[DebugInfo][DWARF] Emit a single location instead of a location list

[Orlando]

Summary

for variables in nested scopes (including inlined functions) if there is a
single location which covers the entire scope and the scope is contained in a
single block.

With this change there are still scenarios where we can, but do not, emit a
single location for a variable. Still, this change significantly reduces the
size of .debug_loc for a clang-3.4 build and reduces the size of the .debug_info
section slightly too.

Compiler vs section size
*----------------------------------------------* 
|             | trunk     | patched   | change |
|             | (bytes)   | (bytes)   | (%)    |
|-------------|-----------|-----------|--------|
| .debug_loc  | 152128993 | 104924892 | -31.03 |
| .debug_info | 346249712 | 345249350 | -00.29 |
| file size   | 621497992 | 573304448 | -07.75 |
*----------------------------------------------*

As @jmorse mentioned here [0], it would be nice to not have to linearly scan,
but I don't think that can be avoided right now.

[0]: https://reviews.llvm.org/D77639#1969189

[aprantl]

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

1542

Does this do the right thing if the scope is "interrupted" by another scope within MBB?

[vsk]

This is really nice.

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

1542

Hm, are you describing a situation like this, where all the code is fit into one MBB?

{
  dbg_value "x"
  {
    dbg_value "y"
    ...
  }
}

If the inner scope is an inlined frame, I think it'd be ok for the location of 'x' to be valid throughout, since the debugger shouldn't consider 'x' in scope. If its a nested {} scope, 'x' should still be visible within it.

So I think this is ok. Might be good to add tests for this, though.

[aprantl]

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

1542

I was thinking about

MBB:
  insn 1 # scope A
  insn 2 # scope A
  insn 3 # completely unrelated scope B, instruction was moved here by a transformation
  insn 4 # scope A
...

[Orlando]

Thank you both for taking a look.

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

1542

I'm confident that we handle @vsk's example, but less sure about @aprantl's. I'll write up tests for both.

[Orlando]

I've updated the diff to include 'single-location-inlined-param.mir' and 'single-location-interrupted-scope.mir' which should cover both of those cases IIUC.

[vsk]

Thanks, I'm convinced this is doing the right thing now.

llvm/test/DebugInfo/X86/single-location-inlined-param.mir

31

Why are the DILocalVariables for 'local' and 'number' needed? I'm a bit concerned that their presence could make the check lines brittle.

llvm/test/DebugInfo/X86/single-location-interrupted-scope.mir

35

Wow, this is really neat. I see you've deleted the other DILocalVariables to simplify the check lines -- consider leaving a note about that here.

[Orlando]

+ Addressed your inline comments.

I wrote up an example of another improvement we could make here https://bugs.llvm.org/show_bug.cgi?id=45889.

[vsk]

Thanks, lgtm. Could you wait for @aprantl to double-check this as well?

[aprantl]

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

1542

I'm confident that we handle @vsk's example, but less sure about @aprantl's. I'll write up tests for both.

What came out of that investigation?

[Orlando]

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

1542

Ah, sorry, I replied to this with a non-inline comment. I added two more tests, 'single-location-inlined-param.mir' and 'single-location-interrupted-scope.mir', which should cover both of these situations.

[Orlando]

Thank you both, and @jmorse for doing a lot of the heavy lifting on this before I got to it.

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

static bool validThroughout(LexicalScopes &LScopes,
   auto *LScope = LScopes.findLexicalScope(DL);
   // Scope doesn't exist; this is a dead DBG_VALUE.
   if (!LScope)
     return false;
   auto &LSRange = LScope->getRanges();
   if (LSRange.size() == 0)
     return false;
 
-  // If this range is neither open ended nor a constant, then it is not a
-  // candidate for being validThroughout.
-  if (RangeEnd && !DbgValue->getOperand(0).isImm())
-    return false;
 
   // Determine if the DBG_VALUE is valid at the beginning of its lexical block.
   const MachineInstr *LScopeBegin = LSRange.front().first;
   // Early exit if the lexical scope begins outside of the current block.
   if (LScopeBegin->getParent() != MBB)
     return false;
 
