Revert "[DWARF] Add cuttoff guarding quadratic validThroughout behaviour"

This reverts commit b9d977b.

This cutoff is no longer required. The commit 34ffa7fc501 (D86153) introduces a
performance improvement which was tested against the motivating case for this
patch.

Discussed in differential revision: https://reviews.llvm.org/D86153

Author: OCHyams

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -148,11 +148,6 @@ static cl::opt<LinkageNameOption>
                                             "Abstract subprograms")),
                       cl::init(DefaultLinkageNames));
 
-static cl::opt<unsigned> LocationAnalysisSizeLimit(
-    "singlevarlocation-input-bb-limit",
-    cl::desc("Maximum block size to analyze for single-location variables"),
-    cl::init(30000), cl::Hidden);
-
 static const char *const DWARFGroupName = "dwarf";
 static const char *const DWARFGroupDescription = "DWARF Emission";
 static const char *const DbgTimerName = "writer";
@@ -1611,10 +1606,8 @@ static bool validThroughout(LexicalScopes &LScopes,
 // [1-3)    [(reg0, fragment 0, 32), (reg1, fragment 32, 32)]
 // [3-4)    [(reg1, fragment 32, 32), (123, fragment 64, 32)]
 // [4-)     [(@g, fragment 0, 96)]
-bool DwarfDebug::buildLocationList(
-    SmallVectorImpl<DebugLocEntry> &DebugLoc,
-    const DbgValueHistoryMap::Entries &Entries,
-    DenseSet<const MachineBasicBlock *> &VeryLargeBlocks) {
+bool DwarfDebug::buildLocationList(SmallVectorImpl<DebugLocEntry> &DebugLoc,
+                                   const DbgValueHistoryMap::Entries &Entries) {
   using OpenRange =
       std::pair<DbgValueHistoryMap::EntryIndex, DbgValueLoc>;
   SmallVector<OpenRange, 4> OpenRanges;
@@ -1710,14 +1703,8 @@ bool DwarfDebug::buildLocationList(
       DebugLoc.pop_back();
   }
 
-  // If there's a single entry, safe for a single location, and not part of
-  // an over-sized basic block, then ask validThroughout whether this
-  // location can be represented as a single variable location.
-  if (DebugLoc.size() != 1 || !isSafeForSingleLocation)
-    return false;
-  if (VeryLargeBlocks.count(StartDebugMI->getParent()))
-    return false;
-  return validThroughout(LScopes, StartDebugMI, EndMI, getInstOrdering());
+  return DebugLoc.size() == 1 && isSafeForSingleLocation &&
+         validThroughout(LScopes, StartDebugMI, EndMI, getInstOrdering());
 }
 
 DbgEntity *DwarfDebug::createConcreteEntity(DwarfCompileUnit &TheCU,
@@ -1749,13 +1736,6 @@ void DwarfDebug::collectEntityInfo(DwarfCompileUnit &TheCU,
   // Grab the variable info that was squirreled away in the MMI side-table.
   collectVariableInfoFromMFTable(TheCU, Processed);
 
-  // Identify blocks that are unreasonably sized, so that we can later
-  // skip lexical scope analysis over them.
-  DenseSet<const MachineBasicBlock *> VeryLargeBlocks;
-  for (const auto &MBB : *CurFn)
-    if (MBB.size() > LocationAnalysisSizeLimit)
-      VeryLargeBlocks.insert(&MBB);
-
   for (const auto &I : DbgValues) {
     InlinedEntity IV = I.first;
     if (Processed.count(IV))
@@ -1792,8 +1772,7 @@ void DwarfDebug::collectEntityInfo(DwarfCompileUnit &TheCU,
     if (HistSize == 1 || SingleValueWithClobber) {
       const auto *End =
           SingleValueWithClobber ? HistoryMapEntries[1].getInstr() : nullptr;
-      if (VeryLargeBlocks.count(MInsn->getParent()) == 0 &&
-          validThroughout(LScopes, MInsn, End, getInstOrdering())) {
+      if (validThroughout(LScopes, MInsn, End, getInstOrdering())) {
         RegVar->initializeDbgValue(MInsn);
         continue;
       }
@@ -1808,8 +1787,7 @@ void DwarfDebug::collectEntityInfo(DwarfCompileUnit &TheCU,
 
     // Build the location list for this variable.
     SmallVector<DebugLocEntry, 8> Entries;
-    bool isValidSingleLocation =
-        buildLocationList(Entries, HistoryMapEntries, VeryLargeBlocks);
+    bool isValidSingleLocation = buildLocationList(Entries, HistoryMapEntries);
 
     // Check whether buildLocationList managed to merge all locations to one
     // that is valid throughout the variable's scope. If so, produce single

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h

@@ -598,10 +598,8 @@ class DwarfDebug : public DebugHandlerBase {
   /// function that describe the same variable. If the resulting 
   /// list has only one entry that is valid for entire variable's
   /// scope return true.
-  bool buildLocationList(
-      SmallVectorImpl<DebugLocEntry> &DebugLoc,
-      const DbgValueHistoryMap::Entries &Entries,
-      DenseSet<const MachineBasicBlock *> &VeryLargeBlocks);
+  bool buildLocationList(SmallVectorImpl<DebugLocEntry> &DebugLoc,
+                         const DbgValueHistoryMap::Entries &Entries);
 
   /// Collect variable information from the side table maintained by MF.
   void collectVariableInfoFromMFTable(DwarfCompileUnit &TheCU,