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[DebugInfo] Add DW_AT_byte_size to vectors

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Summary:
This patch adds the DW_AT_byte_size dwarf attribute to vectors.
This fixes PR21924

LLVM will round a vector up to the next alignable address, which can result in
the vector's representation in the object file being larger than what the
debugger will calculate via NumberOfElements * ElementSize. In such a case calling sizeof(MyVec) in the source will result in a different value than what a debugger might present. This situation can occur because LLVM permits non-power of two 'vector_size' attributes.

Reviewers: echristo, dexonsmith, aprantl

Reviewed By: aprantl

Subscribers: probinson, aprantl, llvm-commits, JDevlieghere

Tags: #debug-info

Differential Revision: https://reviews.llvm.org/D44048

llvm-svn: 327072
This commit is contained in:
Matt Davis 2018-03-08 22:22:26 +00:00
parent 9d97b29d2f
commit fe25df29a1
2 changed files with 79 additions and 1 deletions
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33
lib/CodeGen/AsmPrinter/DwarfUnit.cpp
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@ -1408,9 +1408,40 @@ DIE *DwarfUnit::getIndexTyDie() {
return IndexTyDie;
}
/// Returns true if the vector's size differs from the sum of sizes of elements
/// the user specified. This can occur if the vector has been rounded up to
/// fit memory alignment constraints.
static bool hasVectorBeenPadded(const DICompositeType *CTy) {
assert(CTy && CTy->isVector() && "Composite type is not a vector");
const uint64_t ActualSize = CTy->getSizeInBits();
// Obtain the size of each element in the vector.
DIType *BaseTy = CTy->getBaseType().resolve();
assert(BaseTy && "Unknown vector element type.");
const uint64_t ElementSize = BaseTy->getSizeInBits();
// Locate the number of elements in the vector.
const DINodeArray Elements = CTy->getElements();
assert(Elements.size() == 1 &&
Elements[0]->getTag() == dwarf::DW_TAG_subrange_type &&
"Invalid vector element array, expected one element of type subrange");
const auto Subrange = cast<DISubrange>(Elements[0]);
const auto CI = Subrange->getCount().get<ConstantInt *>();
const int32_t NumVecElements = CI->getSExtValue();
// Ensure we found the element count and that the actual size is wide
// enough to contain the requested size.
assert(ActualSize >= (NumVecElements * ElementSize) && "Invalid vector size");
return ActualSize != (NumVecElements * ElementSize);
}
void DwarfUnit::constructArrayTypeDIE(DIE &Buffer, const DICompositeType *CTy) {
if (CTy->isVector())
if (CTy->isVector()) {
addFlag(Buffer, dwarf::DW_AT_GNU_vector);
if (hasVectorBeenPadded(CTy))
addUInt(Buffer, dwarf::DW_AT_byte_size, None,
CTy->getSizeInBits() / CHAR_BIT);
}
// Emit the element type.
addType(Buffer, resolve(CTy->getBaseType()));

47
test/DebugInfo/X86/dbg-vector-size.ll Normal file
View File

@ -0,0 +1,47 @@
; RUN: llc < %s -filetype=obj | llvm-dwarfdump -v -debug-info - | FileCheck %s
;
; CHECK: DW_TAG_array_type
; CHECK-NEXT: DW_AT_GNU_vector [DW_FORM_flag_present] (true)
; CHECK-NEXT: DW_AT_byte_size [DW_FORM_data1] (0x20)
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
define dso_local void @test() !dbg !9 {
%1 = alloca <6 x float>, align 32
call void @llvm.dbg.declare(metadata <6 x float>* %1, metadata !13, metadata !DIExpression()), !dbg !19
%2 = bitcast <6 x float>* %1 to i8*, !dbg !20
call void @foo(i8* %2), !dbg !21
ret void, !dbg !22
}
declare void @llvm.dbg.declare(metadata, metadata, metadata)
declare dso_local void @foo(i8*)
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!5, !6, !7}
!llvm.ident = !{!8}
!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3)
!1 = !DIFile(filename: "small.c", directory: "/dbg/info")
!2 = !{}
!3 = !{!4}
!4 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
!5 = !{i32 2, !"Dwarf Version", i32 4}
!6 = !{i32 2, !"Debug Info Version", i32 3}
!7 = !{i32 1, !"wchar_size", i32 4}
!8 = !{!"clang"}
!9 = distinct !DISubprogram(name: "test", scope: !10, file: !10, line: 3, type: !11, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
!10 = !DIFile(filename: "./small.c", directory: "/dbg/info")
!11 = !DISubroutineType(types: !12)
!12 = !{null}
!13 = !DILocalVariable(name: "v01", scope: !9, file: !10, line: 4, type: !14)
!14 = !DIDerivedType(tag: DW_TAG_typedef, name: "vec6f", file: !10, line: 1, baseType: !15)
!15 = !DICompositeType(tag: DW_TAG_array_type, baseType: !16, size: 256, flags: DIFlagVector, elements: !17)
!16 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
!17 = !{!18}
!18 = !DISubrange(count: 6)
!19 = !DILocation(line: 4, column: 9, scope: !9)
!20 = !DILocation(line: 5, column: 7, scope: !9)
!21 = !DILocation(line: 5, column: 3, scope: !9)
!22 = !DILocation(line: 6, column: 1, scope: !9)