   // If there are instructions belonging to our scope in another block, and
static bool validThroughout(LexicalScopes &LScopes,
 
   // Single, constant DBG_VALUEs in the prologue are promoted to be live
   // throughout the function. This is a hack, presumably for DWARF v2 and not
   // necessarily correct. It would be much better to use a dbg.declare instead
   // if we know the constant is live throughout the scope.
   if (DbgValue->getOperand(0).isImm() && MBB->pred_empty())
     return true;
 
+  // Now check for situations where an "open-ended" DBG_VALUE isn't enough to
+  // determine eligibility for a single location, e.g. nested scopes, inlined
+  // functions.
+  // FIXME: For now we just handle a simple (but common) case where the scope
+  // is contained in MBB. We could be smarter here.
+  //
+  // At this point we know that our scope ends in MBB. So, if RangeEnd exists
+  // outside of the block we can ignore it; the location is just leaking outside
+  // its scope.
+  assert(LScopeEnd->getParent() == MBB && "Scope ends outside MBB");
+  if (RangeEnd->getParent() != DbgValue->getParent())
+    return true;
+
+  // The location range and variable's enclosing scope are both contained within
+  // MBB, test if location terminates before end of scope.
+  for (auto I = RangeEnd->getIterator(); I != MBB->end(); ++I)
+    if (&*I == LScopeEnd)
       return false;
+
+  // There's a single location which starts at the scope start, and ends at or
+  // after the scope end.
+  return true;
 }
 
 /// Build the location list for all DBG_VALUEs in the function that
 /// describe the same variable. The resulting DebugLocEntries will have
 /// strict monotonically increasing begin addresses and will never
 /// overlap. If the resulting list has only one entry that is valid
 /// throughout variable's scope return true.
 //

