Debug Info Support for Basic Block Sections

[tmsriram]

Summary

This patch adds basic debug info support with basic block sections supported in D68063 and D73674.

The original author of this patch is @amharc and I am presenting this for review on his behalf.

This patch uses ranges for debug information when a function contains basic block sections rather than using [lowpc, highpc]. This is also the first in a series of patches for debug info and does not contain the support for linker relaxation. That will be done as a follow up patch.

[tmsriram]

Update patch with missing file (MachineBasicBlock.h) and simplify test.

[tmsriram]

Rebase and add a test for fission.

[tmsriram]

Rebase

[tmsriram]

Ping.

[dblaikie]

This is currently only for "basic block sections", right? No linker relaxation, etc? (so symbol differences within a bb section (even using symbols at the very end of the bb section, after the trailing jump) are valid/knowable at compile-time/don't change during linking)

llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp

215–223

Is there a test case covering this? Rough sense of how much this hurts debug info quality?

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

592–597

Would this fall out naturally/produce the same answer as the loop below? If so, I'd probably let it happen that way rather than special casing it.

598–609

Probably add a comment describing what's happening here (similar to the comment above about the continuous range case)

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

2030–2042

If you remove the &MBB != &MF->front() case, would the function begin/end entry fall out/be produced by the loop? (or is "MBBSectionRanges" only valid if "hasBBSections"? Maybe it'd be handy if it always contained the ranges - just one range when "hasBBSections" is false?)

llvm/test/DebugInfo/X86/basicblock-sections_1.ll

14–17

This might be a case where testing the assembly would be appropriate - to check which symbols and symbolic expressions are used for the ranges/high/low rather than only that is "some range".

[tmsriram]

Rebase and address reviewer comments which are code refactoring and enhancing the test case.

llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp

215–223

I am still working on getting a test case for this. I will iterate on this shortly.

llvm/test/DebugInfo/X86/basicblock-sections_1.ll

14–17

I have added checks for the assembly. Please let me know if there is something specific you want to check here.

[dblaikie]

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

401–411

This is a bit of a duplicate of the code in DwarfDebug::endFunctionImpl - perhaps it could be refactored into a reusable function in some way?

401–413

Does this code produce the correct behavior when !BBSections? If so, I don't think it's worth the special-case for !BBSections - happy to just let it flow out from this code.

596

Probably "Otherwise, low/high PC can be used."

llvm/test/DebugInfo/X86/basicblock-sections_1.ll

45–46

Probably put this up along with the NO-SECTIONS dwarfdump testing.

Also - probably best to test the .debug_info section rather than the .debug_abbrev section. You can add -v to dump which will print forms and sections:

no sections:

DW_AT_low_pc [DW_FORM_addr] (0x0000000000000000 ".text")
DW_AT_high_pc [DW_FORM_data4] ({{.*}})

basic block sections:

DW_AT_low_pc [DW_FORM_addr] (0x0000000000000000)
DW_AT_ranegs [DW_FORM_sec_offset] (
                 [0x0000000000000000, {{.*}}) ".text._Z2f1v"
                 [0x0000000000000000, {{.*}}) ".text._Z2f2v")

or something like that (I mean that sample was from function sections, but bb sections should work similarly - easier with unique section names to identify which ones are there)

[tmsriram]

Address reviewer comments :

+ Refactor code
+ Fix test to use --debug-info

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

401–411

It is really small now. deduping complicates it as one is a simple list and the other is DwarfCompileUnit::addRange.

[dblaikie]

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

597–608

Hmm, the existence of this code makes me think that this means LLVM debug info emission depends on block order. If some optimization did interesting things to block order it could break/change the semantics of the DWARF emitted.

That's perhaps a big enough bug that it's out of scope to deal with here (@aprantl @JDevlieghere @probinson - just FYI to keep in mind), but hopefully a general solution to this problem would remove the need for this code here. (& then no need for MBBSectionRanges to be a map, probably).

Maybe include a FIXME above this code to explain that?

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

2034–2035

Could we iterate MBBSectionRanges (it looks like it's built per-function?) instead of iterating BBs and looking up MBBSectionRanges? Looks like /maybe/ this code could be:

for (const auto &R : Asm->MBBSectionRanges)
  TheCU.addRange(R.second.BeginLabel, R.second.EndLabel);

(similarly for the code in updateSubprogramScopeDIE)

[tmsriram]

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

2034–2035

IndexedMap does not support begin() end() iterators, so this won't work right? This is a good idea but I might have to find a different Map data structure that is viable. A DenseMap variant looks good as section IDs can be mapped to a small dense set of integers, but DenseMap does not support this either?

