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[CodeView] Avoid emitting empty debug globals subsection. 

In https://reviews.llvm.org/D89072 I added static const data members
to the debug subsection for globals. It skipped emitting an S_CONSTANT if it
didn't have a value, which meant the subsection could be empty.

This patch fixes the empty subsection issue.

Differential Revision: https://reviews.llvm.org/D92049
This commit is contained in:
Amy Huang 2020-11-24 11:26:14 -08:00
parent b534beabee
commit 1363dfaf31
4 changed files with 59 additions and 4 deletions
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3
lld/COFF/PDB.cpp
View File

@ -500,6 +500,9 @@ void PDBLinker::mergeSymbolRecords(TpiSource *source,
cantFail(symData.readBytes(0, symData.getLength(), symsBuffer));
SmallVector<SymbolScope, 4> scopes;
if (symsBuffer.empty())
warn("empty symbols subsection in " + file->getName());
// Iterate every symbol to check if any need to be realigned, and if so, how
// much space we need to allocate for them.
bool needsRealignment = false;

20
lld/test/COFF/empty-subsection.s Normal file
View File

@ -0,0 +1,20 @@
# REQUIRES: x86
# RUN: llvm-mc -triple=x86_64-windows-msvc -filetype=obj -o %t.obj %s
# RUN: lld-link /entry:main /debug /out:%t.exe %t.obj 2>&1 | FileCheck %s
# CHECK: warning: empty symbols subsection
.globl main
.Lfunc_begin0:
main:
xorl %eax, %eax
retq
.Lfunc_end0:
.section .debug$S,"dr"
.p2align 2
.long 4 # Debug section magic
.long 241 # Symbol subsection for globals
.long .Ltmp5-.Ltmp4 # Subsection size
.Ltmp4:
.Ltmp5:

11
llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
View File

@ -2150,10 +2150,13 @@ void CodeViewDebug::collectMemberInfo(ClassInfo &Info,
if (!DDTy->getName().empty()) {
Info.Members.push_back({DDTy, 0});
// Collect static const data members.
// Collect static const data members with values.
if ((DDTy->getFlags() & DINode::FlagStaticMember) ==
DINode::FlagStaticMember)
StaticConstMembers.push_back(DDTy);
DINode::FlagStaticMember) {
if (DDTy->getConstant() && (isa<ConstantInt>(DDTy->getConstant()) ||
isa<ConstantFP>(DDTy->getConstant())))
StaticConstMembers.push_back(DDTy);
}
return;
}
@ -3134,7 +3137,7 @@ void CodeViewDebug::emitStaticConstMemberList() {
dyn_cast_or_null<ConstantFP>(DTy->getConstant()))
Value = APSInt(CFP->getValueAPF().bitcastToAPInt(), true);
else
continue;
llvm_unreachable("cannot emit a constant without a value");
std::string QualifiedName = getFullyQualifiedName(Scope, DTy->getName());

29
llvm/test/DebugInfo/COFF/empty-globals-subsection.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: llc < %s | FileCheck %s
; The debug info contains a struct with a non-const static member.
; Check that we don't emit a symbol subsection for globals.
; CHECK-NOT: Symbol subsection for globals
; ModuleID = 'a.cpp'
source_filename = "a.cpp"
target triple = "x86_64-pc-windows-msvc19.25.28614"
define dso_local i32 @main() {
entry:
ret i32 0
}
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!8, !9}
!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
!1 = !DIFile(filename: "a.cpp", directory: "C:/path/to/test", checksumkind: CSK_MD5, checksum: "a1dbf3aabea9e8f9d1be48f60287942f")
!2 = !{}
!3 = !{!4}
!4 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !1, line: 5, size: 32, flags: DIFlagTypePassByValue | DIFlagNonTrivial, elements: !5, identifier: ".?AU?$A@J@@")
!5 = !{!6}
!6 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !4, file: !1, line: 6, baseType: !7, size: 32, flags: DIFlagStaticMember)
!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!8 = !{i32 2, !"CodeView", i32 1}
!9 = !{i32 2, !"Debug Info Version", i32 3}