llvm/test/DebugInfo/X86/single-location-inlined-param.mir

+# RUN: llc -start-after=livedebugvalues --filetype=obj %s -o - \
+# RUN:     | llvm-dwarfdump -v -name=param - | FileCheck %s
+#
+# Generated with opt -sroa -inline, llc -stop-after=livedebugvalues, with some
+# metadata removed by hand.
+#
+# int glob;
+# __attribute__((always_inline))
+# static void inline_me(int param) {
+#   {
+#     int local = param;
+#     glob = local;
+#   }
+# }
+# int fun(int number) {
+#   inline_me(number);
+#   if (number)
+#     return 0;
+#   return 1;
+# }
+#
+# The inlined parameter 'param' is available for the entirety of its enclosing
+# scope. We expect to see a single location entry despite the fact that the
+# final instruction in that scope belongs to a dominated scope.
+#
+# Except for 'param', all DILocalVariable metadata has been removed.
+#
+# Ignore first entry (abstract), we want to look at the concrete instance.
+# CHECK:       DW_TAG_formal_parameter [
+# CHECK:       DW_TAG_formal_parameter [
+# CHECK-NEXT:    DW_AT_location [DW_FORM_exprloc] (DW_OP_reg5 RDI)
+# CHECK-NEXT:    DW_AT_abstract_origin {{.*}} "param"
+
+--- |
+  target triple = "x86_64-unknown-linux-gnu"
+
+  @glob = dso_local global i32 0, align 4, !dbg !0
+  declare void @llvm.dbg.declare(metadata, metadata, metadata)
+  declare void @llvm.dbg.value(metadata, metadata, metadata)
+  define dso_local i32 @fun(i32 %number) !dbg !11 {
+  entry:
+    call void @llvm.dbg.value(metadata i32 %number, metadata !17, metadata !DIExpression()), !dbg !24
+    store i32 %number, i32* @glob, align 4, !dbg !27
+    %tobool = icmp ne i32 %number, 0, !dbg !32
+    br i1 %tobool, label %return, label %if.end, !dbg !34
+
+  if.end:                                           ; preds = %entry
+    br label %return, !dbg !35
+
+  return:                                           ; preds = %entry, %if.end
+    %retval.0 = phi i32 [ 1, %if.end ], [ 0, %entry ], !dbg !16
+    ret i32 %retval.0, !dbg !36
+  }
+
+  !llvm.dbg.cu = !{!2}
+  !llvm.module.flags = !{!7, !8, !9}
+  !llvm.ident = !{!10}
+
+  !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+  !1 = distinct !DIGlobalVariable(name: "glob", scope: !2, file: !3, line: 1, type: !6, isLocal: false, isDefinition: true)
+  !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 11.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, splitDebugInlining: false, nameTableKind: None)
+  !3 = !DIFile(filename: "test.c", directory: "/")
+  !4 = !{}
+  !5 = !{!0}
+  !6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !7 = !{i32 7, !"Dwarf Version", i32 4}
+  !8 = !{i32 2, !"Debug Info Version", i32 3}
+  !9 = !{i32 1, !"wchar_size", i32 4}
+  !10 = !{!"clang version 11.0.0"}
+  !11 = distinct !DISubprogram(name: "fun", scope: !3, file: !3, line: 9, type: !12, scopeLine: 9, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !14)
+  !12 = !DISubroutineType(types: !13)
+  !13 = !{!6, !6}
+  !14 = !{}
+  !16 = !DILocation(line: 0, scope: !11)
+  !17 = !DILocalVariable(name: "param", arg: 1, scope: !18, file: !3, line: 3, type: !6)
+  !18 = distinct !DISubprogram(name: "inline_me", scope: !3, file: !3, line: 3, type: !19, scopeLine: 3, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !21)
+  !19 = !DISubroutineType(types: !20)
+  !20 = !{null, !6}
+  !21 = !{!17}
+  !23 = distinct !DILexicalBlock(scope: !18, file: !3, line: 4, column: 3)
+  !24 = !DILocation(line: 0, scope: !18, inlinedAt: !25)
+  !25 = distinct !DILocation(line: 10, column: 3, scope: !11)
+  !26 = !DILocation(line: 0, scope: !23, inlinedAt: !25)
+  !27 = !DILocation(line: 6, column: 10, scope: !23, inlinedAt: !25)
+  !32 = !DILocation(line: 11, column: 7, scope: !33)
+  !33 = distinct !DILexicalBlock(scope: !11, file: !3, line: 11, column: 7)
+  !34 = !DILocation(line: 11, column: 7, scope: !11)
+  !35 = !DILocation(line: 13, column: 3, scope: !11)
+  !36 = !DILocation(line: 14, column: 1, scope: !11)
+
+...
+---
+name:            fun
+body:             |
+  bb.0.entry:
+    successors: %bb.2(0x50000000), %bb.1(0x30000000)
+    liveins: $edi
+
+    DBG_VALUE $edi, $noreg, !17, !DIExpression(), debug-location !24
+    MOV32mr $rip, 1, $noreg, @glob, $noreg, renamable $edi, debug-location !27 :: (store 4 into @glob)
+    renamable $eax = XOR32rr undef $eax, undef $eax, implicit-def dead $eflags
+    TEST32rr killed renamable $edi, renamable $edi, implicit-def $eflags, debug-location !32
+    JCC_1 %bb.1, 4, implicit $eflags, debug-location !34
+
+  bb.2.return:
+    liveins: $eax
+
+    RETQ $eax, debug-location !36
+
+  bb.1.if.end:
+    renamable $eax = MOV32ri 1
+    RETQ $eax, debug-location !36
+
+...

