Fix performance bug in buildLocationList

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -1737,6 +1737,11 @@ void AsmPrinter::emitFunctionBody() {
   bool IsEHa = MMI->getModule()->getModuleFlag("eh-asynch");
 
   bool CanDoExtraAnalysis = ORE->allowExtraAnalysis(DEBUG_TYPE);
+  // Create a slot for the entry basic block section so that the section
+  // order is preserved when iterating over MBBSectionRanges.
+  if (!MF->empty())
+    MBBSectionRanges[MF->front().getSectionID()] = MBBSectionRange{CurrentFnBegin, nullptr};
+
   for (auto &MBB : *MF) {
     // Print a label for the basic block.
     emitBasicBlockStart(MBB);
@@ -2000,11 +2005,8 @@ void AsmPrinter::emitFunctionBody() {
   }
   for (auto &Handler : Handlers)
     Handler->markFunctionEnd();
-
-  assert(!MBBSectionRanges.contains(MF->front().getSectionID()) &&
-         "Overwrite section range");
-  MBBSectionRanges[MF->front().getSectionID()] =
-      MBBSectionRange{CurrentFnBegin, CurrentFnEnd};
+  // Update the end label of the entry block's section.
+  MBBSectionRanges[MF->front().getSectionID()].EndLabel = CurrentFnEnd;
 
   // Print out jump tables referenced by the function.
   emitJumpTableInfo();

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -34,6 +34,7 @@
 #include "llvm/DebugInfo/DWARF/DWARFDataExtractor.h"
 #include "llvm/DebugInfo/DWARF/DWARFExpression.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/Module.h"
@@ -1772,18 +1773,14 @@ bool DwarfDebug::buildLocationList(SmallVectorImpl<DebugLocEntry> &DebugLoc,
     // 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);
+      for (const auto &[MBBSectionId, MBBSectionRange] :
+           Asm->MBBSectionRanges) {
+        if (Instr->getParent()->getSectionID() == MBBSectionId) {
+          DebugLoc.emplace_back(MBBSectionRange.BeginLabel, EndLabel, Values);
           break;
         }
-        if (MBB.isEndSection())
-          DebugLoc.emplace_back(BeginSectionLabel, MBB.getEndSymbol(), Values);
+        DebugLoc.emplace_back(MBBSectionRange.BeginLabel,
+                              MBBSectionRange.EndLabel, Values);
       }
     } else {
       DebugLoc.emplace_back(StartLabel, EndLabel, Values);
@@ -1824,22 +1821,27 @@ bool DwarfDebug::buildLocationList(SmallVectorImpl<DebugLocEntry> &DebugLoc,
     RangeMBB = &Asm->MF->front();
   else
     RangeMBB = Entries.begin()->getInstr()->getParent();
+  auto RangeIt = Asm->MBBSectionRanges.find(RangeMBB->getSectionID());
+  assert(RangeIt != Asm->MBBSectionRanges.end() &&
+         "Range MBB not found in MBBSectionRanges!");
   auto *CurEntry = DebugLoc.begin();
   auto *NextEntry = std::next(CurEntry);
+  auto NextRangeIt = std::next(RangeIt);
   while (NextEntry != DebugLoc.end()) {
-    // Get the last machine basic block of this section.
-    while (!RangeMBB->isEndSection())
-      RangeMBB = RangeMBB->getNextNode();
-    if (!RangeMBB->getNextNode())
+    if (NextRangeIt == Asm->MBBSectionRanges.end())
       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() ||
+    // merged.  Do not match the section label end if it is the entry block
+    // section.  This is because the end label for the Debug Loc and the
+    // Function end label could be different.
+    if ((RangeIt->second.EndLabel != Asm->getFunctionEnd() &&
+         CurEntry->getEndSym() != RangeIt->second.EndLabel) ||
+        NextEntry->getBeginSym() != NextRangeIt->second.BeginLabel ||
         CurEntry->getValues() != NextEntry->getValues())
       return false;
-    RangeMBB = RangeMBB->getNextNode();
+    RangeIt = NextRangeIt;
+    NextRangeIt = std::next(RangeIt);
     CurEntry = NextEntry;
     NextEntry = std::next(CurEntry);
   }

llvm/test/DebugInfo/X86/basic-block-sections_1.ll

@@ -16,10 +16,10 @@
 ; NO-SECTIONS: DW_AT_high_pc [DW_FORM_data4] ({{.*}})
 ; BB-SECTIONS: DW_AT_low_pc [DW_FORM_addr] (0x0000000000000000)
 ; BB-SECTIONS-NEXT: DW_AT_ranges [DW_FORM_sec_offset]
+; BB-SECTIONS-NEXT: [{{.*}}) ".text.hot._Z3fooi"
 ; BB-SECTIONS-NEXT: [{{.*}}) ".text.hot._Z3fooi._Z3fooi.__part.1"
 ; BB-SECTIONS-NEXT: [{{.*}}) ".text.hot._Z3fooi._Z3fooi.__part.2"
 ; BB-SECTIONS-NEXT: [{{.*}}) ".text.hot._Z3fooi._Z3fooi.__part.3"
-; BB-SECTIONS-NEXT: [{{.*}}) ".text.hot._Z3fooi"
 ; BB-SECTIONS-ASM: _Z3fooi:
 ; BB-SECTIONS-ASM: .Ltmp{{[0-9]+}}:
 ; BB-SECTIONS-ASM-NEXT: .loc 1 2 9 prologue_end
@@ -36,14 +36,14 @@
 ; BB-SECTIONS-ASM: .size	_Z3fooi.__part.3, .LBB_END0_{{[0-9]+}}-_Z3fooi.__part.3
 ; BB-SECTIONS-ASM: .Lfunc_end0:
 ; BB-SECTIONS-ASM: .Ldebug_ranges0:
+; BB-SECTIONS-ASM-NEXT:	.quad	.Lfunc_begin0
+; BB-SECTIONS-ASM-NEXT:	.quad	.Lfunc_end0
 ; BB-SECTIONS-ASM-NEXT:	.quad	_Z3fooi.__part.1
 ; BB-SECTIONS-ASM-NEXT:	.quad	.LBB_END0_{{[0-9]+}}
 ; BB-SECTIONS-ASM-NEXT:	.quad	_Z3fooi.__part.2
 ; BB-SECTIONS-ASM-NEXT:	.quad	.LBB_END0_{{[0-9]+}}
 ; BB-SECTIONS-ASM-NEXT:	.quad	_Z3fooi.__part.3
 ; BB-SECTIONS-ASM-NEXT:	.quad	.LBB_END0_{{[0-9]+}}
-; BB-SECTIONS-ASM-NEXT:	.quad	.Lfunc_begin0
-; BB-SECTIONS-ASM-NEXT:	.quad	.Lfunc_end0
 ; BB-SECTIONS-ASM-NEXT:	.quad	0
 ; BB-SECTIONS-ASM-NEXT:	.quad	0
 ; BB-SECTIONS-LINE-TABLE:      0x0000000000000000 1 0 1 0 0 0 is_stmt