[dblaikie]

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

2034–2035

Ah, I see - yeah, I think it'd probably be fine to just use a DenseMap<MCSection*, LabelRangeThing>, but I can see the nice-ness of the IndexedMap.

Are the section IDs unique just to the BB sections of one function? Otherwise it seems inefficient to have a map that's as big as all the sections in the output object file to be able to do indexed lookup into, compared to a denser map data structure - but perhaps it's still a small enough number that flat/indexed lookup is better.

In any case, it probably wouldn't be too hard to add begin/end filter_iterators to IndexedMap.

DenseMap should support iteration (implemented in DenseMapBase) - but has the problem of unreliable ordering (even for non-pointer keys, like ints - we shouldn't depend on the ordering of a hash data structure), so that'd make the output unstable, which isn't any good.

So maybe adding filtering iteration for IndexedMap is the right way to go - though I still wouldn't'd mind knowing just how big this IndexedMap gets - hmmm, I guess from the way it's built "getNumBlockIDs" means it is function-locally-unique, not whole-output-file-unique, which means it shouldn't be just as big as it needs to be. Sounds good.

[tmsriram]

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

2034–2035

Yes, the section IDs correspond to the BB section of one function. Worst case, each BB goes into one section and gets a entry in the map. I do not have a average case number with section clusters and inter-procedural layout, but is probably like one-third the number of basic blocks if I have to hazard a guess.

I can look at adding begin/end iterators to Indexed Map. It looks like it is using a vector underneath which is pre-allocated in size. If I have to scan the vector fully then it is probably not more efficient than what we have right now as it is still linear in the number of basic blocks and not sections, but I can take a closer look.

[tmsriram]

Use MapVector for MBBSectionRanges instead of IndexedMap.

MapVector guarantees fast lookups and iterations and preserves the insertion order.

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

2034–2035

TLDR; MapVector seems to work great for this use case, lookups and iterations are fast. Deletions are slow but we don' do this.

+ IndexedMap is not what we want. Maybe I just don't get it but it is basically a vector underneath and the mapping of key->integers is left to the user. If it is sparse, iterating becomes an issue as we have to go over non-existent elements. It also requires early resizing. My feeling is IndexedMap was never made to be iterated.
+ MapVector is still off DenseMap and this seems to work perfect here. A plain vector would do if we solve the block order problem which you noted.

[tmsriram]

Remove check for skipping debug info in DebugHandlerBase.cpp as it is not needed.

llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp

215–223

I removed these lines and did a full bootstrap with debuginfo and assertions enabled with basic block sections and see no issues. These lines were added before we got a lot of debug info right and this seems no longer necessary.

[dblaikie]

Looks good - thanks!

llvm/include/llvm/CodeGen/AsmPrinter.h

 // asm writers.  This class primarily handles common functionality used by
 // all asm writers.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CODEGEN_ASMPRINTER_H
 #define LLVM_CODEGEN_ASMPRINTER_H
 
+#include "llvm/ADT/IndexedMap.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/CodeGen/AsmPrinterHandler.h"
 #include "llvm/CodeGen/DwarfStringPoolEntry.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/IR/InlineAsm.h"
public:
   /// at the beginning of each call to SetupMachineFunction().
   MCSymbol *CurrentFnDescSym = nullptr;
 
   /// The symbol used to represent the start of the current function for the
   /// purpose of calculating its size (e.g. using the .size directive). By
   /// default, this is equal to CurrentFnSym.
   MCSymbol *CurrentFnSymForSize = nullptr;
 
+  /// Map a basic block section ID to the begin and end symbols of that section
+  ///  which determine the section's range.
+  struct MBBSectionRange {
+    MCSymbol *BeginLabel, *EndLabel;
+  };
+  IndexedMap<MBBSectionRange, MBBSectionID::ToIndexFunctor> MBBSectionRanges;
+
   /// Map global GOT equivalent MCSymbols to GlobalVariables and keep track of
   /// its number of uses by other globals.
   using GOTEquivUsePair = std::pair<const GlobalVariable *, unsigned>;
   MapVector<const MCSymbol *, GOTEquivUsePair> GlobalGOTEquivs;
 
 private:
   MCSymbol *CurrentFnEnd = nullptr;
   MCSymbol *CurExceptionSym = nullptr;

llvm/include/llvm/CodeGen/AsmPrinterHandler.h

virtual void beginFunclet(const MachineBasicBlock &MBB,
                             MCSymbol *Sym = nullptr) {}
   virtual void endFunclet() {}
 
