DebugInfo: Use base address selection entries for debug_loc

Unify the range and loc emission (for both DWARFv4 and DWARFv5 style lists) and take advantage of that unification to use strategic base addresses for loclists.

Differential Revision: https://reviews.llvm.org/D68620

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@374600 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -2293,14 +2293,121 @@ static MCSymbol *emitLoclistsTableHeader(AsmPrinter *Asm,
   return TableEnd;
 }
 
+template <typename Ranges, typename PayloadEmitter>
+static void emitRangeList(
+    DwarfDebug &DD, AsmPrinter *Asm, MCSymbol *Sym, const Ranges &R,
+    const DwarfCompileUnit &CU, unsigned BaseAddressx, unsigned OffsetPair,
+    unsigned StartxLength, unsigned EndOfList,
+    StringRef (*StringifyEnum)(unsigned),
+    bool ShouldUseBaseAddress,
+    PayloadEmitter EmitPayload) {
+
+  auto Size = Asm->MAI->getCodePointerSize();
+  bool UseDwarf5 = DD.getDwarfVersion() >= 5;
+
+  // Emit our symbol so we can find the beginning of the range.
+  Asm->OutStreamer->EmitLabel(Sym);
+
+  // Gather all the ranges that apply to the same section so they can share
+  // a base address entry.
+  MapVector<const MCSection *, std::vector<decltype(&*R.begin())>> SectionRanges;
+
+  for (const auto &Range : R)
+    SectionRanges[&Range.Begin->getSection()].push_back(&Range);
+
+  const MCSymbol *CUBase = CU.getBaseAddress();
+  bool BaseIsSet = false;
+  for (const auto &P : SectionRanges) {
+    auto *Base = CUBase;
+    if (!Base && ShouldUseBaseAddress) {
+      const MCSymbol *Begin = P.second.front()->Begin;
+      const MCSymbol *NewBase = DD.getSectionLabel(&Begin->getSection());
+      if (!UseDwarf5) {
+        Base = NewBase;
+        BaseIsSet = true;
+        Asm->OutStreamer->EmitIntValue(-1, Size);
+        Asm->OutStreamer->AddComment("  base address");
+        Asm->OutStreamer->EmitSymbolValue(Base, Size);
+      } else if (NewBase != Begin || P.second.size() > 1) {
+        // Only use a base address if
+        //  * the existing pool address doesn't match (NewBase != Begin)
+        //  * or, there's more than one entry to share the base address
+        Base = NewBase;
+        BaseIsSet = true;
+        Asm->OutStreamer->AddComment(StringifyEnum(BaseAddressx));
+        Asm->emitInt8(BaseAddressx);
+        Asm->OutStreamer->AddComment("  base address index");
+        Asm->EmitULEB128(DD.getAddressPool().getIndex(Base));
+      }
+    } else if (BaseIsSet && !UseDwarf5) {
+      BaseIsSet = false;
+      assert(!Base);
+      Asm->OutStreamer->EmitIntValue(-1, Size);
+      Asm->OutStreamer->EmitIntValue(0, Size);
+    }
+
+    for (const auto *RS : P.second) {
+      const MCSymbol *Begin = RS->Begin;
+      const MCSymbol *End = RS->End;
+      assert(Begin && "Range without a begin symbol?");
+      assert(End && "Range without an end symbol?");
+      if (Base) {
+        if (UseDwarf5) {
+          // Emit offset_pair when we have a base.
+          Asm->OutStreamer->AddComment(StringifyEnum(OffsetPair));
+          Asm->emitInt8(OffsetPair);
+          Asm->OutStreamer->AddComment("  starting offset");
+          Asm->EmitLabelDifferenceAsULEB128(Begin, Base);
+          Asm->OutStreamer->AddComment("  ending offset");
+          Asm->EmitLabelDifferenceAsULEB128(End, Base);
+        } else {
+          Asm->EmitLabelDifference(Begin, Base, Size);
+          Asm->EmitLabelDifference(End, Base, Size);
+        }
+      } else if (UseDwarf5) {
+        Asm->OutStreamer->AddComment(StringifyEnum(StartxLength));
+        Asm->emitInt8(StartxLength);
+        Asm->OutStreamer->AddComment("  start index");
+        Asm->EmitULEB128(DD.getAddressPool().getIndex(Begin));
+        Asm->OutStreamer->AddComment("  length");
+        Asm->EmitLabelDifferenceAsULEB128(End, Begin);
+      } else {
+        Asm->OutStreamer->EmitSymbolValue(Begin, Size);
+        Asm->OutStreamer->EmitSymbolValue(End, Size);
+      }
+      EmitPayload(*RS);
+    }
+  }
+
+  if (UseDwarf5) {
+    Asm->OutStreamer->AddComment(StringifyEnum(EndOfList));
+    Asm->emitInt8(EndOfList);
+  } else {
+    // Terminate the list with two 0 values.
+    Asm->OutStreamer->EmitIntValue(0, Size);
+    Asm->OutStreamer->EmitIntValue(0, Size);
+  }
+}
+
+static void emitLocList(DwarfDebug &DD, AsmPrinter *Asm, const DebugLocStream::List &List) {
+  emitRangeList(
+      DD, Asm, List.Label, DD.getDebugLocs().getEntries(List), *List.CU,
+      dwarf::DW_LLE_base_addressx, dwarf::DW_LLE_offset_pair,
+      dwarf::DW_LLE_startx_length, dwarf::DW_LLE_end_of_list,
+      llvm::dwarf::LocListEncodingString,
+      /* ShouldUseBaseAddress */ true,
+      [&](const DebugLocStream::Entry &E) {
+        DD.emitDebugLocEntryLocation(E, List.CU);
+      });
+}
+
 // Emit locations into the .debug_loc/.debug_rnglists section.
 void DwarfDebug::emitDebugLoc() {
   if (DebugLocs.getLists().empty())
     return;
 
