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[Clang][DebugInfo] Emit narrower base types for structured binding de…
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…clarations that bind to struct bitfields

In cases where a structured binding declaration is made to a struct with
bitfields:

struct A {
  unsigned int x : 16;
  unsigned int y : 16;
} g;

auto [a, b] = g; // structured binding declaration

Clang assigns the 'unsigned int' DWARF base type to 'a' and 'b' because
this is their deduced C++ type in the structured binding declaration.

However, their actual type in memory is 'unsigned short' as they have 16
bits allocated for each.

This is a problem for debug information consumers: if the debug
information for 'a' has the 'unsigned int' base type, a debugger will
assume it has 4 bytes, whereas it actually has a length of 2, resulting
in a read (or write) past its length.

This patch mimics GCC's behaviour: in case of structured bindings to
bitfields, the binding declaration's DWARF base type is of the target's
integer type with the same bitwidth as the bitfield.

If no suitable integer type is found in the target, no debug information
is emitted anymore in order to prevent wrong debug output.

Reviewed By: tmatheson

Differential Revision: https://reviews.llvm.org/D157479
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@vhscampos
vhscampos committed Aug 16, 2023
1 parent 51eaee3 commit d77cba6
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Showing 3 changed files with 329 additions and 2 deletions.
43 changes: 41 additions & 2 deletions clang/lib/CodeGen/CGDebugInfo.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4744,6 +4744,40 @@ 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 @@ -4758,8 +4792,7 @@ llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const BindingDecl *BD,
if (isa<DeclRefExpr>(BD->getBinding()))
return nullptr;

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

// If there is no debug info for this type then do not emit debug info
// for this variable.
Expand All @@ -4785,6 +4818,7 @@ 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 @@ -4800,6 +4834,11 @@ llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const BindingDecl *BD,
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;

Expr.push_back(llvm::dwarf::DW_OP_plus_uconst);
Expr.push_back(
CGM.getContext().toCharUnitsFromBits(fieldOffset).getQuantity());
Expand Down
3 changes: 3 additions & 0 deletions clang/lib/CodeGen/CGDebugInfo.h
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Original file line number Diff line number Diff line change
Expand Up @@ -337,6 +337,9 @@ 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
285 changes: 285 additions & 0 deletions clang/test/CodeGenCXX/debug-info-structured-binding-bitfield.cpp
View file
Original file line number Diff line number Diff line change
@@ -0,0 +1,285 @@
// RUN: %clang_cc1 -emit-llvm -debug-info-kind=standalone -triple aarch64-arm-none-eabi %s -o - | FileCheck %s

struct S0 {
unsigned int x : 16;
unsigned int y : 16;
};

// CHECK-LABEL: define dso_local void @_Z3fS0v
// CHECK: alloca %struct.S0, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S0, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S0_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S0_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 2))
//
void fS0() {
S0 s0;
auto [a, b] = s0;
}

struct S1 {
volatile unsigned int x : 16;
volatile unsigned int y : 16;
};

// CHECK-LABEL: define dso_local void @_Z3fS1v
// CHECK: alloca %struct.S1, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S1, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S1_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S1_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 2))
//
void fS1() {
S1 s1;
auto [a, b] = s1;
}

struct S2 {
unsigned int x : 8;
unsigned int y : 8;
};

// CHECK-LABEL: define dso_local void @_Z3fS2v
// CHECK: alloca %struct.S2, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S2, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S2_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S2_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 1))
//
void fS2() {
S2 s2;
auto [a, b] = s2;
}

struct S3 {
volatile unsigned int x : 8;
volatile unsigned int y : 8;
};

// CHECK-LABEL: define dso_local void @_Z3fS3v
// CHECK: alloca %struct.S3, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S3, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S3_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S3_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 1))
//
void fS3() {
S3 s3;
auto [a, b] = s3;
}

struct S4 {
unsigned int x : 8;
unsigned int y : 16;
};

// CHECK-LABEL: define dso_local void @_Z3fS4v
// CHECK: alloca %struct.S4, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S4, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S4_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S4_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 1))
//
void fS4() {
S4 s4;
auto [a, b] = s4;
}

struct S5 {
volatile unsigned int x : 8;
volatile unsigned int y : 16;
};

// CHECK-LABEL: define dso_local void @_Z3fS5v
// CHECK: alloca %struct.S5, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S5, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S5_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S5_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 1))
//
void fS5() {
S5 s5;
auto [a, b] = s5;
}

struct S6 {
unsigned int x : 16;
unsigned int y : 8;
};

// CHECK-LABEL: define dso_local void @_Z3fS6v
// CHECK: alloca %struct.S6, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S6, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S6_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S6_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 2))
//
void fS6() {
S6 s6;
auto [a, b] = s6;
}

struct S7 {
volatile unsigned int x : 16;
volatile unsigned int y : 8;
};

// CHECK-LABEL: define dso_local void @_Z3fS7v
// CHECK: alloca %struct.S7, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S7, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S7_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S7_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 2))
//
void fS7() {
S7 s7;
auto [a, b] = s7;
}

struct S8 {
unsigned int x : 16;
volatile unsigned int y : 16;
};

// CHECK-LABEL: define dso_local void @_Z3fS8v
// CHECK: alloca %struct.S8, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S8, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S8_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S8_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 2))
//
void fS8() {
S8 s8;
auto [a, b] = s8;
}

struct S9 {
unsigned int x : 16;
unsigned int y : 32;
};