   /// Process beginning of an instruction.
   virtual void beginInstruction(const MachineInstr *MI) = 0;
 
   /// Process end of an instruction.
   virtual void endInstruction() = 0;
+
+  /// Process beginning of a basic block during basic block sections.
+  virtual void beginBasicBlock(const MachineBasicBlock &MBB) {}
+
+  /// Process end of a basic block during basic block sections.
+  virtual void endBasicBlock(const MachineBasicBlock &MBB) {}
 };
 } // End of namespace llvm
 
 #endif

llvm/include/llvm/CodeGen/DebugHandlerBase.h

protected:
   // AsmPrinterHandler overrides.
 public:
   void beginInstruction(const MachineInstr *MI) override;
   void endInstruction() override;
 
   void beginFunction(const MachineFunction *MF) override;
   void endFunction(const MachineFunction *MF) override;
 
+  void beginBasicBlock(const MachineBasicBlock &MBB) override;
+  void endBasicBlock(const MachineBasicBlock &MBB) override;
+
   /// Return Label preceding the instruction.
   MCSymbol *getLabelBeforeInsn(const MachineInstr *MI);
 
   /// Return Label immediately following the instruction.
   MCSymbol *getLabelAfterInsn(const MachineInstr *MI);
 
   /// If this type is derived from a base type then return base type size.
   static uint64_t getBaseTypeSize(const DIType *Ty);
 };
 
 }
 
 #endif

llvm/include/llvm/CodeGen/MachineBasicBlock.h

struct MBBSectionID {
   const static MBBSectionID ExceptionSectionID;
 
   bool operator==(const MBBSectionID &Other) const {
     return Type == Other.Type && Number == Other.Number;
   }
 
   bool operator!=(const MBBSectionID &Other) const { return !(*this == Other); }
 
+  // This returns a unique index for the section in the range [0, max(Number)+2]
+  struct ToIndexFunctor {
+    using argument_type = MBBSectionID;
+    unsigned operator()(MBBSectionID SectionID) const {
+      return ((unsigned)MBBSectionID::SectionType::Cold) -
+             ((unsigned)SectionID.Type) + SectionID.Number;
+    }
+    static unsigned indexSize(unsigned NumBlockIDs) { return NumBlockIDs + 2; }
+  };
+
 private:
   // This is only used to construct the special cold and exception sections.
   MBBSectionID(SectionType T) : Type(T), Number(0) {}
 };
 
 template <> struct ilist_traits<MachineInstr> {
 private:
   friend class MachineBasicBlock; // Set by the owning MachineBasicBlock.

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

if (MAI->hasDotTypeDotSizeDirective() && MF->hasBBLabels())
       emitELFSizeDirective(MBB.getSymbol());
 
     // Emit size directive for the size of each basic block section once we
     // get to the end of that section.
     if (MBB.isEndSection()) {
       if (!MBB.sameSection(&MF->front())) {
         if (MAI->hasDotTypeDotSizeDirective())
           emitELFSizeDirective(CurrentSectionBeginSym);
+        MBBSectionRanges[MBB.getSectionID()] =
+            MBBSectionRange{CurrentSectionBeginSym, CurrentBBEnd};
       }
     }
     emitBasicBlockEnd(MBB);
   }
 
   EmittedInsts += NumInstsInFunction;
   MachineOptimizationRemarkAnalysis R(DEBUG_TYPE, "InstructionCount",
                                       MF->getFunction().getSubprogram(),
void AsmPrinter::emitFunctionBody() {
   }
 
   for (const HandlerInfo &HI : Handlers) {
     NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                        HI.TimerGroupDescription, TimePassesIsEnabled);
     HI.Handler->markFunctionEnd();
   }
 
+  MBBSectionRanges[MF->front().getSectionID()] =
+      MBBSectionRange{CurrentFnBegin, CurrentFnEnd};
 
   // Print out jump tables referenced by the function.
   emitJumpTableInfo();
 