-  bool IsLocLists = getDwarfVersion() >= 5;
   MCSymbol *TableEnd = nullptr;
-  if (IsLocLists) {
+  if (getDwarfVersion() >= 5) {
     Asm->OutStreamer->SwitchSection(
         Asm->getObjFileLowering().getDwarfLoclistsSection());
     TableEnd = emitLoclistsTableHeader(Asm, useSplitDwarf() ? SkeletonHolder
@@ -2310,63 +2417,8 @@ void DwarfDebug::emitDebugLoc() {
         Asm->getObjFileLowering().getDwarfLocSection());
   }
 
-  unsigned char Size = Asm->MAI->getCodePointerSize();
-  for (const auto &List : DebugLocs.getLists()) {
-    Asm->OutStreamer->EmitLabel(List.Label);
-
-    const DwarfCompileUnit *CU = List.CU;
-    const MCSymbol *Base = CU->getBaseAddress();
-    for (const auto &Entry : DebugLocs.getEntries(List)) {
-      if (Base) {
-        // Set up the range. This range is relative to the entry point of the
-        // compile unit. This is a hard coded 0 for low_pc when we're emitting
-        // ranges, or the DW_AT_low_pc on the compile unit otherwise.
-        if (IsLocLists) {
-          Asm->OutStreamer->AddComment("DW_LLE_offset_pair");
-          Asm->OutStreamer->EmitIntValue(dwarf::DW_LLE_offset_pair, 1);
-          Asm->OutStreamer->AddComment("  starting offset");
-          Asm->EmitLabelDifferenceAsULEB128(Entry.Begin, Base);
-          Asm->OutStreamer->AddComment("  ending offset");
-          Asm->EmitLabelDifferenceAsULEB128(Entry.End, Base);
-        } else {
-          Asm->EmitLabelDifference(Entry.Begin, Base, Size);
-          Asm->EmitLabelDifference(Entry.End, Base, Size);
-        }
-
-        emitDebugLocEntryLocation(Entry, CU);
-        continue;
-      }
-
-      // We have no base address.
-      if (IsLocLists) {
-        // TODO: Use DW_LLE_base_addressx + DW_LLE_offset_pair, or
-        // DW_LLE_startx_length in case if there is only a single range.
-        // That should reduce the size of the debug data emited.
-        // For now just use the DW_LLE_startx_length for all cases.
-        Asm->OutStreamer->AddComment("DW_LLE_startx_length");
-        Asm->emitInt8(dwarf::DW_LLE_startx_length);
-        Asm->OutStreamer->AddComment("  start idx");
-        Asm->EmitULEB128(AddrPool.getIndex(Entry.Begin));
-        Asm->OutStreamer->AddComment("  length");
-        Asm->EmitLabelDifferenceAsULEB128(Entry.End, Entry.Begin);
-      } else {
-        Asm->OutStreamer->EmitSymbolValue(Entry.Begin, Size);
-        Asm->OutStreamer->EmitSymbolValue(Entry.End, Size);
-      }
-
-      emitDebugLocEntryLocation(Entry, CU);
-    }
-
-    if (IsLocLists) {
-      // .debug_loclists section ends with DW_LLE_end_of_list.
-      Asm->OutStreamer->AddComment("DW_LLE_end_of_list");
-      Asm->OutStreamer->EmitIntValue(dwarf::DW_LLE_end_of_list, 1);
-    } else {
-      // Terminate the .debug_loc list with two 0 values.
-      Asm->OutStreamer->EmitIntValue(0, Size);
-      Asm->OutStreamer->EmitIntValue(0, Size);
-    }
-  }
+  for (const auto &List : DebugLocs.getLists())
+    emitLocList(*this, Asm, List);
 
