hwasan: add tag_offset DWARF attribute to optimized debug info

[eugenis]

Summary

Support alloca-referencing dbg.value in hwasan instrumentation.
Update AsmPrinter to emit DW_AT_LLVM_tag_offset when location is in
loclist format.

[aprantl]

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h

121

///

llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

1049

DIExpression::prependOpcodes()?

[eugenis]

.

[eugenis]

.

[eugenis]

PTAL

[eugenis]

ping

[pcc]

LGTM

[dblaikie]

llvm/test/CodeGen/AArch64/dbg-value-tag-offset.ll

6–16

Usually DWARF is tested with dwarfdump, not raw assembly - is there a reason this isn't tested that way?

[eugenis]

llvm/test/CodeGen/AArch64/dbg-value-tag-offset.ll

6–16

I've cargo-culted the dbg-declare-tag-offset.ll test by @pcc .
This should not be too hard to switch to llvm-dwarfdump.

[eugenis]

https://reviews.llvm.org/D72023

llvm/lib/CodeGen/AsmPrinter/DebugLocStream.h

 
 /// Builder for DebugLocStream lists.
 class DebugLocStream::ListBuilder {
   DebugLocStream &Locs;
   AsmPrinter &Asm;
   DbgVariable &V;
   const MachineInstr &MI;
   size_t ListIndex;
+  Optional<uint8_t> TagOffset;
 
 public:
   ListBuilder(DebugLocStream &Locs, DwarfCompileUnit &CU, AsmPrinter &Asm,
               DbgVariable &V, const MachineInstr &MI)
-      : Locs(Locs), Asm(Asm), V(V), MI(MI), ListIndex(Locs.startList(&CU)) {}
+      : Locs(Locs), Asm(Asm), V(V), MI(MI), ListIndex(Locs.startList(&CU)),
+        TagOffset(None) {}
+
+  void setTagOffset(uint8_t TO) {
+    TagOffset = TO;
+  }
 
   /// Finalize the list.
   ///
   /// If the list is empty, delete it.  Otherwise, finalize it by creating a
   /// temp symbol in \a Asm and setting up the \a DbgVariable.
   ~ListBuilder();
 
   DebugLocStream &getLocs() { return Locs; }

llvm/lib/CodeGen/AsmPrinter/DebugLocStream.cpp

assert(Lists.back().EntryOffset <= Entries.size() &&
          "Popped off more entries than are in the list");
 }
 
 DebugLocStream::ListBuilder::~ListBuilder() {
   if (!Locs.finalizeList(Asm))
     return;
   V.initializeDbgValue(&MI);
   V.setDebugLocListIndex(ListIndex);
+  if (TagOffset)
+    V.setDebugLocListTagOffset(*TagOffset);
 }

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

if (Abstract) {
     return VariableDie;
   }
 
   // Add variable address.
 
   unsigned Offset = DV.getDebugLocListIndex();
   if (Offset != ~0U) {
     addLocationList(*VariableDie, dwarf::DW_AT_location, Offset);
+    auto TagOffset = DV.getDebugLocListTagOffset();
+    if (TagOffset)
+      addUInt(*VariableDie, dwarf::DW_AT_LLVM_tag_offset, dwarf::DW_FORM_data1,
+              *TagOffset);
     return VariableDie;
   }
 