llvm/test/DebugInfo/X86/single-location-interrupted-scope.mir

+# RUN: llc -start-after=livedebugvalues --filetype=obj %s -o - \
+# RUN:     | llvm-dwarfdump -v -name=parama - | FileCheck %s
+#
+# Generated with -O2, llc -stop-after=livedebugvalues, with IR modified from
+# this source:
+#
+# int globa, globb;
+# void ext();
+# static void set(int parama, int paramb) {
+#   globa = parama;
+#   globb = paramb;
+# }
+# void funone(int one, int two) {
+#   two = two + one;
+#   // 'two = ...' sunk between the inlined assignments to globa and globa.
+#   set(one, two);
+#   if (two > 0)
+#     return ext();
+# }
+# void funtwo(int one, int two) {
+#   two = one + two;
+#   // 'two = ...' sunk between the inlined assignments to globa and globa,
+#   // and rdi is clobbered by the sunk 'two = ...'.
+#   set(one, two);
+#   if (one < two)
+#     return ext();
+# }
+#
+# Check that the 'parama' is available for the entire inlined scope in funone,
+# and that it is unavailable in the second DW_AT_ranges segment of the inlined
+# scope in funtwo. In both cases the inlined scope 'set' is intrerrupted by an
+# instruction from the calling function.
+#
+# Except for 'parama', all DILocalVariable metadata has been removed.
+#
+# Ignore first entry (abstract), we want to look at the concrete instances.
+# CHECK:       DW_TAG_formal_parameter [
+# CHECK:       DW_TAG_formal_parameter [
+# CHECK-NEXT:    DW_AT_location [DW_FORM_exprloc] (DW_OP_reg5 RDI)
+# CHECK-NEXT:    DW_AT_abstract_origin {{.*}} "parama"
+# CHECK:       DW_TAG_formal_parameter [
+# CHECK-NEXT:    DW_AT_location [DW_FORM_sec_offset]
+# CHECK-NEXT:      [0x{{[0-9a-b]+}}, 0x{{[0-9a-b]+}})
+# CHECK-NEXT:    DW_AT_abstract_origin {{.*}} "parama"
+
+--- |
+  target triple = "x86_64-unknown-linux-gnu"
+
+  @globa = dso_local local_unnamed_addr global i32 0, align 4, !dbg !0
+  @globb = dso_local local_unnamed_addr global i32 0, align 4, !dbg !10
+
+  declare !dbg !6 dso_local void @ext(...) local_unnamed_addr
+  declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+  define dso_local void @funone(i32 %one, i32 %two) local_unnamed_addr !dbg !17 {
+  entry:
+    call void @llvm.dbg.value(metadata i32 %one, metadata !20, metadata !DIExpression()), !dbg !23
+    store i32 %one, i32* @globa, align 4, !dbg !25
+    %add = add nsw i32 %two, %one, !dbg !30
+    store i32 %add, i32* @globb, align 4, !dbg !31
+    %cmp = icmp sgt i32 %add, 0, !dbg !32
+    br i1 %cmp, label %if.then, label %if.end, !dbg !34
+
+  if.then:                                          ; preds = %entry
+    tail call void (...) @ext(), !dbg !35
+    ret void, !dbg !36
+
+  if.end:                                           ; preds = %entry
+    ret void, !dbg !36
+  }
+
+  define dso_local void @funtwo(i32 %one, i32 %two) local_unnamed_addr !dbg !37 {
+  entry:
+    call void @llvm.dbg.value(metadata i32 %one, metadata !20, metadata !DIExpression()), !dbg !41
+    store i32 %one, i32* @globa, align 4, !dbg !43
+    %add = add nsw i32 %two, %one, !dbg !44
+    store i32 %add, i32* @globb, align 4, !dbg !45
+    %cmp = icmp sgt i32 %two, 0, !dbg !46
+    br i1 %cmp, label %if.then, label %if.end, !dbg !48
+
+  if.then:                                          ; preds = %entry
+    tail call void (...) @ext(), !dbg !49
+    ret void, !dbg !50
+
+  if.end:                                           ; preds = %entry
+    ret void, !dbg !50
+  }
+
+  !llvm.dbg.cu = !{!2}
+  !llvm.module.flags = !{!13, !14, !15}
+  !llvm.ident = !{!16}
+
+  !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+  !1 = distinct !DIGlobalVariable(name: "globa", scope: !2, file: !3, line: 16, type: !12, isLocal: false, isDefinition: true)
+  !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 11.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, retainedTypes: !5, globals: !9, splitDebugInlining: false, nameTableKind: None)
+  !3 = !DIFile(filename: "test.c", directory: "/")
+  !4 = !{}
+  !5 = !{!6}
+  !6 = !DISubprogram(name: "ext", scope: !3, file: !3, line: 17, type: !7, spFlags: DISPFlagOptimized, retainedNodes: !4)
+  !7 = !DISubroutineType(types: !8)
+  !8 = !{null, null}
+  !9 = !{!0, !10}
+  !10 = !DIGlobalVariableExpression(var: !11, expr: !DIExpression())