   if (TableEnd)
     Asm->OutStreamer->EmitLabel(TableEnd);
@@ -2556,103 +2608,16 @@ void DwarfDebug::emitDebugARanges() {
   }
 }
 
-template <typename Ranges>
-static void emitRangeList(DwarfDebug &DD, AsmPrinter *Asm, MCSymbol *Sym,
-                          const Ranges &R, const DwarfCompileUnit &CU,
-                          unsigned BaseAddressx, unsigned OffsetPair,
-                          unsigned StartxLength, unsigned EndOfList,
-                          StringRef (*StringifyEnum)(unsigned)) {
-  auto DwarfVersion = DD.getDwarfVersion();
-  // Emit our symbol so we can find the beginning of the range.
-  Asm->OutStreamer->EmitLabel(Sym);
-  // Gather all the ranges that apply to the same section so they can share
-  // a base address entry.
-  MapVector<const MCSection *, std::vector<const RangeSpan *>> SectionRanges;
-  // Size for our labels.
-  auto Size = Asm->MAI->getCodePointerSize();
-
-  for (const RangeSpan &Range : R)
-    SectionRanges[&Range.Begin->getSection()].push_back(&Range);
-
-  const MCSymbol *CUBase = CU.getBaseAddress();
-  bool BaseIsSet = false;
-  for (const auto &P : SectionRanges) {
-    // Don't bother with a base address entry if there's only one range in
-    // this section in this range list - for example ranges for a CU will
-    // usually consist of single regions from each of many sections
-    // (-ffunction-sections, or just C++ inline functions) except under LTO
-    // or optnone where there may be holes in a single CU's section
-    // contributions.
-    auto *Base = CUBase;
-    if (!Base && (P.second.size() > 1 || DwarfVersion < 5) &&
-        (CU.getCUNode()->getRangesBaseAddress() || DwarfVersion >= 5)) {
-      BaseIsSet = true;
-      Base = DD.getSectionLabel(&P.second.front()->Begin->getSection());
-      if (DwarfVersion >= 5) {
-        Asm->OutStreamer->AddComment(StringifyEnum(BaseAddressx));
-        Asm->OutStreamer->EmitIntValue(BaseAddressx, 1);
-        Asm->OutStreamer->AddComment("  base address index");
-        Asm->EmitULEB128(DD.getAddressPool().getIndex(Base));
-      } else {
-        Asm->OutStreamer->EmitIntValue(-1, Size);
-        Asm->OutStreamer->AddComment("  base address");
-        Asm->OutStreamer->EmitSymbolValue(Base, Size);
-      }
-    } else if (BaseIsSet && DwarfVersion < 5) {
-      BaseIsSet = false;
-      assert(!Base);
-      Asm->OutStreamer->EmitIntValue(-1, Size);
-      Asm->OutStreamer->EmitIntValue(0, Size);
-    }
-
-    for (const auto *RS : P.second) {
-      const MCSymbol *Begin = RS->Begin;
-      const MCSymbol *End = RS->End;
-      assert(Begin && "Range without a begin symbol?");
-      assert(End && "Range without an end symbol?");
-      if (Base) {
-        if (DwarfVersion >= 5) {
-          // Emit DW_RLE_offset_pair when we have a base.
-          Asm->OutStreamer->AddComment(StringifyEnum(OffsetPair));
-          Asm->emitInt8(OffsetPair);
-          Asm->OutStreamer->AddComment("  starting offset");
-          Asm->EmitLabelDifferenceAsULEB128(Begin, Base);
-          Asm->OutStreamer->AddComment("  ending offset");
-          Asm->EmitLabelDifferenceAsULEB128(End, Base);
-        } else {
-          Asm->EmitLabelDifference(Begin, Base, Size);
-          Asm->EmitLabelDifference(End, Base, Size);
-        }
-      } else if (DwarfVersion >= 5) {
-        Asm->OutStreamer->AddComment(StringifyEnum(StartxLength));
-        Asm->emitInt8(StartxLength);
-        Asm->OutStreamer->AddComment("  start index");
-        Asm->EmitULEB128(DD.getAddressPool().getIndex(Begin));
-        Asm->OutStreamer->AddComment("  length");
-        Asm->EmitLabelDifferenceAsULEB128(End, Begin);
-      } else {
-        Asm->OutStreamer->EmitSymbolValue(Begin, Size);
-        Asm->OutStreamer->EmitSymbolValue(End, Size);
-      }
-    }
-  }
-  if (DwarfVersion >= 5) {
-    Asm->OutStreamer->AddComment(StringifyEnum(EndOfList));
-    Asm->emitInt8(EndOfList);
-  } else {
-    // Terminate the list with two 0 values.
-    Asm->OutStreamer->EmitIntValue(0, Size);
-    Asm->OutStreamer->EmitIntValue(0, Size);
-  }
-}
-
 /// Emit a single range list. We handle both DWARF v5 and earlier.
 static void emitRangeList(DwarfDebug &DD, AsmPrinter *Asm,
                           const RangeSpanList &List) {
   emitRangeList(DD, Asm, List.getSym(), List.getRanges(), List.getCU(),
                 dwarf::DW_RLE_base_addressx, dwarf::DW_RLE_offset_pair,
                 dwarf::DW_RLE_startx_length, dwarf::DW_RLE_end_of_list,
-                llvm::dwarf::RangeListEncodingString);
+                llvm::dwarf::RangeListEncodingString,
+                List.getCU().getCUNode()->getRangesBaseAddress() ||
+                    DD.getDwarfVersion() >= 5,
+                [](auto) {});
 }
 