   // Check if variable has a single location description.
   if (auto *DVal = DV.getValueLoc()) {
     if (DVal->isLocation())
       addVariableAddress(DV, *VariableDie, DVal->getLoc());
     else if (DVal->isInt()) {
       auto *Expr = DV.getSingleExpression();
       if (Expr && Expr->getNumElements()) {
         DIELoc *Loc = new (DIEValueAllocator) DIELoc;
         DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
         // If there is an expression, emit raw unsigned bytes.
         DwarfExpr.addFragmentOffset(Expr);
         DwarfExpr.addUnsignedConstant(DVal->getInt());
         DwarfExpr.addExpression(Expr);
         addBlock(*VariableDie, dwarf::DW_AT_location, DwarfExpr.finalize());
+        if (DwarfExpr.TagOffset)
+          addUInt(*VariableDie, dwarf::DW_AT_LLVM_tag_offset,
+                  dwarf::DW_FORM_data1, *DwarfExpr.TagOffset);
+
       } else
         addConstantValue(*VariableDie, DVal->getInt(), DV.getType());
     } else if (DVal->isConstantFP()) {
       addConstantFPValue(*VariableDie, DVal->getConstantFP());
     } else if (DVal->isConstantInt()) {
       addConstantValue(*VariableDie, DVal->getConstantInt(), DV.getType());
     }
     return VariableDie;
void DwarfCompileUnit::addAddress(DIE &Die, dwarf::Attribute Attribute,
   DIExpressionCursor Cursor({});
   const TargetRegisterInfo &TRI = *Asm->MF->getSubtarget().getRegisterInfo();
   if (!DwarfExpr.addMachineRegExpression(TRI, Cursor, Location.getReg()))
     return;
   DwarfExpr.addExpression(std::move(Cursor));
 
   // Now attach the location information to the DIE.
   addBlock(Die, Attribute, DwarfExpr.finalize());
+
+  if (DwarfExpr.TagOffset)
+    addUInt(Die, dwarf::DW_AT_LLVM_tag_offset, dwarf::DW_FORM_data1,
+            *DwarfExpr.TagOffset);
 }
 
 /// Start with the address based on the location provided, and generate the
 /// DWARF information necessary to find the actual variable given the extra
 /// address information encoded in the DbgVariable, starting from the starting
 /// location.  Add the DWARF information to the die.
 void DwarfCompileUnit::addComplexAddress(const DbgVariable &DV, DIE &Die,
                                          dwarf::Attribute Attribute,
void DwarfCompileUnit::addComplexAddress(const DbgVariable &DV, DIE &Die,
 
   const TargetRegisterInfo &TRI = *Asm->MF->getSubtarget().getRegisterInfo();
   if (!DwarfExpr.addMachineRegExpression(TRI, Cursor, Location.getReg()))
     return;
   DwarfExpr.addExpression(std::move(Cursor));
 
   // Now attach the location information to the DIE.
   addBlock(Die, Attribute, DwarfExpr.finalize());
+
+  if (DwarfExpr.TagOffset)
+    addUInt(Die, dwarf::DW_AT_LLVM_tag_offset, dwarf::DW_FORM_data1,
+            *DwarfExpr.TagOffset);
 }
 
 /// Add a Dwarf loclistptr attribute data and value.
 void DwarfCompileUnit::addLocationList(DIE &Die, dwarf::Attribute Attribute,
                                        unsigned Index) {
   dwarf::Form Form = dwarf::DW_FORM_data4;
   if (DD->getDwarfVersion() == 4)
     Form =dwarf::DW_FORM_sec_offset;

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h

 /// Variables can be created from \c DBG_VALUE instructions.  Those whose
 /// location changes over time use \a DebugLocListIndex, while those with a
 /// single location use \a ValueLoc and (optionally) a single entry of \a Expr.
 ///
 /// Variables that have been optimized out use none of these fields.
 class DbgVariable : public DbgEntity {
   /// Offset in DebugLocs.
   unsigned DebugLocListIndex = ~0u;
+  // DW_OP_LLVM_tag_offset value from DebugLocs.
+  Optional<uint8_t> DebugLocListTagOffset;
+
   /// Single value location description.
   std::unique_ptr<DbgValueLoc> ValueLoc = nullptr;
 
   struct FrameIndexExpr {
     int FI;
     const DIExpression *Expr;
   };
   mutable SmallVector<FrameIndexExpr, 1>
public:
 
   const DIExpression *getSingleExpression() const {
     assert(ValueLoc.get() && FrameIndexExprs.size() <= 1);
     return FrameIndexExprs.size() ? FrameIndexExprs[0].Expr : nullptr;
   }
 
   void setDebugLocListIndex(unsigned O) { DebugLocListIndex = O; }
   unsigned getDebugLocListIndex() const { return DebugLocListIndex; }
+  void setDebugLocListTagOffset(uint8_t O) { DebugLocListTagOffset = O; }
+  Optional<uint8_t> getDebugLocListTagOffset() const { return DebugLocListTagOffset; }
   StringRef getName() const { return getVariable()->getName(); }
   const DbgValueLoc *getValueLoc() const { return ValueLoc.get(); }
   /// Get the FI entries, sorted by fragment offset.
   ArrayRef<FrameIndexExpr> getFrameIndexExprs() const;
   bool hasFrameIndexExprs() const { return !FrameIndexExprs.empty(); }
   void addMMIEntry(const DbgVariable &V);
 
   // Translate tag to proper Dwarf tag.

