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llvm-project/llvm/tools/llvm-dwarfdump/Statistics.cpp

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#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/DebugInfo/DIContext.h"
#include "llvm/DebugInfo/DWARF/DWARFContext.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugLoc.h"
#include "llvm/Object/ObjectFile.h"
#define DEBUG_TYPE "dwarfdump"
using namespace llvm;
using namespace object;
/// Holds statistics for one function (or other entity that has a PC range and
/// contains variables, such as a compile unit).
struct PerFunctionStats {
/// Number of inlined instances of this function.
unsigned NumFnInlined = 0;
/// Number of variables with location across all inlined instances.
unsigned TotalVarWithLoc = 0;
/// Number of constants with location across all inlined instances.
unsigned ConstantMembers = 0;
/// List of all Variables in this function.
StringSet<> VarsInFunction;
/// Compile units also cover a PC range, but have this flag set to false.
bool IsFunction = false;
};
/// Holds accumulated global statistics about DIEs.
struct GlobalStats {
/// Total number of PC range bytes covered by DW_AT_locations.
unsigned ScopeBytesCovered = 0;
/// Total number of PC range bytes in each variable's enclosing scope,
/// starting from the first definition of the variable.
unsigned ScopeBytesFromFirstDefinition = 0;
/// Total number of call site entries (DW_TAG_call_site).
unsigned CallSiteEntries = 0;
/// Total byte size of concrete functions. This byte size includes
/// inline functions contained in the concrete functions.
uint64_t FunctionSize = 0;
/// Total byte size of inlined functions. This is the total number of bytes
/// for the top inline functions within concrete functions. This can help
/// tune the inline settings when compiling to match user expectations.
uint64_t InlineFunctionSize = 0;
};
/// Extract the low pc from a Die.
static uint64_t getLowPC(DWARFDie Die) {
auto RangesOrError = Die.getAddressRanges();
DWARFAddressRangesVector Ranges;
if (RangesOrError)
Ranges = RangesOrError.get();
else
llvm::consumeError(RangesOrError.takeError());
if (Ranges.size())
return Ranges[0].LowPC;
return dwarf::toAddress(Die.find(dwarf::DW_AT_low_pc), 0);
}
/// Collect debug info quality metrics for one DIE.
static void collectStatsForDie(DWARFDie Die, std::string FnPrefix,
std::string VarPrefix, uint64_t ScopeLowPC,
uint64_t BytesInScope,
uint32_t InlineDepth,
StringMap<PerFunctionStats> &FnStatMap,
GlobalStats &GlobalStats) {
bool HasLoc = false;
uint64_t BytesCovered = 0;
uint64_t OffsetToFirstDefinition = 0;
if (Die.getTag() == dwarf::DW_TAG_call_site) {
GlobalStats.CallSiteEntries++;
return;
}
if (Die.getTag() != dwarf::DW_TAG_formal_parameter &&
Die.getTag() != dwarf::DW_TAG_variable &&
Die.getTag() != dwarf::DW_TAG_member) {
// Not a variable or constant member.
return;
}
if (Die.find(dwarf::DW_AT_const_value)) {
// This catches constant members *and* variables.
HasLoc = true;
BytesCovered = BytesInScope;
} else {
if (Die.getTag() == dwarf::DW_TAG_member) {
// Non-const member.
return;
}
// Handle variables and function arguments.
auto FormValue = Die.find(dwarf::DW_AT_location);
HasLoc = FormValue.hasValue();
if (HasLoc) {
// Get PC coverage.
if (auto DebugLocOffset = FormValue->getAsSectionOffset()) {
auto *DebugLoc = Die.getDwarfUnit()->getContext().getDebugLoc();
if (auto List = DebugLoc->getLocationListAtOffset(*DebugLocOffset)) {
for (auto Entry : List->Entries)
BytesCovered += Entry.End - Entry.Begin;
if (List->Entries.size()) {
uint64_t FirstDef = List->Entries[0].Begin;
uint64_t UnitOfs = getLowPC(Die.getDwarfUnit()->getUnitDIE());
// Ranges sometimes start before the lexical scope.
if (UnitOfs + FirstDef >= ScopeLowPC)
OffsetToFirstDefinition = UnitOfs + FirstDef - ScopeLowPC;
// Or even after it. Count that as a failure.
if (OffsetToFirstDefinition > BytesInScope)
OffsetToFirstDefinition = 0;
}
}
assert(BytesInScope);
} else {
// Assume the entire range is covered by a single location.