 static void emitDebugRangesImpl(DwarfDebug &DD, AsmPrinter *Asm,

test/CodeGen/X86/debug-loclists.ll

@@ -1,144 +1,119 @@
-; RUN: llc -mtriple=x86_64-pc-linux -filetype=obj -o %t < %s
-; RUN: llvm-dwarfdump -v %t | FileCheck %s
-
-; CHECK:      0x00000033: DW_TAG_formal_parameter [3]
-; CHECK-NEXT:               DW_AT_location [DW_FORM_sec_offset]   (0x0000000c
-; CHECK-NEXT:                  [0x0000000000000000, 0x0000000000000004): DW_OP_breg5 RDI+0
-; CHECK-NEXT:                  [0x0000000000000004, 0x0000000000000012): DW_OP_breg3 RBX+0)
-; CHECK-NEXT:               DW_AT_name [DW_FORM_strx1]    (indexed (0000000e) string = "a")
-; CHECK-NEXT:               DW_AT_decl_file [DW_FORM_data1]       ("/home/folder{{\\|\/}}test.cc")
-; CHECK-NEXT:               DW_AT_decl_line [DW_FORM_data1]       (6)
-; CHECK-NEXT:               DW_AT_type [DW_FORM_ref4]     (cu + 0x0040 => {0x00000040} "A")
+; RUN: llc -mtriple=x86_64-pc-linux -filetype=obj -function-sections -o %t < %s
+; RUN: llvm-dwarfdump -v -debug-info -debug-loclists %t | FileCheck %s
+
+; CHECK:      DW_TAG_variable
+; FIXME: Use DW_FORM_loclistx to reduce relocations
+; CHECK-NEXT:   DW_AT_location [DW_FORM_sec_offset]   (0x0000000c
+; CHECK-NEXT:     [0x0000000000000000, 0x0000000000000003): DW_OP_consts +3, DW_OP_stack_value
+; CHECK-NEXT:     [0x0000000000000003, 0x0000000000000004): DW_OP_consts +4, DW_OP_stack_value)
+; CHECK-NEXT:   DW_AT_name {{.*}} "y"
+
+; CHECK:      DW_TAG_variable
+; FIXME: Use DW_FORM_loclistx to reduce relocations
+; CHECK-NEXT:   DW_AT_location [DW_FORM_sec_offset]   (0x0000001d
+; CHECK-NEXT:     Addr idx 0 (w/ length 3): DW_OP_consts +5, DW_OP_stack_value)
+; CHECK-NEXT:   DW_AT_name {{.*}} "x"
+
+; CHECK:      DW_TAG_variable
+; FIXME: Use DW_FORM_loclistx to reduce relocations
+; CHECK-NEXT:   DW_AT_location [DW_FORM_sec_offset]   (0x00000025
+; CHECK-NEXT:     [0x0000000000000003, 0x0000000000000004): DW_OP_reg0 RAX)
+; CHECK-NEXT:   DW_AT_name {{.*}} "r"
 