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

if (Value.isFragment()) {
     for (auto Fragment : Values)
       DwarfDebug::emitDebugLocValue(AP, BT, Fragment, DwarfExpr);
 
   } else {
     assert(Values.size() == 1 && "only fragments may have >1 value");
     DwarfDebug::emitDebugLocValue(AP, BT, Value, DwarfExpr);
   }
   DwarfExpr.finalize();
+  if (DwarfExpr.TagOffset)
+    List.setTagOffset(*DwarfExpr.TagOffset);
 }
 
 void DwarfDebug::emitDebugLocEntryLocation(const DebugLocStream::Entry &Entry,
                                            const DwarfCompileUnit *CU) {
   // Emit the size.
   Asm->OutStreamer->AddComment("Loc expr size");
   if (getDwarfVersion() >= 5)
     Asm->EmitULEB128(DebugLocs.getBytes(Entry).size());

llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

Value *isInterestingMemoryAccess(Instruction *I, bool *IsWrite,
                                    Value **MaybeMask);
 
   bool isInterestingAlloca(const AllocaInst &AI);
   bool tagAlloca(IRBuilder<> &IRB, AllocaInst *AI, Value *Tag, size_t Size);
   Value *tagPointer(IRBuilder<> &IRB, Type *Ty, Value *PtrLong, Value *Tag);
   Value *untagPointer(IRBuilder<> &IRB, Value *PtrLong);
   bool instrumentStack(
       SmallVectorImpl<AllocaInst *> &Allocas,
-      DenseMap<AllocaInst *, std::vector<DbgDeclareInst *>> &AllocaDeclareMap,
+      DenseMap<AllocaInst *, std::vector<DbgVariableIntrinsic *>> &AllocaDbgMap,
       SmallVectorImpl<Instruction *> &RetVec, Value *StackTag);
   Value *readRegister(IRBuilder<> &IRB, StringRef Name);
   bool instrumentLandingPads(SmallVectorImpl<Instruction *> &RetVec);
   Value *getNextTagWithCall(IRBuilder<> &IRB);
   Value *getStackBaseTag(IRBuilder<> &IRB);
   Value *getAllocaTag(IRBuilder<> &IRB, Value *StackTag, AllocaInst *AI,
                      unsigned AllocaNo);
   Value *getUARTag(IRBuilder<> &IRB, Value *StackTag);
IRB.CreateCall(
         {readRegister(IRB, (TargetTriple.getArch() == Triple::x86_64) ? "rsp"
                                                                       : "sp")});
   }
   return true;
 }
 
 bool HWAddressSanitizer::instrumentStack(
     SmallVectorImpl<AllocaInst *> &Allocas,
-    DenseMap<AllocaInst *, std::vector<DbgDeclareInst *>> &AllocaDeclareMap,
+    DenseMap<AllocaInst *, std::vector<DbgVariableIntrinsic *>> &AllocaDbgMap,
     SmallVectorImpl<Instruction *> &RetVec, Value *StackTag) {
   // Ideally, we want to calculate tagged stack base pointer, and rewrite all
   // alloca addresses using that. Unfortunately, offsets are not known yet
   // (unless we use ASan-style mega-alloca). Instead we keep the base tag in a
   // temp, shift-OR it into each alloca address and xor with the retag mask.
   // This generates one extra instruction per alloca use.
   for (unsigned N = 0; N < Allocas.size(); ++N) {
     auto *AI = Allocas[N];
     IRBuilder<> IRB(AI->getNextNode());
 