   // Emit post-function debug and/or EH information.
   for (const HandlerInfo &HI : Handlers) {
     NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                        HI.TimerGroupDescription, TimePassesIsEnabled);
if (!MAI->needsFunctionDescriptors()) {
     // Get the function entry point symbol.
     CurrentFnSym = OutContext.getOrCreateSymbol(
         "." + cast<MCSymbolXCOFF>(CurrentFnDescSym)->getUnqualifiedName());
   }
 
   CurrentFnSymForSize = CurrentFnSym;
   CurrentFnBegin = nullptr;
   CurrentSectionBeginSym = nullptr;
+  MBBSectionRanges.clear();
+  MBBSectionRanges.resize(
+      MBBSectionID::ToIndexFunctor::indexSize(MF.getNumBlockIDs()));
   CurExceptionSym = nullptr;
   bool NeedsLocalForSize = MAI->needsLocalForSize();
   if (F.hasFnAttribute("patchable-function-entry") ||
       F.hasFnAttribute("function-instrument") ||
       F.hasFnAttribute("xray-instruction-threshold") ||
       needFuncLabelsForEHOrDebugInfo(MF, MMI) || NeedsLocalForSize ||
       MF.getTarget().Options.EmitStackSizeSection) {
     CurrentFnBegin = createTempSymbol("func_begin");

llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp

for (const auto &I : DbgValues) {
     // so arguments are visible when breaking at function entry.
     //
     // We do not change the label for values that are described by registers,
     // as that could place them above their defining instructions. We should
     // ideally not change the labels for constant debug values either, since
     // doing that violates the ranges that are calculated in the history map.
     // However, we currently do not emit debug values for constant arguments
     // directly at the start of the function, so this code is still useful.
+    //
+    // If the first mention of an argument is in a unique-section basic block,
+    // we cannot assign the CurrentFnBegin label, as it lies in a different
+    // section. For simplicity, we simply ignore such mentions in this code.
     const DILocalVariable *DIVar =
         Entries.front().getInstr()->getDebugVariable();
     if (DIVar->isParameter() &&
-        getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
+        getDISubprogram(DIVar->getScope())->describes(&MF->getFunction()) &&
+        Entries.front().getInstr()->getParent()->sameSection(&MF->front())) {
       if (!IsDescribedByReg(Entries.front().getInstr()))
         LabelsBeforeInsn[Entries.front().getInstr()] = Asm->getFunctionBegin();
       if (Entries.front().getInstr()->getDebugExpression()->isFragment()) {
         // Mark all non-overlapping initial fragments.
         for (auto I = Entries.begin(); I != Entries.end(); ++I) {
           if (!I->isDbgValue())
             continue;
           const DIExpression *Fragment = I->getInstr()->getDebugExpression();

 void DebugHandlerBase::endFunction(const MachineFunction *MF) {
   if (hasDebugInfo(MMI, MF))
     endFunctionImpl(MF);
   DbgValues.clear();
   DbgLabels.clear();
   LabelsBeforeInsn.clear();
   LabelsAfterInsn.clear();
 }
+
+void DebugHandlerBase::beginBasicBlock(const MachineBasicBlock &MBB) {
+  if (!MBB.isBeginSection())
+    return;
+
+  PrevLabel = MBB.getSymbol();
+}
+
+void DebugHandlerBase::endBasicBlock(const MachineBasicBlock &MBB) {
+  if (!MBB.isEndSection())
+    return;
+
+  PrevLabel = nullptr;
+}

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

 }
 
 // Find DIE for the given subprogram and attach appropriate DW_AT_low_pc
 // and DW_AT_high_pc attributes. If there are global variables in this
 // scope then create and insert DIEs for these variables.
 DIE &DwarfCompileUnit::updateSubprogramScopeDIE(const DISubprogram *SP) {
   DIE *SPDie = getOrCreateSubprogramDIE(SP, includeMinimalInlineScopes());
 