 ; CHECK:      .debug_loclists contents:
-; CHECK-NEXT: 0x00000000: locations list header: length = 0x00000015, version = 0x0005, addr_size = 0x08, seg_size = 0x00, offset_entry_count = 0x00000000
+; CHECK-NEXT: 0x00000000: locations list header: length = 0x00000029, version = 0x0005, addr_size = 0x08, seg_size = 0x00, offset_entry_count = 0x00000000
+
+; Don't use startx_length if there's more than one entry, because the shared
+; base address will be useful for both the range that does start at the start of
+; the function, and the one that doesn't.
+
 ; CHECK-NEXT: 0x0000000c:
-; CHECK-NEXT: DW_LLE_offset_pair(0x0000000000000000, 0x0000000000000004)
-; CHECK-NEXT:                => [0x0000000000000000, 0x0000000000000004): DW_OP_breg5 RDI+0
-; CHECK-NEXT: DW_LLE_offset_pair(0x0000000000000004, 0x0000000000000012)
-; CHECK-NEXT:                => [0x0000000000000004, 0x0000000000000012): DW_OP_breg3 RBX+0
-
-; There is no way to use llvm-dwarfdump atm (2018, october) to verify the DW_LLE_* codes emited,
-; because dumper is not yet implements that. Use asm code to do this check instead.
-;
-; RUN: llc -mtriple=x86_64-pc-linux -filetype=asm < %s -o - | FileCheck %s --check-prefix=ASM
-; ASM:      .section .debug_loclists,"",@progbits
-; ASM-NEXT: .long .Ldebug_loclist_table_end0-.Ldebug_loclist_table_start0 # Length
-; ASM-NEXT: .Ldebug_loclist_table_start0:
-; ASM-NEXT:  .short 5                              # Version
-; ASM-NEXT:  .byte 8                               # Address size
-; ASM-NEXT:  .byte 0                               # Segment selector size
-; ASM-NEXT:  .long 0                               # Offset entry count
-; ASM-NEXT: .Lloclists_table_base0:                
-; ASM-NEXT: .Ldebug_loc0:
-; ASM-NEXT:  .byte 4                               # DW_LLE_offset_pair
-; ASM-NEXT:  .uleb128 .Lfunc_begin0-.Lfunc_begin0  # starting offset
-; ASM-NEXT:  .uleb128 .Ltmp0-.Lfunc_begin0         # ending offset
-; ASM-NEXT:  .byte 2                               # Loc expr size
-; ASM-NEXT:  .byte 117                             # DW_OP_breg5
-; ASM-NEXT:  .byte 0                               # 0
-; ASM-NEXT:  .byte 4                               # DW_LLE_offset_pair
-; ASM-NEXT:  .uleb128 .Ltmp0-.Lfunc_begin0         # starting offset
-; ASM-NEXT:  .uleb128 .Ltmp1-.Lfunc_begin0         # ending offset
-; ASM-NEXT:  .byte 2                               # Loc expr size
-; ASM-NEXT:  .byte 115                             # DW_OP_breg3
-; ASM-NEXT:  .byte 0                               # 0
-; ASM-NEXT:  .byte 0                               # DW_LLE_end_of_list
-; ASM-NEXT: .Ldebug_loclist_table_end0:
-
-; ModuleID = 'test.cc'
-source_filename = "test.cc"
-target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
-target triple = "x86_64-unknown-linux-gnu"
-
-%struct.A = type { i32 (...)** }
-
-@_ZTV1A = dso_local unnamed_addr constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTI1A to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A3fooEv to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A3barEv to i8*)] }, align 8
-@_ZTVN10__cxxabiv117__class_type_infoE = external dso_local global i8*
-@_ZTS1A = dso_local constant [3 x i8] c"1A\00", align 1
-@_ZTI1A = dso_local constant { i8*, i8* } { i8* bitcast (i8** getelementptr inbounds (i8*, i8** @_ZTVN10__cxxabiv117__class_type_infoE, i64 2) to i8*), i8* getelementptr inbounds ([3 x i8], [3 x i8]* @_ZTS1A, i32 0, i32 0) }, align 8
-
-; Function Attrs: noinline optnone uwtable
-define dso_local void @_Z3baz1A(%struct.A* %a) #0 !dbg !7 {
-entry:
-  call void @llvm.dbg.declare(metadata %struct.A* %a, metadata !23, metadata !DIExpression()), !dbg !24
-  call void @_ZN1A3fooEv(%struct.A* %a), !dbg !25
-  call void @_ZN1A3barEv(%struct.A* %a), !dbg !26
-  ret void, !dbg !27
-}
+; CHECK-NEXT:             DW_LLE_base_addressx(0x0000000000000000)
+; CHECK-NEXT:             DW_LLE_offset_pair  (0x0000000000000000, 0x0000000000000003)
+; CHECK-NEXT:                              => [0x0000000000000000, 0x0000000000000003): DW_OP_consts +3, DW_OP_stack_value
+; CHECK-NEXT:             DW_LLE_offset_pair  (0x0000000000000003, 0x0000000000000004)
+; CHECK-NEXT:                              => [0x0000000000000003, 0x0000000000000004): DW_OP_consts +4, DW_OP_stack_value
+; CHECK-NEXT:             DW_LLE_end_of_list  ()
 