     // Replace uses of the alloca with tagged address.
     Value *Tag = getAllocaTag(IRB, StackTag, AI, N);
     Value *AILong = IRB.CreatePointerCast(AI, IntptrTy);
     Value *Replacement = tagPointer(IRB, AI->getType(), AILong, Tag);
     std::string Name =
         AI->hasName() ? AI->getName().str() : "alloca." + itostr(N);
     Replacement->setName(Name + ".hwasan");
 
     AI->replaceUsesWithIf(Replacement,
                           [AILong](Use &U) { return U.getUser() != AILong; });
 
-    for (auto *DDI : AllocaDeclareMap.lookup(AI)) {
+    for (auto *DDI : AllocaDbgMap.lookup(AI)) {
+      // Prepend "tag_offset, N" to the dwarf expression.
+      // Tag offset logically applies to the alloca pointer, and it makes sense
+      // to put it at the beginning of the expression.
       DIExpression *OldExpr = DDI->getExpression();
-      DIExpression *NewExpr = DIExpression::append(
-          OldExpr, {dwarf::DW_OP_LLVM_tag_offset, RetagMask(N)});
+      SmallVector<uint64_t, 8> NewOps = {dwarf::DW_OP_LLVM_tag_offset,
+                                         RetagMask(N)};
+      NewOps.append(OldExpr->elements_begin(), OldExpr->elements_end());
+      DIExpression *NewExpr = DIExpression::get(*C, NewOps);
       DDI->setArgOperand(2, MetadataAsValue::get(*C, NewExpr));
     }
 
     size_t Size = getAllocaSizeInBytes(*AI);
     tagAlloca(IRB, AI, Tag, Size);
 
     for (auto RI : RetVec) {
       IRB.SetInsertPoint(RI);
if (!F.hasFnAttribute(Attribute::SanitizeHWAddress))
     return false;
 
   LLVM_DEBUG(dbgs() << "Function: " << F.getName() << "\n");
 
   SmallVector<Instruction*, 16> ToInstrument;
   SmallVector<AllocaInst*, 8> AllocasToInstrument;
   SmallVector<Instruction*, 8> RetVec;
   SmallVector<Instruction*, 8> LandingPadVec;
-  DenseMap<AllocaInst *, std::vector<DbgDeclareInst *>> AllocaDeclareMap;
+  DenseMap<AllocaInst *, std::vector<DbgVariableIntrinsic *>> AllocaDbgMap;
   for (auto &BB : F) {
     for (auto &Inst : BB) {
       if (ClInstrumentStack)
         if (AllocaInst *AI = dyn_cast<AllocaInst>(&Inst)) {
           if (isInterestingAlloca(*AI))
             AllocasToInstrument.push_back(AI);
           continue;
         }
 
       if (isa<ReturnInst>(Inst) || isa<ResumeInst>(Inst) ||
           isa<CleanupReturnInst>(Inst))
         RetVec.push_back(&Inst);
 
-      if (auto *DDI = dyn_cast<DbgDeclareInst>(&Inst))
-        if (auto *Alloca = dyn_cast_or_null<AllocaInst>(DDI->getAddress()))
-          AllocaDeclareMap[Alloca].push_back(DDI);
+      if (auto *DDI = dyn_cast<DbgVariableIntrinsic>(&Inst))
+        if (auto *Alloca =
+                dyn_cast_or_null<AllocaInst>(DDI->getVariableLocation()))
+          AllocaDbgMap[Alloca].push_back(DDI);
 
       if (InstrumentLandingPads && isa<LandingPadInst>(Inst))
         LandingPadVec.push_back(&Inst);
 
       Value *MaybeMask = nullptr;
       bool IsWrite;
       unsigned Alignment;
       uint64_t TypeSize;
bool HWAddressSanitizer::sanitizeFunction(Function &F) {
   emitPrologue(EntryIRB,
                /*WithFrameRecord*/ ClRecordStackHistory &&
                    !AllocasToInstrument.empty());
 
   bool Changed = false;
   if (!AllocasToInstrument.empty()) {
     Value *StackTag =
         ClGenerateTagsWithCalls ? nullptr : getStackBaseTag(EntryIRB);
-    Changed |= instrumentStack(AllocasToInstrument, AllocaDeclareMap, RetVec,
+    Changed |= instrumentStack(AllocasToInstrument, AllocaDbgMap, RetVec,
                                StackTag);
   }
 