// CHECK-LABEL: define dso_local void @_Z3fS9v
// CHECK: alloca %struct.S9, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S9, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S9_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S9_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 4))
//
void fS9() {
S9 s9;
auto [a, b] = s9;
}

struct S10 {
const unsigned int x : 8;
const volatile unsigned int y : 8;

// CHECK-LABEL: define dso_local void @_Z4fS10v
// CHECK: alloca %struct.S10, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S10, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S10_A:![0-9]+]], metadata !DIExpression())
// CHECK-NEXT: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S10_B:![0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 1))
//
S10() : x(0), y(0) {}
};

void fS10() {
S10 s10;
auto [a, b] = s10;
}

// It's currently not possible to produce complete debug information for the following cases.
// Confirm that no wrong debug info is output.
// Once this is implemented, these tests should be amended.
struct S11 {
unsigned int x : 15;
unsigned int y : 16;
};

// CHECK-LABEL: define dso_local void @_Z4fS11v
// CHECK: alloca %struct.S11, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S11, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]]
// CHECK-NOT: call void @llvm.dbg.declare(metadata ptr [[TMP0]]
//
void fS11() {
S11 s11;
auto [a, b] = s11;
}

struct S12 {
unsigned int x : 16;
unsigned int y : 17;
};

// CHECK-LABEL: define dso_local void @_Z4fS12v
// CHECK: alloca %struct.S12, align 4
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S12, align 4
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S12_A:![0-9]+]], metadata !DIExpression())
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]]
// CHECK-NOT: call void @llvm.dbg.declare(metadata ptr [[TMP0]]
//
void fS12() {
S12 s12;
auto [a, b] = s12;
}

struct __attribute__((packed)) S13 {
unsigned int x : 15;
unsigned int y : 16;
};

// CHECK-LABEL: define dso_local void @_Z4fS13v
// CHECK: alloca %struct.S13, align 1
// CHECK-NEXT: [[TMP0:%.*]] = alloca %struct.S13, align 1
// CHECK: call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata {{.*}}, metadata !DIExpression())
// CHECK-NOT: call void @llvm.dbg.declare(metadata ptr [[TMP0]]
//
void fS13() {
S13 s13;
auto [a, b] = s13;
}

// CHECK: [[UINT_TY:![0-9]+]] = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
// CHECK: [[S0_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[USHORT_TY:![0-9]+]])
// CHECK: [[USHORT_TY]] = !DIBasicType(name: "unsigned short", size: 16, encoding: DW_ATE_unsigned)
// CHECK: [[S0_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[USHORT_TY]])

// CHECK: [[VOLATILE_UINT_TY:![0-9]+]] = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: [[UINT_TY]])
// CHECK: [[S1_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[VOLATILE_USHORT_TY:![0-9]+]])
// CHECK: [[VOLATILE_USHORT_TY]] = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: [[USHORT_TY]])
// CHECK: [[S1_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[VOLATILE_USHORT_TY]])

// CHECK: [[S2_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[UCHAR_TY:![0-9]+]])
// CHECK: [[UCHAR_TY]] = !DIBasicType(name: "unsigned char", size: 8, encoding: DW_ATE_unsigned_char)
// CHECK: [[S2_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[UCHAR_TY]])

// CHECK: [[S3_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[VOLATILE_UCHAR_TY:![0-9]+]])
// CHECK: [[VOLATILE_UCHAR_TY]] = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: [[UCHAR_TY]])
// CHECK: [[S3_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[VOLATILE_UCHAR_TY]])

// CHECK: [[S4_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[UCHAR_TY]])
// CHECK: [[S4_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[USHORT_TY]])

// CHECK: [[S5_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[VOLATILE_UCHAR_TY]])
// CHECK: [[S5_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[VOLATILE_USHORT_TY]])

// CHECK: [[S6_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[USHORT_TY]])
// CHECK: [[S6_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[UCHAR_TY]])

// CHECK: [[S7_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[VOLATILE_USHORT_TY]])
// CHECK: [[S7_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[VOLATILE_UCHAR_TY]])

// CHECK: [[S8_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[USHORT_TY]])
// CHECK: [[S8_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[VOLATILE_USHORT_TY]])

// CHECK: [[S9_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[USHORT_TY]])
// CHECK: [[S9_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[UINT_TY]])

// CHECK: [[CONST_UINT_TY:![0-9]+]] = !DIDerivedType(tag: DW_TAG_const_type, baseType: [[UINT_TY]])
// CHECK: [[S10_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[CONST_UCHAR_TY:![0-9]+]])
// CHECK: [[CONST_UCHAR_TY]] = !DIDerivedType(tag: DW_TAG_const_type, baseType: [[UCHAR_TY]])
// CHECK: [[S10_B]] = !DILocalVariable(name: "b", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[CONST_VOLATILE_UCHAR_TY:![0-9]+]])
// CHECK: [[CONST_VOLATILE_UCHAR_TY]] = !DIDerivedType(tag: DW_TAG_const_type, baseType: [[VOLATILE_UCHAR_TY]])

// S11
// CHECK-NOT: !DILocalVariable(name: "a"
// CHECK-NOT: !DILocalVariable(name: "b"

// S12
// CHECK: [[S12_A]] = !DILocalVariable(name: "a", scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: [[USHORT_TY]])
// CHECK-NOT: !DILocalVariable(name: "b"

// S13
// CHECK-NOT: !DILocalVariable(name: "a"
// CHECK-NOT: !DILocalVariable(name: "b"

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