-; Function Attrs: nounwind readnone speculatable
-declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+; Show that startx_length can be used when the address range starts at the start of the function.
 
-; Function Attrs: noinline nounwind optnone uwtable
-define dso_local void @_ZN1A3fooEv(%struct.A* %this) unnamed_addr #2 align 2 !dbg !28 {
-entry:
-  %this.addr = alloca %struct.A*, align 8
-  store %struct.A* %this, %struct.A** %this.addr, align 8
-  call void @llvm.dbg.declare(metadata %struct.A** %this.addr, metadata !29, metadata !DIExpression()), !dbg !31
-  %this1 = load %struct.A*, %struct.A** %this.addr, align 8
-  ret void, !dbg !32
-}
+; CHECK:      0x0000001d:
+; CHECK-NEXT:             DW_LLE_startx_length(0x0000000000000000, 0x0000000000000003)
+; CHECK-NEXT:                              => Addr idx 0 (w/ length 3): DW_OP_consts +5, DW_OP_stack_value
+; CHECK-NEXT:             DW_LLE_end_of_list  ()
+
+; And use a base address when the range doesn't start at an existing/useful
+; address in the pool.
+
+; CHECK:      0x00000025:
+; CHECK-NEXT:             DW_LLE_base_addressx(0x0000000000000000)
+; CHECK-NEXT:             DW_LLE_offset_pair  (0x0000000000000003, 0x0000000000000004)
+; CHECK-NEXT:                              => [0x0000000000000003, 0x0000000000000004): DW_OP_reg0 RAX
+; CHECK-NEXT:             DW_LLE_end_of_list  ()
+
+; Built with clang -O3 -ffunction-sections from source:
+; 
+; int f1(int i, int j) {
+;   int x = 5;
+;   int y = 3;
+;   int r = i + j;
+;   int undef;
+;   x = undef;
+;   y = 4;
+;   return r;
+; }
+; void f2() {
+; }
 