   // Pad and align each of the allocas that we instrumented to stop small
   // uninteresting allocas from hiding in instrumented alloca's padding and so
   // that we have enough space to store real tags for short granules.
   DenseMap<AllocaInst *, AllocaInst *> AllocaToPaddedAllocaMap;
   for (AllocaInst *AI : AllocasToInstrument) {

llvm/test/CodeGen/AArch64/dbg-value-tag-offset.ll

+; RUN: llc -o - %s | FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64-unknown-linux-android24"
+
+; CHECK: .Linfo_string5:
+; CHECK-NEXT: .asciz "y"
+; CHECK: .Linfo_string7:
+; CHECK-NEXT: .asciz "x"
+
+; CHECK:      .byte   128                     // DW_AT_LLVM_tag_offset
+; CHECK-NEXT: .word   .Linfo_string5          // DW_AT_name
+; CHECK:      .byte   0                       // DW_AT_LLVM_tag_offset
+; CHECK-NEXT: .word   .Linfo_string7          // DW_AT_name
+
+define dso_local void @f() !dbg !14 {
+  %1 = alloca i32, align 4
+  %2 = alloca i32, align 4
+  %3 = bitcast i32* %1 to i8*, !dbg !21
+  %4 = bitcast i32* %2 to i8*, !dbg !21
+  call void @llvm.dbg.value(metadata i32 1, metadata !20, metadata !DIExpression()), !dbg !22
+  store i32 1, i32* %2, align 4, !dbg !23, !tbaa !24
+  call void @llvm.dbg.value(metadata i32* %1, metadata !18, metadata !DIExpression(DW_OP_LLVM_tag_offset, 0, DW_OP_deref)), !dbg !22
+  call void @use(i8* nonnull %3), !dbg !28
+  call void @llvm.dbg.value(metadata i32* %2, metadata !20, metadata !DIExpression(DW_OP_LLVM_tag_offset, 128, DW_OP_deref)), !dbg !22
+  call void @use(i8* nonnull %4), !dbg !29
+  ret void, !dbg !30
+}
+
+declare !dbg !5 void @use(i8*)
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!8, !9, !10, !11, !12}
+!llvm.ident = !{!13}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 10.0.0 ([e-mail]:llvm/llvm-project.git 5560dd08b99a0e8b0c55116376624e4f967caec5)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+!1 = !DIFile(filename: "dbg.cc", directory: "/tmp")
+!2 = !{}
+!3 = !{!4, !5}
+!4 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+!5 = !DISubprogram(name: "use", scope: !1, file: !1, line: 2, type: !6, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+!6 = !DISubroutineType(types: !7)
+!7 = !{null, !4}
+!8 = !{i32 7, !"Dwarf Version", i32 4}
+!9 = !{i32 2, !"Debug Info Version", i32 3}
+!10 = !{i32 1, !"wchar_size", i32 4}
+!11 = !{i32 7, !"PIC Level", i32 2}
+!12 = !{i32 7, !"PIE Level", i32 2}
+!13 = !{!"clang version 10.0.0 ([e-mail]:llvm/llvm-project.git 5560dd08b99a0e8b0c55116376624e4f967caec5)"}
+!14 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 4, type: !15, scopeLine: 4, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !17)
+!15 = !DISubroutineType(types: !16)
+!16 = !{null}
+!17 = !{!18, !20}
+!18 = !DILocalVariable(name: "x", scope: !14, file: !1, line: 5, type: !19)
+!19 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!20 = !DILocalVariable(name: "y", scope: !14, file: !1, line: 5, type: !19)
+!21 = !DILocation(line: 5, column: 3, scope: !14)
+!22 = !DILocation(line: 0, scope: !14)
+!23 = !DILocation(line: 5, column: 10, scope: !14)
+!24 = !{!25, !25, i64 0}
+!25 = !{!"int", !26, i64 0}
+!26 = !{!"omnipotent char", !27, i64 0}
+!27 = !{!"Simple C++ TBAA"}
+!28 = !DILocation(line: 6, column: 3, scope: !14)
+!29 = !DILocation(line: 7, column: 3, scope: !14)
+!30 = !DILocation(line: 8, column: 1, scope: !14)