BytesCovered = BytesInScope;
}
}
}
// Collect PC range coverage data.
auto &FnStats = FnStatMap[FnPrefix];
if (DWARFDie D =
Die.getAttributeValueAsReferencedDie(dwarf::DW_AT_abstract_origin))
Die = D;
// By using the variable name + the path through the lexical block tree, the
// keys are consistent across duplicate abstract origins in different CUs.
std::string VarName = StringRef(Die.getName(DINameKind::ShortName));
FnStats.VarsInFunction.insert(VarPrefix+VarName);
if (BytesInScope) {
FnStats.TotalVarWithLoc += (unsigned)HasLoc;
// Adjust for the fact the variables often start their lifetime in the
// middle of the scope.
BytesInScope -= OffsetToFirstDefinition;
// Turns out we have a lot of ranges that extend past the lexical scope.
GlobalStats.ScopeBytesCovered += std::min(BytesInScope, BytesCovered);
GlobalStats.ScopeBytesFromFirstDefinition += BytesInScope;
assert(GlobalStats.ScopeBytesCovered <=
GlobalStats.ScopeBytesFromFirstDefinition);
} else {
FnStats.ConstantMembers++;
}
}
/// Recursively collect debug info quality metrics.
static void collectStatsRecursive(DWARFDie Die, std::string FnPrefix,
std::string VarPrefix, uint64_t ScopeLowPC,
uint64_t BytesInScope,
uint32_t InlineDepth,
StringMap<PerFunctionStats> &FnStatMap,
GlobalStats &GlobalStats) {
// Handle any kind of lexical scope.
const dwarf::Tag Tag = Die.getTag();
const bool IsFunction = Tag == dwarf::DW_TAG_subprogram;
const bool IsBlock = Tag == dwarf::DW_TAG_lexical_block;
const bool IsInlinedFunction = Tag == dwarf::DW_TAG_inlined_subroutine;
if (IsFunction || IsInlinedFunction || IsBlock) {
// Reset VarPrefix when entering a new function.
if (Die.getTag() == dwarf::DW_TAG_subprogram ||
Die.getTag() == dwarf::DW_TAG_inlined_subroutine)
VarPrefix = "v";
// Ignore forward declarations.
if (Die.find(dwarf::DW_AT_declaration))
return;
// Count the function.
if (!IsBlock) {
StringRef Name = Die.getName(DINameKind::LinkageName);
if (Name.empty())
Name = Die.getName(DINameKind::ShortName);
FnPrefix = Name;
// Skip over abstract origins.
if (Die.find(dwarf::DW_AT_inline))
return;
// We've seen an (inlined) instance of this function.
auto &FnStats = FnStatMap[Name];
FnStats.NumFnInlined++;
FnStats.IsFunction = true;
}
// PC Ranges.
auto RangesOrError = Die.getAddressRanges();
if (!RangesOrError) {
llvm::consumeError(RangesOrError.takeError());
return;
}
auto Ranges = RangesOrError.get();
uint64_t BytesInThisScope = 0;
for (auto Range : Ranges)
BytesInThisScope += Range.HighPC - Range.LowPC;
ScopeLowPC = getLowPC(Die);
if (BytesInThisScope) {
BytesInScope = BytesInThisScope;
if (IsFunction)
GlobalStats.FunctionSize += BytesInThisScope;
else if (IsInlinedFunction && InlineDepth == 0)
GlobalStats.InlineFunctionSize += BytesInThisScope;
}
} else {
// Not a scope, visit the Die itself. It could be a variable.
collectStatsForDie(Die, FnPrefix, VarPrefix, ScopeLowPC, BytesInScope,
InlineDepth, FnStatMap, GlobalStats);
}
// Set InlineDepth correctly for child recursion
if (IsFunction)
InlineDepth = 0;
else if (IsInlinedFunction)
++InlineDepth;
// Traverse children.
unsigned LexicalBlockIndex = 0;
DWARFDie Child = Die.getFirstChild();
while (Child) {
std::string ChildVarPrefix = VarPrefix;
if (Child.getTag() == dwarf::DW_TAG_lexical_block)
ChildVarPrefix += toHex(LexicalBlockIndex++) + '.';
collectStatsRecursive(Child, FnPrefix, ChildVarPrefix, ScopeLowPC,
BytesInScope, InlineDepth, FnStatMap, GlobalStats);
Child = Child.getSibling();
}
}
/// Print machine-readable output.