-; Function Attrs: noinline nounwind optnone uwtable
-define dso_local void @_ZN1A3barEv(%struct.A* %this) unnamed_addr #2 align 2 !dbg !33 {
+; Function Attrs: norecurse nounwind readnone uwtable
+define dso_local i32 @_Z2f1ii(i32 %i, i32 %j) local_unnamed_addr !dbg !7 {
 entry:
-  %this.addr = alloca %struct.A*, align 8
-  store %struct.A* %this, %struct.A** %this.addr, align 8
-  call void @llvm.dbg.declare(metadata %struct.A** %this.addr, metadata !34, metadata !DIExpression()), !dbg !35
-  %this1 = load %struct.A*, %struct.A** %this.addr, align 8
-  ret void, !dbg !36
+  call void @llvm.dbg.value(metadata i32 %i, metadata !12, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i32 %j, metadata !13, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i32 5, metadata !14, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i32 3, metadata !15, metadata !DIExpression()), !dbg !18
+  %add = add nsw i32 %j, %i, !dbg !19
+  call void @llvm.dbg.value(metadata i32 %add, metadata !16, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i32 undef, metadata !14, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i32 4, metadata !15, metadata !DIExpression()), !dbg !18
+  ret i32 %add, !dbg !20
 }
 
-; Function Attrs: noinline norecurse nounwind optnone uwtable
-define dso_local i32 @main() #3 !dbg !37 {
+; Function Attrs: norecurse nounwind readnone uwtable
+define dso_local void @_Z2f2v() local_unnamed_addr !dbg !21 {
 entry:
-  %retval = alloca i32, align 4
-  store i32 0, i32* %retval, align 4
-  ret i32 0, !dbg !38
+  ret void, !dbg !24
 }
 
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata)
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!3, !4, !5}
 !llvm.ident = !{!6}
 