+  !11 = distinct !DIGlobalVariable(name: "globb", scope: !2, file: !3, line: 16, type: !12, isLocal: false, isDefinition: true)
+  !12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !13 = !{i32 7, !"Dwarf Version", i32 4}
+  !14 = !{i32 2, !"Debug Info Version", i32 3}
+  !15 = !{i32 1, !"wchar_size", i32 4}
+  !16 = !{!"clang version 11.0.0"}
+  !17 = distinct !DISubprogram(name: "funone", scope: !3, file: !3, line: 22, type: !18, scopeLine: 22, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !4)
+  !18 = !DISubroutineType(types: !19)
+  !19 = !{null, !12, !12}
+  !20 = !DILocalVariable(name: "parama", arg: 1, scope: !21, file: !3, line: 18, type: !12)
+  !21 = distinct !DISubprogram(name: "set", scope: !3, file: !3, line: 18, type: !18, scopeLine: 18, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !22)
+  !22 = !{!20}
+  !23 = !DILocation(line: 0, scope: !21, inlinedAt: !24)
+  !24 = distinct !DILocation(line: 24, column: 3, scope: !17)
+  !25 = !DILocation(line: 19, column: 9, scope: !21, inlinedAt: !24)
+  !30 = !DILocation(line: 23, column: 13, scope: !17)
+  !31 = !DILocation(line: 20, column: 9, scope: !21, inlinedAt: !24)
+  !32 = !DILocation(line: 25, column: 11, scope: !33)
+  !33 = distinct !DILexicalBlock(scope: !17, file: !3, line: 25, column: 7)
+  !34 = !DILocation(line: 25, column: 7, scope: !17)
+  !35 = !DILocation(line: 26, column: 12, scope: !33)
+  !36 = !DILocation(line: 27, column: 1, scope: !17)
+  !37 = distinct !DISubprogram(name: "funtwo", scope: !3, file: !3, line: 28, type: !18, scopeLine: 28, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !38)
+  !38 = !{}
+  !41 = !DILocation(line: 0, scope: !21, inlinedAt: !42)
+  !42 = distinct !DILocation(line: 30, column: 3, scope: !37)
+  !43 = !DILocation(line: 19, column: 9, scope: !21, inlinedAt: !42)
+  !44 = !DILocation(line: 29, column: 13, scope: !37)
+  !45 = !DILocation(line: 20, column: 9, scope: !21, inlinedAt: !42)
+  !46 = !DILocation(line: 31, column: 11, scope: !47)
+  !47 = distinct !DILexicalBlock(scope: !37, file: !3, line: 31, column: 7)
+  !48 = !DILocation(line: 31, column: 7, scope: !37)
+  !49 = !DILocation(line: 32, column: 12, scope: !47)
+  !50 = !DILocation(line: 33, column: 1, scope: !37)
+
+...
+---
+name:            funone
+body:             |
+  bb.0.entry:
+    successors: %bb.2(0x50000000), %bb.1(0x30000000)
+    liveins: $edi, $esi
+
+    DBG_VALUE $edi, $noreg, !20, !DIExpression(), debug-location !23
+    MOV32mr $rip, 1, $noreg, @globa, $noreg, renamable $edi, debug-location !25 :: (store 4 into @globa)
+    renamable $esi = ADD32rr killed renamable $esi, killed renamable $edi, implicit-def $eflags, debug-location !32
+    MOV32mr $rip, 1, $noreg, @globb, $noreg, killed renamable $esi, debug-location !31 :: (store 4 into @globb)
+    JCC_1 %bb.1, 14, implicit $eflags, debug-location !34
+
+  bb.2.if.then:
+    dead $eax = XOR32rr undef $eax, undef $eax, implicit-def dead $eflags, implicit-def $al, debug-location !35
+    TAILJMPd64 @ext, csr_64, implicit $rsp, implicit $ssp, implicit $rsp, implicit $ssp, implicit killed $al, debug-location !35
+
+  bb.1.if.end:
+    RETQ debug-location !36
+
+...
+---
+name:            funtwo
+body:             |
+  bb.0.entry:
+    successors: %bb.2(0x50000000), %bb.1(0x30000000)
+    liveins: $edi, $esi
+
+    DBG_VALUE $edi, $noreg, !20, !DIExpression(), debug-location !41
+    MOV32mr $rip, 1, $noreg, @globa, $noreg, renamable $edi, debug-location !43 :: (store 4 into @globa)
+    renamable $edi = nsw ADD32rr killed renamable $edi, renamable $esi, implicit-def dead $eflags, debug-location !44
+    MOV32mr $rip, 1, $noreg, @globb, $noreg, killed renamable $edi, debug-location !45 :: (store 4 into @globb)
+    TEST32rr killed renamable $esi, renamable $esi, implicit-def $eflags, debug-location !46
+    JCC_1 %bb.1, 14, implicit $eflags, debug-location !48
+
+  bb.2.if.then:
+    dead $eax = XOR32rr undef $eax, undef $eax, implicit-def dead $eflags, implicit-def $al, debug-location !49
+    TAILJMPd64 @ext, csr_64, implicit $rsp, implicit $ssp, implicit $rsp, implicit $ssp, implicit killed $al, debug-location !49
+
+  bb.1.if.end:
+    RETQ debug-location !50
+
+...

