if (Count == -1)
-      Count = 1;
+      Count = 0;
 
     // Update the element size and element type index for subsequent subranges.
     ElementSize *= Count;
diff --git a/llvm/test/DebugInfo/COFF/types-array-advanced.ll b/llvm/test/DebugInfo/COFF/types-array-advanced.ll
index a2e7c19b74c..f13aa6ac853 100644
--- a/llvm/test/DebugInfo/COFF/types-array-advanced.ll
+++ b/llvm/test/DebugInfo/COFF/types-array-advanced.ll
@@ -47,7 +47,7 @@
 ; CHECK:     TypeLeafKind: LF_ARRAY (0x1503)
 ; CHECK:     ElementType: int (0x74)
 ; CHECK:     IndexType: unsigned long (0x22)
-; CHECK:     SizeOf: 4
+; CHECK:     SizeOf: 0
 ; CHECK:     Name: 
 ; CHECK:   }
 ; CHECK:   Pointer (0x1004) {
diff --git a/llvm/test/DebugInfo/COFF/types-array-unsized.ll b/llvm/test/DebugInfo/COFF/types-array-unsized.ll
new file mode 100644
index 00000000000..694e0a77b2c
--- /dev/null
+++ b/llvm/test/DebugInfo/COFF/types-array-unsized.ll
@@ -0,0 +1,84 @@
+; RUN: llc -filetype=obj < %s | llvm-readobj -codeview | FileCheck %s
+
+; We should emit two array types: one used to describe the static data member,
+; and the other used by the S_GDATA32 for the definition.
+
+; C++ source:
+; struct Foo {
+;   static const char str[];
+; };
+; const char Foo::str[] = "asdf";
+; Foo f; // FIXME: only needed to force emit 'Foo'
+
+; CHECK:      CodeViewTypes [
+; CHECK:        Array ([[ARRAY_COMPLETE:0x.*]]) {
+; CHECK-NEXT:     TypeLeafKind: LF_ARRAY (0x1503)
+; CHECK-NEXT:     ElementType: const char ({{.*}})
+; CHECK-NEXT:     IndexType: unsigned __int64 (0x23)
+; CHECK-NEXT:     SizeOf: 5
+; CHECK-NEXT:     Name: 
+; CHECK-NEXT:   }
+; CHECK:        Array ([[ARRAY_FWD:0x.*]]) {
+; CHECK-NEXT:     TypeLeafKind: LF_ARRAY (0x1503)
+; CHECK-NEXT:     ElementType: const char ({{.*}})
+; CHECK-NEXT:     IndexType: unsigned __int64 (0x23)
+; CHECK-NEXT:     SizeOf: 0
+; CHECK-NEXT:     Name: 
+; CHECK-NEXT:   }
+; CHECK:        FieldList (0x1004) {
+; CHECK-NEXT:     TypeLeafKind: LF_FIELDLIST (0x1203)
+; CHECK-NEXT:     StaticDataMember {
+; CHECK-NEXT:       TypeLeafKind: LF_STMEMBER (0x150E)
+; CHECK-NEXT:       AccessSpecifier: Public (0x3)
+; CHECK-NEXT:       Type: [[ARRAY_FWD]]
+; CHECK-NEXT:       Name: str
+; CHECK-NEXT:     }
+; CHECK-NEXT:   }
+; CHECK:      ]
+
+; CHECK:          GlobalData {
+; CHECK-NEXT:       Kind: S_GDATA32 (0x110D)
+; CHECK-NEXT:       DataOffset: ?str@Foo@@2QBDB+0x0
+; CHECK-NEXT:       Type: [[ARRAY_COMPLETE]]
+; CHECK-NEXT:       DisplayName: str
+; CHECK-NEXT:       LinkageName: ?str@Foo@@2QBDB
+; CHECK-NEXT:     }
+
+; ModuleID = 't.cpp'
+source_filename = "t.cpp"
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.0.24215"
+
+%struct.Foo = type { i8 }
+
+@"\01?str@Foo@@2QBDB" = constant [5 x i8] c"asdf\00", align 1, !dbg !0
+@"\01?f@@3UFoo@@A" = global %struct.Foo zeroinitializer, align 1, !dbg !6
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!19, !20, !21, !22}
+!llvm.ident = !{!23}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "str", linkageName: "\01?str@Foo@@2QBDB", scope: !2, file: !3, line: 4, type: !16, isLocal: false, isDefinition: true, declaration: !10)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 6.0.0 ", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!3 = !DIFile(filename: "t.cpp", directory: "C:\5Csrc\5Cllvm-project\5Cbuild", checksumkind: CSK_MD5, checksum: "15aa843c5a80301928caf03e71f87a54")
+!4 = !{}
+!5 = !{!0, !6}
+!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = distinct !DIGlobalVariable(name: "f", linkageName: "\01?f@@3UFoo@@A", scope: !2, file: !3, line: 5, type: !8, isLocal: false, isDefinition: true)
+!8 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Foo", file: !3, line: 1, size: 8, elements: !9, identifier: ".?AUFoo@@")
+!9 = !{!10}
+!10 = !DIDerivedType(tag: DW_TAG_member, name: "str", scope: !8, file: !3, line: 2, baseType: !11, flags: DIFlagStaticMember)
+!11 = !DICompositeType(tag: DW_TAG_array_type, baseType: !12, elements: !14)
+!12 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !13)
+!13 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!14 = !{!15}
+!15 = !DISubrange(count: -1)
+!16 = !DICompositeType(tag: DW_TAG_array_type, baseType: !12, size: 40, elements: !17)
+!17 = !{!18}
+!18 = !DISubrange(count: 5)
+!19 = !{i32 2, !"CodeView", i32 1}
+!20 = !{i32 2, !"Debug Info Version", i32 3}
+!21 = !{i32 1, !"wchar_size", i32 2}
+!22 = !{i32 7, !"PIC Level", i32 2}
+!23 = !{!"clang version 6.0.0 "}