+  if (!Asm->MF->hasBBSections())
     attachLowHighPC(*SPDie, Asm->getFunctionBegin(), Asm->getFunctionEnd());
+  else {
+    SmallVector<RangeSpan, 2> BB_List;
+    BB_List.push_back({Asm->getFunctionBegin(), Asm->getFunctionEnd()});
+    // If basic block sections are on, the [getFunctionBegin(),
+    // getFunctionEnd()] range will include all BBs which are in the same
+    // section as the entry block. Ranges for the other BBs have to be emitted
+    // separately.
+    for (auto &MBB : *Asm->MF) {
+      if (&MBB != &Asm->MF->front() && MBB.isBeginSection())
+        BB_List.push_back({MBB.getSymbol(),
+                           Asm->MBBSectionRanges[MBB.getSectionID()].EndLabel});
+    }
+
+    attachRangesOrLowHighPC(*SPDie, BB_List);
+  }
   if (DD->useAppleExtensionAttributes() &&
       !DD->getCurrentFunction()->getTarget().Options.DisableFramePointerElim(
           *DD->getCurrentFunction()))
     addFlag(*SPDie, dwarf::DW_AT_APPLE_omit_frame_ptr);
 
   // Only include DW_AT_frame_base in full debug info
   if (!includeMinimalInlineScopes()) {
     const TargetFrameLowering *TFI = Asm->MF->getSubtarget().getFrameLowering();
void DwarfCompileUnit::attachRangesOrLowHighPC(
   } else
     addScopeRangeList(Die, std::move(Ranges));
 }
 
 void DwarfCompileUnit::attachRangesOrLowHighPC(
     DIE &Die, const SmallVectorImpl<InsnRange> &Ranges) {
   SmallVector<RangeSpan, 2> List;
   List.reserve(Ranges.size());
-  for (const InsnRange &R : Ranges)
+  for (const InsnRange &R : Ranges) {
+    auto *BeginLabel = DD->getLabelBeforeInsn(R.first);
+    auto *EndLabel = DD->getLabelAfterInsn(R.second);
+
+    const auto *BeginMBB = R.first->getParent();
+    const auto *EndMBB = R.second->getParent();
+
+    if (BeginMBB->sameSection(EndMBB)) {
+      // If begin and end share their section, there is just one continuous
+      // range.
+      List.push_back({BeginLabel, EndLabel});
+      continue;
+    }
+
+    const auto *MBB = BeginMBB;
+    do {
+      if (MBB->sameSection(EndMBB) || MBB->isEndSection()) {
+        auto MBBSectionRange = Asm->MBBSectionRanges[MBB->getSectionID()];
         List.push_back(
-        {DD->getLabelBeforeInsn(R.first), DD->getLabelAfterInsn(R.second)});
+            {MBB->sameSection(BeginMBB) ? BeginLabel
+                                        : MBBSectionRange.BeginLabel,
+             MBB->sameSection(EndMBB) ? EndLabel : MBBSectionRange.EndLabel});
+      }
+      MBB = MBB->getNextNode();
+    } while (!MBB->sameSection(EndMBB));
+  }
   attachRangesOrLowHighPC(Die, std::move(List));
 }
 
 // This scope represents inlined body of a function. Construct DIE to
 // represent this concrete inlined copy of the function.
 DIE *DwarfCompileUnit::constructInlinedScopeDIE(LexicalScope *Scope) {
   assert(Scope->getScopeNode());
   auto *DS = Scope->getScopeNode();

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

for (auto EB = Entries.begin(), EI = EB, EE = Entries.end(); EI != EE; ++EI) {
     // a location list entry starting after the clobbering instruction.
     const MCSymbol *StartLabel =
         EI->isClobber() ? getLabelAfterInsn(Instr) : getLabelBeforeInsn(Instr);
     assert(StartLabel &&
            "Forgot label before/after instruction starting a range!");
 
     const MCSymbol *EndLabel;
     if (std::next(EI) == Entries.end()) {
-      EndLabel = Asm->getFunctionEnd();
+      const MachineBasicBlock &EndMBB = Asm->MF->back();
+      EndLabel = Asm->MBBSectionRanges[EndMBB.getSectionID()].EndLabel;
       if (EI->isClobber())
         EndMI = EI->getInstr();
     }
     else if (std::next(EI)->isClobber())
       EndLabel = getLabelAfterInsn(std::next(EI)->getInstr());
     else
       EndLabel = getLabelBeforeInsn(std::next(EI)->getInstr());
     assert(EndLabel && "Forgot label after instruction ending a range!");
if (TheCU.getCUNode()->isDebugDirectivesOnly()) {
     PrevLabel = nullptr;
     CurFn = nullptr;
     return;
   }
 