/// The machine-readable format is single-line JSON output.
/// \{
static void printDatum(raw_ostream &OS, const char *Key, StringRef Value) {
OS << ",\"" << Key << "\":\"" << Value << '"';
LLVM_DEBUG(llvm::dbgs() << Key << ": " << Value << '\n');
}
static void printDatum(raw_ostream &OS, const char *Key, uint64_t Value) {
OS << ",\"" << Key << "\":" << Value;
LLVM_DEBUG(llvm::dbgs() << Key << ": " << Value << '\n');
}
/// \}
/// Collect debug info quality metrics for an entire DIContext.
///
/// Do the impossible and reduce the quality of the debug info down to a few
/// numbers. The idea is to condense the data into numbers that can be tracked
/// over time to identify trends in newer compiler versions and gauge the effect
/// of particular optimizations. The raw numbers themselves are not particularly
/// useful, only the delta between compiling the same program with different
/// compilers is.
bool collectStatsForObjectFile(ObjectFile &Obj, DWARFContext &DICtx,
Twine Filename, raw_ostream &OS) {
StringRef FormatName = Obj.getFileFormatName();
GlobalStats GlobalStats;
StringMap<PerFunctionStats> Statistics;
for (const auto &CU : static_cast<DWARFContext *>(&DICtx)->compile_units())
if (DWARFDie CUDie = CU->getUnitDIE(false))
collectStatsRecursive(CUDie, "/", "g", 0, 0, 0, Statistics, GlobalStats);
/// The version number should be increased every time the algorithm is changed
/// (including bug fixes). New metrics may be added without increasing the
/// version.
unsigned Version = 1;
unsigned VarTotal = 0;
unsigned VarUnique = 0;
unsigned VarWithLoc = 0;
unsigned NumFunctions = 0;
unsigned NumInlinedFunctions = 0;
for (auto &Entry : Statistics) {
PerFunctionStats &Stats = Entry.getValue();
unsigned TotalVars = Stats.VarsInFunction.size() * Stats.NumFnInlined;
unsigned Constants = Stats.ConstantMembers;
VarWithLoc += Stats.TotalVarWithLoc + Constants;
VarTotal += TotalVars + Constants;
VarUnique += Stats.VarsInFunction.size();
LLVM_DEBUG(for (auto &V : Stats.VarsInFunction) llvm::dbgs()
<< Entry.getKey() << ": " << V.getKey() << "\n");
NumFunctions += Stats.IsFunction;
NumInlinedFunctions += Stats.IsFunction * Stats.NumFnInlined;
}
// Print summary.
OS.SetBufferSize(1024);
OS << "{\"version\":" << Version;
LLVM_DEBUG(llvm::dbgs() << "Variable location quality metrics\n";
llvm::dbgs() << "---------------------------------\n");
printDatum(OS, "file", Filename.str());
printDatum(OS, "format", FormatName);
printDatum(OS, "source functions", NumFunctions);
printDatum(OS, "inlined functions", NumInlinedFunctions);
printDatum(OS, "unique source variables", VarUnique);
printDatum(OS, "source variables", VarTotal);
printDatum(OS, "variables with location", VarWithLoc);
printDatum(OS, "call site entries", GlobalStats.CallSiteEntries);
printDatum(OS, "scope bytes total",
GlobalStats.ScopeBytesFromFirstDefinition);
printDatum(OS, "scope bytes covered", GlobalStats.ScopeBytesCovered);
printDatum(OS, "total function size", GlobalStats.FunctionSize);
printDatum(OS, "total inlined function size", GlobalStats.InlineFunctionSize);
OS << "}\n";
LLVM_DEBUG(
llvm::dbgs() << "Total Availability: "
<< (int)std::round((VarWithLoc * 100.0) / VarTotal) << "%\n";
llvm::dbgs() << "PC Ranges covered: "
<< (int)std::round((GlobalStats.ScopeBytesCovered * 100.0) /
GlobalStats.ScopeBytesFromFirstDefinition)
<< "%\n");
return true;
}
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