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[DebugInfo] Change handling of structured bindings of bitfields #94632

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Merged
merged 2 commits into from
Jun 17, 2024
Merged

[DebugInfo] Change handling of structured bindings of bitfields #94632

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c490a8c
[DebugInfo] Change handling of structured bindings of bitfields
john-brawn-arm Mar 14, 2024
050d8cf
Merge branch 'main' into bitfield_debug_info_extract_bits_clang
john-brawn-arm Jun 17, 2024
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68 changes: 25 additions & 43 deletions clang/lib/CodeGen/CGDebugInfo.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4874,40 +4874,6 @@ llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const VarDecl *VD,
return D;
}

llvm::DIType *CGDebugInfo::CreateBindingDeclType(const BindingDecl *BD) {
llvm::DIFile *Unit = getOrCreateFile(BD->getLocation());

// If the declaration is bound to a bitfield struct field, its type may have a
// size that is different from its deduced declaration type's.
if (const MemberExpr *ME = dyn_cast<MemberExpr>(BD->getBinding())) {
if (const FieldDecl *FD = dyn_cast<FieldDecl>(ME->getMemberDecl())) {
if (FD->isBitField()) {
ASTContext &Context = CGM.getContext();
const CGRecordLayout &RL =
CGM.getTypes().getCGRecordLayout(FD->getParent());
const CGBitFieldInfo &Info = RL.getBitFieldInfo(FD);

// Find an integer type with the same bitwidth as the bitfield size. If
// no suitable type is present in the target, give up on producing debug
// information as it would be wrong. It is certainly possible to produce
// correct debug info, but the logic isn't currently implemented.
uint64_t BitfieldSizeInBits = Info.Size;
QualType IntTy =
Context.getIntTypeForBitwidth(BitfieldSizeInBits, Info.IsSigned);
if (IntTy.isNull())
return nullptr;
Qualifiers Quals = BD->getType().getQualifiers();
QualType FinalTy = Context.getQualifiedType(IntTy, Quals);
llvm::DIType *Ty = getOrCreateType(FinalTy, Unit);
assert(Ty);
return Ty;
}
}
}

return getOrCreateType(BD->getType(), Unit);
}

llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const BindingDecl *BD,
llvm::Value *Storage,
std::optional<unsigned> ArgNo,
Expand All @@ -4922,7 +4888,8 @@ llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const BindingDecl *BD,
if (isa<DeclRefExpr>(BD->getBinding()))
return nullptr;

llvm::DIType *Ty = CreateBindingDeclType(BD);
llvm::DIFile *Unit = getOrCreateFile(BD->getLocation());
llvm::DIType *Ty = getOrCreateType(BD->getType(), Unit);

// If there is no debug info for this type then do not emit debug info
// for this variable.
Expand All @@ -4948,7 +4915,6 @@ llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const BindingDecl *BD,
unsigned Column = getColumnNumber(BD->getLocation());
StringRef Name = BD->getName();
auto *Scope = cast<llvm::DIScope>(LexicalBlockStack.back());
llvm::DIFile *Unit = getOrCreateFile(BD->getLocation());
// Create the descriptor for the variable.
llvm::DILocalVariable *D = DBuilder.createAutoVariable(
Scope, Name, Unit, Line, Ty, CGM.getLangOpts().Optimize,
Expand All @@ -4962,13 +4928,29 @@ llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const BindingDecl *BD,
const ASTRecordLayout &layout =
CGM.getContext().getASTRecordLayout(parent);
const uint64_t fieldOffset = layout.getFieldOffset(fieldIndex);

if (fieldOffset != 0) {
// Currently if the field offset is not a multiple of byte, the produced
// location would not be accurate. Therefore give up.
if (fieldOffset % CGM.getContext().getCharWidth() != 0)
return nullptr;

if (FD->isBitField()) {
const CGRecordLayout &RL =
CGM.getTypes().getCGRecordLayout(FD->getParent());
const CGBitFieldInfo &Info = RL.getBitFieldInfo(FD);
// Use DW_OP_plus_uconst to adjust to the start of the bitfield
// storage.
if (!Info.StorageOffset.isZero()) {
Expr.push_back(llvm::dwarf::DW_OP_plus_uconst);
Expr.push_back(Info.StorageOffset.getQuantity());
}
// Use LLVM_extract_bits to extract the appropriate bits from this
// bitfield.
Expr.push_back(Info.IsSigned
? llvm::dwarf::DW_OP_LLVM_extract_bits_sext
: llvm::dwarf::DW_OP_LLVM_extract_bits_zext);
Expr.push_back(Info.Offset);
// If we have an oversized bitfield then the value won't be more than
// the size of the type.
const uint64_t TypeSize = CGM.getContext().getTypeSize(BD->getType());
Expr.push_back(std::min((uint64_t)Info.Size, TypeSize));
} else if (fieldOffset != 0) {
assert(fieldOffset % CGM.getContext().getCharWidth() == 0 &&
"Unexpected non-bitfield with non-byte-aligned offset");
Expr.push_back(llvm::dwarf::DW_OP_plus_uconst);
Expr.push_back(
CGM.getContext().toCharUnitsFromBits(fieldOffset).getQuantity());
Expand Down
3 changes: 0 additions & 3 deletions clang/lib/CodeGen/CGDebugInfo.h
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Original file line number Diff line number Diff line change
Expand Up @@ -338,9 +338,6 @@ class CGDebugInfo {
llvm::DIScope *RecordTy,
const RecordDecl *RD);

/// Create type for binding declarations.
llvm::DIType *CreateBindingDeclType(const BindingDecl *BD);

/// Create an anonnymous zero-size separator for bit-field-decl if needed on
/// the target.
llvm::DIDerivedType *createBitFieldSeparatorIfNeeded(
Expand Down
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