   DenseSet<InlinedEntity> Processed;
   collectEntityInfo(TheCU, SP, Processed);
 
   // Add the range of this function to the list of ranges for the CU.
   TheCU.addRange({Asm->getFunctionBegin(), Asm->getFunctionEnd()});
 
+  // With basic block sections, add ranges for all basic block sections.
+  if (MF->hasBBSections()) {
+    for (auto &MBB : *MF) {
+      if (&MBB != &MF->front() && MBB.isBeginSection())
+        TheCU.addRange({MBB.getSymbol(),
+                        Asm->MBBSectionRanges[MBB.getSectionID()].EndLabel});
+    }
+  }
+
   // Under -gmlt, skip building the subprogram if there are no inlined
   // subroutines inside it. But with -fdebug-info-for-profiling, the subprogram
   // is still needed as we need its source location.
   if (!TheCU.getCUNode()->getDebugInfoForProfiling() &&
       TheCU.getCUNode()->getEmissionKind() == DICompileUnit::LineTablesOnly &&
       LScopes.getAbstractScopesList().empty() && !IsDarwin) {
     assert(InfoHolder.getScopeVariables().empty());
     PrevLabel = nullptr;
     CurFn = nullptr;

llvm/test/DebugInfo/X86/basicblock-sections_1.ll

+; RUN: llc -O0 %s -mtriple=x86_64-* -filetype=obj -o %t && llvm-dwarfdump  -debug-abbrev %t | FileCheck --check-prefix=NO-SECTIONS %s
+; RUN: llc -O0 %s --basicblock-sections=all -mtriple=x86_64-* -filetype=obj -o %t && llvm-dwarfdump  -debug-abbrev %t | FileCheck --check-prefix=BB-SECTIONS %s
+; RUN: llc -O0 %s --basicblock-sections=all -mtriple=x86_64-* -filetype=obj -split-dwarf-file=%t.dwo -o %t && llvm-dwarfdump  -debug-abbrev %t | FileCheck --check-prefix=BB-SECTIONS %s
+
+; From:
+; int foo(int a) {
+;   if (a > 20)
+;     return 2;
+;   else
+;     return 0;
+; }
+
+; NO-SECTIONS: DW_AT_low_pc     DW_FORM_addr
+; NO-SECTIONS: DW_AT_high_pc    DW_FORM_data4
+; BB-SECTIONS: DW_AT_low_pc     DW_FORM_addr
+; BB-SECTIONS: DW_AT_ranges DW_FORM_sec_offset
+
+; Function Attrs: noinline nounwind optnone uwtable
+define dso_local i32 @_Z3fooi(i32 %0) !dbg !7 {
+  %2 = alloca i32, align 4
+  %3 = alloca i32, align 4
+  store i32 %0, i32* %3, align 4
+  call void @llvm.dbg.declare(metadata i32* %3, metadata !11, metadata !DIExpression()), !dbg !12
+  %4 = load i32, i32* %3, align 4, !dbg !13
+  %5 = icmp sgt i32 %4, 20, !dbg !15
+  br i1 %5, label %6, label %7, !dbg !16
+
+6:                                                ; preds = %1
+  store i32 2, i32* %2, align 4, !dbg !17
+  br label %8, !dbg !17
+
+7:                                                ; preds = %1
+  store i32 0, i32* %2, align 4, !dbg !18
+  br label %8, !dbg !18
+
+8:                                                ; preds = %7, %6
+  %9 = load i32, i32* %2, align 4, !dbg !19
+  ret i32 %9, !dbg !19
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 10.0.0 ([e-mail]:google/llvm-propeller.git f9421ebf4b3d8b64678bf6c49d1607fdce3f50c5)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "debuginfo.cc", directory: "/")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!7 = distinct !DISubprogram(name: "foo", linkageName: "_Z3fooi", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!12 = !DILocation(line: 1, column: 13, scope: !7)
+!13 = !DILocation(line: 2, column: 7, scope: !14)
+!14 = distinct !DILexicalBlock(scope: !7, file: !1, line: 2, column: 7)
+!15 = !DILocation(line: 2, column: 9, scope: !14)
+!16 = !DILocation(line: 2, column: 7, scope: !7)
+!17 = !DILocation(line: 3, column: 5, scope: !14)
+!18 = !DILocation(line: 5, column: 5, scope: !14)
+!19 = !DILocation(line: 6, column: 1, scope: !7)