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

This reverts commit b9d977b0ca.

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

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,

llvm/test/DebugInfo/MIR/X86/singlelocation-cutoffs.mir

@@ -1,65 +0,0 @@
-# Test cutoffs for single-location variable analysis.
-# Disable validThroughout if the input size exceeds the specified limit
-
-# RUN: llc %s -o - -start-after=livedebugvalues -mtriple=x86_64-unknown-unknown \
-# RUN:   --singlevarlocation-input-bb-limit=0 -filetype=obj\
-# RUN:   | llvm-dwarfdump -v -\
-# RUN:   | FileCheck %s -check-prefix=LIMITED
-
-# RUN: llc %s -o - -start-after=livedebugvalues -mtriple=x86_64-unknown-unknown \
-# RUN: --singlevarlocation-input-bb-limit=20 -filetype=obj | llvm-dwarfdump -v -\
-# RUN:   | FileCheck %s -check-prefix=UNLIMITED
-
-# LIMITED: DW_AT_location [DW_FORM_sec_offset]
-
-# UNLIMITED: DW_AT_location [DW_FORM_exprloc]
-
---- |
-  target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
-
-  declare i32 @use(i32)
-
-  define i32 @foo(i32 %x) !dbg !6 {
-  entry:
-    ret i32 1, !dbg !15
-  }
-
-  declare void @llvm.dbg.value(metadata, metadata, metadata)
-
-  !llvm.dbg.cu = !{!0}
-  !llvm.debugify = !{!3, !4}
-  !llvm.module.flags = !{!5}
-
-  !0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
-  !1 = !DIFile(filename: "/tmp/t.ll", directory: "/")
-  !2 = !{}
-  !3 = !{i32 4}
-  !4 = !{i32 2}
-  !5 = !{i32 2, !"Debug Info Version", i32 3}
-  !6 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
-  !7 = !DISubroutineType(types: !2)
-  !8 = !{!9, !11}
-  !9 = !DILocalVariable(name: "1", scope: !6, file: !1, line: 1, type: !10)
-  !10 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
-  !11 = !DILocalVariable(name: "2", scope: !6, file: !1, line: 3, type: !10)
-  !12 = !DILocation(line: 1, column: 1, scope: !6)
-  !13 = !DILocation(line: 2, column: 1, scope: !6)
-  !14 = !DILocation(line: 3, column: 1, scope: !6)
-  !15 = !DILocation(line: 4, column: 1, scope: !6)
-
-...
----
-name:            foo
-liveins:
-  - { reg: '$edi', virtual-reg: '' }
-stack:
-  - { id: 0, name: '', type: spill-slot, offset: -12, size: 4, alignment: 4,
-      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
-      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
-body:             |
-  bb.0.entry:
-    liveins: $edi
-    DBG_VALUE renamable $edi, $noreg, !11, !DIExpression(), debug-location !14
-    RETQ debug-location !14
-
-...