-!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 8.0.0 (trunk 344035)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
-!1 = !DIFile(filename: "test.cc", directory: "/home/folder", checksumkind: CSK_MD5, checksum: "e0f357ad6dcb791a774a0dae55baf5e7")
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 10.0.0 (trunk 374581) (llvm/trunk 374579)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "loc2.cpp", directory: "/usr/local/google/home/blaikie/dev/scratch", checksumkind: CSK_MD5, checksum: "91e0069c680e2a63f4f885ec93f5d07e")
 !2 = !{}
 !3 = !{i32 2, !"Dwarf Version", i32 5}
 !4 = !{i32 2, !"Debug Info Version", i32 3}
 !5 = !{i32 1, !"wchar_size", i32 4}
-!6 = !{!"clang version 8.0.0 (trunk 344035)"}
-!7 = distinct !DISubprogram(name: "baz", linkageName: "_Z3baz1A", scope: !1, file: !1, line: 6, type: !8, isLocal: false, isDefinition: true, scopeLine: 6, flags: DIFlagPrototyped, isOptimized: false, unit: !0, retainedNodes: !2)
+!6 = !{!"clang version 10.0.0 (trunk 374581) (llvm/trunk 374579)"}
+!7 = distinct !DISubprogram(name: "f1", linkageName: "_Z2f1ii", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
 !8 = !DISubroutineType(types: !9)
-!9 = !{null, !10}
-!10 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "A", file: !1, line: 1, size: 64, flags: DIFlagTypePassByReference, elements: !11, vtableHolder: !10, identifier: "_ZTS1A")
-!11 = !{!12, !18, !22}
-!12 = !DIDerivedType(tag: DW_TAG_member, name: "_vptr$A", scope: !1, file: !1, baseType: !13, size: 64, flags: DIFlagArtificial)
-!13 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !14, size: 64)
-!14 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "__vtbl_ptr_type", baseType: !15, size: 64)
-!15 = !DISubroutineType(types: !16)
-!16 = !{!17}
-!17 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
-!18 = !DISubprogram(name: "foo", linkageName: "_ZN1A3fooEv", scope: !10, file: !1, line: 2, type: !19, isLocal: false, isDefinition: false, scopeLine: 2, containingType: !10, virtuality: DW_VIRTUALITY_virtual, virtualIndex: 0, flags: DIFlagPrototyped, isOptimized: false)
-!19 = !DISubroutineType(types: !20)
-!20 = !{null, !21}
-!21 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !10, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
-!22 = !DISubprogram(name: "bar", linkageName: "_ZN1A3barEv", scope: !10, file: !1, line: 3, type: !19, isLocal: false, isDefinition: false, scopeLine: 3, containingType: !10, virtuality: DW_VIRTUALITY_virtual, virtualIndex: 1, flags: DIFlagPrototyped, isOptimized: false)
-!23 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 6, type: !10)
-!24 = !DILocation(line: 6, column: 19, scope: !7)
-!25 = !DILocation(line: 7, column: 6, scope: !7)
-!26 = !DILocation(line: 8, column: 6, scope: !7)
-!27 = !DILocation(line: 9, column: 1, scope: !7)
-!28 = distinct !DISubprogram(name: "foo", linkageName: "_ZN1A3fooEv", scope: !10, file: !1, line: 12, type: !19, isLocal: false, isDefinition: true, scopeLine: 12, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !18, retainedNodes: !2)
-!29 = !DILocalVariable(name: "this", arg: 1, scope: !28, type: !30, flags: DIFlagArtificial | DIFlagObjectPointer)
-!30 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !10, size: 64)
-!31 = !DILocation(line: 0, scope: !28)
-!32 = !DILocation(line: 12, column: 16, scope: !28)
-!33 = distinct !DISubprogram(name: "bar", linkageName: "_ZN1A3barEv", scope: !10, file: !1, line: 13, type: !19, isLocal: false, isDefinition: true, scopeLine: 13, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !22, retainedNodes: !2)
-!34 = !DILocalVariable(name: "this", arg: 1, scope: !33, type: !30, flags: DIFlagArtificial | DIFlagObjectPointer)
-!35 = !DILocation(line: 0, scope: !33)
-!36 = !DILocation(line: 13, column: 16, scope: !33)
-!37 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 15, type: !15, isLocal: false, isDefinition: true, scopeLine: 15, flags: DIFlagPrototyped, isOptimized: false, unit: !0, retainedNodes: !2)
-!38 = !DILocation(line: 16, column: 3, scope: !37)
+!9 = !{!10, !10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12, !13, !14, !15, !16, !17}
+!12 = !DILocalVariable(name: "i", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!13 = !DILocalVariable(name: "j", arg: 2, scope: !7, file: !1, line: 1, type: !10)
+!14 = !DILocalVariable(name: "x", scope: !7, file: !1, line: 2, type: !10)
+!15 = !DILocalVariable(name: "y", scope: !7, file: !1, line: 3, type: !10)
+!16 = !DILocalVariable(name: "r", scope: !7, file: !1, line: 4, type: !10)
+!17 = !DILocalVariable(name: "undef", scope: !7, file: !1, line: 5, type: !10)
+!18 = !DILocation(line: 0, scope: !7)
+!19 = !DILocation(line: 4, column: 13, scope: !7)
+!20 = !DILocation(line: 8, column: 3, scope: !7)
+!21 = distinct !DISubprogram(name: "f2", linkageName: "_Z2f2v", scope: !1, file: !1, line: 10, type: !22, scopeLine: 10, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!22 = !DISubroutineType(types: !23)
+!23 = !{null}
+!24 = !DILocation(line: 11, column: 1, scope: !21)

test/DebugInfo/X86/sret.ll

@@ -11,6 +11,7 @@
 ; CHECK: _ZN1B9AInstanceEv
 ; CHECK: DW_TAG_variable
 ; CHECK-NEXT:   DW_AT_location [DW_FORM_sec_offset] (0x00000000
+; CHECK-NEXT:     [0xffffffffffffffff, {{.*}}): {{$}}
 ; CHECK-NEXT:     [{{.*}}, {{.*}}): DW_OP_breg5 RDI+0
 ; CHECK-NEXT:     [{{.*}}, {{.*}}): DW_OP_breg6 RBP-24, DW_OP_deref)
 ; CHECK-NEXT:   DW_AT_name {{.*}}"a"