[NFC][llvm-dwarfdump] Don't calculate unnecessary stats

[djtodoro]

Summary

Small optimization of the code -- No need to calculate any stats for NULL nodes, and also no need to call the collectStatsForDie() if it is the CU itself.

[aprantl]

This definitely won't hurt, but it's a bit inconsistent. The NULL check is inside collectStatsRecursive(), but the CU check is outside of collectStatsForDie(). It would be nice to be consistent and have all functions handle all DIE types with potentially an early exit at the top rather sometimes having the burden to sanitize the input at the call site.

[djtodoro]

• Use early exit in both funcs

[djtodoro]

In D96871#2568791, @aprantl wrote:

This definitely won't hurt, but it's a bit inconsistent. The NULL check is inside collectStatsRecursive(), but the CU check is outside of collectStatsForDie(). It would be nice to be consistent and have all functions handle all DIE types with potentially an early exit at the top rather sometimes having the burden to sanitize the input at the call site.

I agree. Thanks.

[djtodoro]

@aprantl I guess this is ok now ? :)

[djtodoro]

Thanks!

llvm/tools/llvm-dwarfdump/Statistics.cpp

 /// Collect debug info quality metrics for one DIE.
 static void collectStatsForDie(DWARFDie Die, std::string FnPrefix,
                                std::string VarPrefix, uint64_t BytesInScope,
                                uint32_t InlineDepth,
                                StringMap<PerFunctionStats> &FnStatMap,
                                GlobalStats &GlobalStats,
                                LocationStats &LocStats,
                                InlinedVarsTy *InlinedVariables) {
+  const dwarf::Tag Tag = Die.getTag();
+  // Skip CU node.
+  if (Tag == dwarf::DW_TAG_compile_unit)
+    return;
+
   bool HasLoc = false;
   bool HasSrcLoc = false;
   bool HasType = false;
   uint64_t TotalBytesCovered = 0;
   uint64_t ScopeBytesCovered = 0;
   uint64_t BytesEntryValuesCovered = 0;
   auto &FnStats = FnStatMap[FnPrefix];
-  bool IsParam = Die.getTag() == dwarf::DW_TAG_formal_parameter;
-  bool IsLocalVar = Die.getTag() == dwarf::DW_TAG_variable;
-  bool IsConstantMember = Die.getTag() == dwarf::DW_TAG_member &&
+  bool IsParam = Tag == dwarf::DW_TAG_formal_parameter;
+  bool IsLocalVar = Tag == dwarf::DW_TAG_variable;
+  bool IsConstantMember = Tag == dwarf::DW_TAG_member &&
                           Die.find(dwarf::DW_AT_const_value);
 
   // For zero covered inlined variables the locstats will be
   // calculated later.
   bool DeferLocStats = false;
 
-  if (Die.getTag() == dwarf::DW_TAG_call_site ||
-      Die.getTag() == dwarf::DW_TAG_GNU_call_site) {
+  if (Tag == dwarf::DW_TAG_call_site || Tag == dwarf::DW_TAG_GNU_call_site) {
     GlobalStats.CallSiteDIEs++;
     return;
   }
 
-  if (Die.getTag() == dwarf::DW_TAG_call_site_parameter ||
-      Die.getTag() == dwarf::DW_TAG_GNU_call_site_parameter) {
+  if (Tag == dwarf::DW_TAG_call_site_parameter ||
+      Tag == dwarf::DW_TAG_GNU_call_site_parameter) {
     GlobalStats.CallSiteParamDIEs++;
     return;
   }
 
   if (!IsParam && !IsLocalVar && !IsConstantMember) {
     // Not a variable or constant member.
     return;
   }
static void collectStatsRecursive(DWARFDie Die, std::string FnPrefix,
                                   std::string VarPrefix, uint64_t BytesInScope,
                                   uint32_t InlineDepth,
                                   StringMap<PerFunctionStats> &FnStatMap,
                                   GlobalStats &GlobalStats,
                                   LocationStats &LocStats,
                                   InlinedVarsTyMap &GlobalInlinedFnInfo,
                                   InlinedFnInstacesTy &InlinedFnsToBeProcessed,
                                   InlinedVarsTy *InlinedVarsPtr = nullptr) {
+  // Skip NULL nodes.
+  if (Die.isNULL())
+    return;
+
   const dwarf::Tag Tag = Die.getTag();
   // Skip function types.
   if (Tag == dwarf::DW_TAG_subroutine_type)
     return;
 
   // Handle any kind of lexical scope.
   const bool IsFunction = Tag == dwarf::DW_TAG_subprogram;
   const bool IsBlock = Tag == dwarf::DW_TAG_lexical_block;