Revert "Emit correct location lists with basic block sections."

Breaks check-llvm on non-linux, see comments on https://reviews.llvm.org/D85085
This reverts commit caae570
and follow-up commit 1546c52.

Author: abhinavgaba

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -1357,9 +1357,11 @@ void AsmPrinter::emitFunctionBody() {
 
     // We must emit temporary symbol for the end of this basic block, if either
     // we have BBLabels enabled or if this basic blocks marks the end of a
-    // section.
+    // section (except the section containing the entry basic block as the end
+    // symbol for that section is CurrentFnEnd).
     if (MF->hasBBLabels() ||
-        (MAI->hasDotTypeDotSizeDirective() && MBB.isEndSection()))
+        (MAI->hasDotTypeDotSizeDirective() && MBB.isEndSection() &&
+         !MBB.sameSection(&MF->front())))
       OutStreamer->emitLabel(MBB.getEndSymbol());
 
     if (MBB.isEndSection()) {

llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp

@@ -290,10 +290,16 @@ void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
     // doing that violates the ranges that are calculated in the history map.
     // However, we currently do not emit debug values for constant arguments
     // directly at the start of the function, so this code is still useful.
+    // FIXME: If the first mention of an argument is in a unique section basic
+    // block, we cannot always assign the CurrentFnBeginLabel as it lies in a
+    // different section.  Temporarily, we disable generating loc list
+    // information or DW_AT_const_value when the block is in a different
+    // section.
     const DILocalVariable *DIVar =
         Entries.front().getInstr()->getDebugVariable();
     if (DIVar->isParameter() &&
-        getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
+        getDISubprogram(DIVar->getScope())->describes(&MF->getFunction()) &&
+        Entries.front().getInstr()->getParent()->sameSection(&MF->front())) {
       if (!IsDescribedByReg(Entries.front().getInstr()))
         LabelsBeforeInsn[Entries.front().getInstr()] = Asm->getFunctionBegin();
       if (Entries.front().getInstr()->getDebugExpression()->isFragment()) {
@@ -379,25 +385,22 @@ void DebugHandlerBase::endInstruction() {
 
   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
       LabelsAfterInsn.find(CurMI);
+  CurMI = nullptr;
 
-  // No label needed or label already assigned.
-  if (I == LabelsAfterInsn.end() || I->second) {
-    CurMI = nullptr;
+  // No label needed.
+  if (I == LabelsAfterInsn.end())
     return;
-  }
 
-  // We need a label after this instruction.  With basic block sections, just
-  // use the end symbol of the section if this is the last instruction of the
-  // section.  This reduces the need for an additional label and also helps
-  // merging ranges.
-  if (CurMI->getParent()->isEndSection() && CurMI->getNextNode() == nullptr) {
-    PrevLabel = CurMI->getParent()->getEndSymbol();
-  } else if (!PrevLabel) {
+  // Label already assigned.
+  if (I->second)
+    return;
+
+  // We need a label after this instruction.
+  if (!PrevLabel) {
     PrevLabel = MMI->getContext().createTempSymbol();
     Asm->OutStreamer->emitLabel(PrevLabel);
   }
   I->second = PrevLabel;
-  CurMI = nullptr;
 }
 
 void DebugHandlerBase::endFunction(const MachineFunction *MF) {

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -1741,30 +1741,7 @@ bool DwarfDebug::buildLocationList(SmallVectorImpl<DebugLocEntry> &DebugLoc,
     SmallVector<DbgValueLoc, 4> Values;
     for (auto &R : OpenRanges)
       Values.push_back(R.second);
-
-    // With Basic block sections, it is posssible that the StartLabel and the
-    // Instr are not in the same section.  This happens when the StartLabel is
-    // the function begin label and the dbg value appears in a basic block
-    // that is not the entry.  In this case, the range needs to be split to
-    // span each individual section in the range from StartLabel to EndLabel.
-    if (Asm->MF->hasBBSections() && StartLabel == Asm->getFunctionBegin() &&
-        !Instr->getParent()->sameSection(&Asm->MF->front())) {
-      const MCSymbol *BeginSectionLabel = StartLabel;
-
-      for (const MachineBasicBlock &MBB : *Asm->MF) {
-        if (MBB.isBeginSection() && &MBB != &Asm->MF->front())
-          BeginSectionLabel = MBB.getSymbol();
-
-        if (MBB.sameSection(Instr->getParent())) {
-          DebugLoc.emplace_back(BeginSectionLabel, EndLabel, Values);
-          break;
-        }
-        if (MBB.isEndSection())
-          DebugLoc.emplace_back(BeginSectionLabel, MBB.getEndSymbol(), Values);
-      }
-    } else {
-      DebugLoc.emplace_back(StartLabel, EndLabel, Values);
-    }
+    DebugLoc.emplace_back(StartLabel, EndLabel, Values);
 
     // Attempt to coalesce the ranges of two otherwise identical
     // DebugLocEntries.
@@ -1781,46 +1758,8 @@ bool DwarfDebug::buildLocationList(SmallVectorImpl<DebugLocEntry> &DebugLoc,
       DebugLoc.pop_back();
   }
 
-  if (!isSafeForSingleLocation ||
-      !validThroughout(LScopes, StartDebugMI, EndMI, getInstOrdering()))
-    return false;
-
-  if (DebugLoc.size() == 1)
-    return true;
-
-  if (!Asm->MF->hasBBSections())
-    return false;
-
-  // Check here to see if loclist can be merged into a single range. If not,
-  // we must keep the split loclists per section.  This does exactly what
-  // MergeRanges does without sections.  We don't actually merge the ranges
-  // as the split ranges must be kept intact if this cannot be collapsed
-  // into a single range.
-  const MachineBasicBlock *RangeMBB = nullptr;
-  if (DebugLoc[0].getBeginSym() == Asm->getFunctionBegin())
-    RangeMBB = &Asm->MF->front();
-  else
-    RangeMBB = Entries.begin()->getInstr()->getParent();
-  auto *CurEntry = DebugLoc.begin();
-  auto *NextEntry = std::next(CurEntry);
-  while (NextEntry != DebugLoc.end()) {
-    // Get the last machine basic block of this section.
-    while (!RangeMBB->isEndSection())
-      RangeMBB = RangeMBB->getNextNode();
-    if (!RangeMBB->getNextNode())
-      return false;
-    // CurEntry should end the current section and NextEntry should start
-    // the next section and the Values must match for these two ranges to be
-    // merged.
-    if (CurEntry->getEndSym() != RangeMBB->getEndSymbol() ||
-        NextEntry->getBeginSym() != RangeMBB->getNextNode()->getSymbol() ||
-        CurEntry->getValues() != NextEntry->getValues())
-      return false;
-    RangeMBB = RangeMBB->getNextNode();
-    CurEntry = NextEntry;
-    NextEntry = std::next(CurEntry);
-  }
-  return true;
+  return DebugLoc.size() == 1 && isSafeForSingleLocation &&
+         validThroughout(LScopes, StartDebugMI, EndMI, getInstOrdering());
 }
 
 DbgEntity *DwarfDebug::createConcreteEntity(DwarfCompileUnit &TheCU,