llvm/test/Instrumentation/HWAddressSanitizer/dbg-value-tag-offset.ll

+; RUN: opt -hwasan -S -o - %s | FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64-unknown-linux-android24"
+
+define dso_local void @f() sanitize_hwaddress !dbg !14 {
+  %1 = alloca i32, align 4
+  %2 = alloca i32, align 4
+  %3 = bitcast i32* %1 to i8*, !dbg !21
+  %4 = bitcast i32* %2 to i8*, !dbg !21
+; CHECK: call void @llvm.dbg.value(metadata i32 1, {{.*}}, metadata !DIExpression())
+  call void @llvm.dbg.value(metadata i32 1, metadata !20, metadata !DIExpression()), !dbg !22
+  store i32 1, i32* %2, align 4, !dbg !23, !tbaa !24
+; CHECK: call void @llvm.dbg.value(metadata i32* {{.*}}, metadata !DIExpression(DW_OP_LLVM_tag_offset, 0, DW_OP_deref))
+  call void @llvm.dbg.value(metadata i32* %1, metadata !18, metadata !DIExpression(DW_OP_deref)), !dbg !22
+  call void @use(i8* nonnull %3), !dbg !28
+; CHECK: call void @llvm.dbg.value(metadata i32* {{.*}}, metadata !DIExpression(DW_OP_LLVM_tag_offset, 128, DW_OP_deref))
+  call void @llvm.dbg.value(metadata i32* %2, metadata !20, metadata !DIExpression(DW_OP_deref)), !dbg !22
+  call void @use(i8* nonnull %4), !dbg !29
+  ret void, !dbg !30
+}
+
+declare !dbg !5 void @use(i8*)
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!8, !9, !10, !11, !12}
+!llvm.ident = !{!13}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 10.0.0 ([e-mail]:llvm/llvm-project.git 5560dd08b99a0e8b0c55116376624e4f967caec5)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+!1 = !DIFile(filename: "dbg.cc", directory: "/tmp")
+!2 = !{}
+!3 = !{!4, !5}
+!4 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+!5 = !DISubprogram(name: "use", scope: !1, file: !1, line: 2, type: !6, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+!6 = !DISubroutineType(types: !7)
+!7 = !{null, !4}
+!8 = !{i32 7, !"Dwarf Version", i32 4}
+!9 = !{i32 2, !"Debug Info Version", i32 3}
+!10 = !{i32 1, !"wchar_size", i32 4}
+!11 = !{i32 7, !"PIC Level", i32 2}
+!12 = !{i32 7, !"PIE Level", i32 2}
+!13 = !{!"clang version 10.0.0 ([e-mail]:llvm/llvm-project.git 5560dd08b99a0e8b0c55116376624e4f967caec5)"}
+!14 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 4, type: !15, scopeLine: 4, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !17)
+!15 = !DISubroutineType(types: !16)
+!16 = !{null}
+!17 = !{!18, !20}
+!18 = !DILocalVariable(name: "x", scope: !14, file: !1, line: 5, type: !19)
+!19 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!20 = !DILocalVariable(name: "y", scope: !14, file: !1, line: 5, type: !19)
+!21 = !DILocation(line: 5, column: 3, scope: !14)
+!22 = !DILocation(line: 0, scope: !14)
+!23 = !DILocation(line: 5, column: 10, scope: !14)
+!24 = !{!25, !25, i64 0}
+!25 = !{!"int", !26, i64 0}
+!26 = !{!"omnipotent char", !27, i64 0}
+!27 = !{!"Simple C++ TBAA"}
+!28 = !DILocation(line: 6, column: 3, scope: !14)
+!29 = !DILocation(line: 7, column: 3, scope: !14)
+!30 = !DILocation(line: 8, column: 1, scope: !14)