[llvm] [llvm-objdump] Optimize live element tracking (PR #158763)

[James Henderson via llvm-commits]

================
@@ -239,57 +302,116 @@ void LiveElementPrinter::addCompileUnit(DWARFDie D) {
 void LiveElementPrinter::update(object::SectionedAddress ThisAddr,
                                 object::SectionedAddress NextAddr,
                                 bool IncludeDefinedVars) {
-  // Do not create live ranges when debug-inlined-funcs option is provided with
-  // line format option.
+  // Exit early if only printing function limits.
   if (DbgInlinedFunctions == DFLimitsOnly)
     return;
 
-  // First, check variables which have already been assigned a column, so
-  // that we don't change their order.
-  SmallSet<unsigned, 8> CheckedElementIdxs;
+  // Free columns identified in the previous cycle.
+  for (unsigned ColIdx : ColumnsToFreeNextCycle)
+    freeColumn(ColIdx);
+  ColumnsToFreeNextCycle.clear();
+
+  // Update status of active columns and collect those to free next cycle.
   for (unsigned ColIdx = 0, End = ActiveCols.size(); ColIdx < End; ++ColIdx) {
     if (!ActiveCols[ColIdx].isActive())
       continue;
 
-    CheckedElementIdxs.insert(ActiveCols[ColIdx].ElementIdx);
     const std::unique_ptr<LiveElement> &LE =
         LiveElements[ActiveCols[ColIdx].ElementIdx];
     ActiveCols[ColIdx].LiveIn = LE->liveAtAddress(ThisAddr);
     ActiveCols[ColIdx].LiveOut = LE->liveAtAddress(NextAddr);
-    std::string Name = Demangle ? demangle(LE->getName()) : LE->getName();
-    LLVM_DEBUG(dbgs() << "pass 1, " << ThisAddr.Address << "-"
-                      << NextAddr.Address << ", " << Name << ", Col " << ColIdx
-                      << ": LiveIn=" << ActiveCols[ColIdx].LiveIn
-                      << ", LiveOut=" << ActiveCols[ColIdx].LiveOut << "\n");
 
-    if (!ActiveCols[ColIdx].LiveIn && !ActiveCols[ColIdx].LiveOut)
+    LLVM_DEBUG({
+      std::string Name = Demangle ? demangle(LE->getName()) : LE->getName();
+      dbgs() << "pass 1, " << ThisAddr.Address << "-" << NextAddr.Address
+             << ", " << Name << ", Col " << ColIdx
+             << ": LiveIn=" << ActiveCols[ColIdx].LiveIn
+             << ", LiveOut=" << ActiveCols[ColIdx].LiveOut << "\n";
+    });
+
+    // If element is fully dead, deactivate column immediately.
+    if (!ActiveCols[ColIdx].LiveIn && !ActiveCols[ColIdx].LiveOut) {
       ActiveCols[ColIdx].ElementIdx = Column::NullElementIdx;
+      continue;
+    }
+
+    // Mark for cleanup in the next cycle if range ends here.
+    if (ActiveCols[ColIdx].LiveIn && !ActiveCols[ColIdx].LiveOut)
+      ColumnsToFreeNextCycle.push_back(ColIdx);
   }
 
   // Next, look for variables which don't already have a column, but which
-  // are now live.
+  // are now live (those starting at ThisAddr or NextAddr).
   if (IncludeDefinedVars) {
-    for (unsigned ElementIdx = 0, End = LiveElements.size(); ElementIdx < End;
-         ++ElementIdx) {
-      if (CheckedElementIdxs.count(ElementIdx))
+    // Collect all elements starting at ThisAddr and NextAddr.
+    std::vector<std::pair<unsigned, LiveElement *>> NewLiveElements;
+    auto CollectNewElements = [&](const auto &It) {
+      if (It == LiveElementsByAddress.end())
+        return;
+
+      const std::vector<LiveElement *> &ElementList = It->second;
+      // Get the ElementIdx for sorting and column management.
----------------
jh7370 wrote:

Rather than refer to the variable name (which you don't even use until later), just use the real term, i.e. something like "element index".

https://github.com/llvm/llvm-project/pull/158763