[llvm] r313203 - [codeview] VLAs and unsized arrays should use a size of zero

Wed Sep 13 15:01:44 PDT 2017

On Wed, Sep 13, 2017 at 2:54 PM, Reid Kleckner via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: rnk
> Date: Wed Sep 13 14:54:20 2017
> New Revision: 313203
>
> URL: http://llvm.org/viewvc/llvm-project?rev=313203&view=rev
> Log:
> [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
>
> Added:
>     llvm/trunk/test/DebugInfo/COFF/types-array-unsized.ll
> Modified:
>     llvm/trunk/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
>     llvm/trunk/test/DebugInfo/COFF/types-array-advanced.ll
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/
> CodeGen/AsmPrinter/CodeViewDebug.cpp?rev=313203&
> r1=313202&r2=313203&view=diff
> ============================================================
> ==================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp Wed Sep 13
> 14:54:20 2017
> @@ -1277,11 +1277,12 @@ TypeIndex CodeViewDebug::lowerTypeArray(
>             "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.
>

I think this FIXME can go away.

>      if (Count == -1)
> -      Count = 1;
> +      Count = 0;
>
>      // Update the element size and element type index for subsequent
> subranges.
>      ElementSize *= Count;
>
> Modified: llvm/trunk/test/DebugInfo/COFF/types-array-advanced.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/
> DebugInfo/COFF/types-array-advanced.ll?rev=313203&r1=
> 313202&r2=313203&view=diff
> ============================================================
> ==================
> --- llvm/trunk/test/DebugInfo/COFF/types-array-advanced.ll (original)
> +++ llvm/trunk/test/DebugInfo/COFF/types-array-advanced.ll Wed Sep 13
> 14:54:20 2017
> @@ -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) {
>
> Added: llvm/trunk/test/DebugInfo/COFF/types-array-unsized.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/
> DebugInfo/COFF/types-array-unsized.ll?rev=313203&view=auto
> ============================================================
> ==================
> --- llvm/trunk/test/DebugInfo/COFF/types-array-unsized.ll (added)
> +++ llvm/trunk/test/DebugInfo/COFF/types-array-unsized.ll Wed Sep 13
> 14:54:20 2017
> @@ -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 at Foo@@2QBDB+0x0
> +; CHECK-NEXT:       Type: [[ARRAY_COMPLETE]]
> +; CHECK-NEXT:       DisplayName: str
> +; CHECK-NEXT:       LinkageName: ?str at 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 at 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 at 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 "}
>
>
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