llvm/test/DebugInfo/X86/single-location.mir

+# RUN: llc -start-after=livedebugvalues --filetype=obj %s -o - \
+# RUN:     | llvm-dwarfdump -v - | FileCheck %s
+#
+# Generated at -O2, stopped after livedebugvalues, with some metadata removed
+# by hand:
+# int global;
+# void ext();
+# void fun(int p) {
+#   {
+#     int local = p;
+#     global = local;
+#   }
+#   ext();
+# }
+#
+# The variable 'local' is available for the entirety of its enclosing scope so
+# we expect to see a single location entry.
+#
+# Except for 'local', all DILocalVariable metadata has been removed.
+#
+# CHECK:     DW_TAG_lexical_block [
+# CHECK:       DW_TAG_variable
+# CHECK-NEXT:    DW_AT_location [DW_FORM_exprloc] (DW_OP_reg5 RDI)
+# CHECK-NEXT:    DW_AT_name {{.*}} = "local"
+
+--- |
+  target triple = "x86_64-unknown-linux-gnu"
+  @global = dso_local local_unnamed_addr global i32 0, align 4, !dbg !0
+  define dso_local void @fun(i32 %p) local_unnamed_addr !dbg !15 {
+  entry:
+    call void @llvm.dbg.value(metadata i32 %p, metadata !20, metadata !DIExpression()), !dbg !23
+    store i32 %p, i32* @global, align 4, !dbg !24
+    tail call void (...) @ext(), !dbg !29
+    ret void, !dbg !30
+  }
+
+  declare !dbg !6 dso_local void @ext(...) local_unnamed_addr
+  declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+  !llvm.dbg.cu = !{!2}
+  !llvm.module.flags = !{!11, !12, !13}
+  !llvm.ident = !{!14}
+
+  !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+  !1 = distinct !DIGlobalVariable(name: "global", scope: !2, file: !3, line: 1, type: !10, isLocal: false, isDefinition: true)
+  !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 11.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, retainedTypes: !5, globals: !9, splitDebugInlining: false, nameTableKind: None)
+  !3 = !DIFile(filename: "test.c", directory: "/")
+  !4 = !{}
+  !5 = !{!6}
+  !6 = !DISubprogram(name: "ext", scope: !3, file: !3, line: 2, type: !7, spFlags: DISPFlagOptimized, retainedNodes: !4)
+  !7 = !DISubroutineType(types: !8)
+  !8 = !{null, null}
+  !9 = !{!0}
+  !10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !11 = !{i32 7, !"Dwarf Version", i32 4}
+  !12 = !{i32 2, !"Debug Info Version", i32 3}
+  !13 = !{i32 1, !"wchar_size", i32 4}
+  !14 = !{!"clang version 11.0.0"}
+  !15 = distinct !DISubprogram(name: "fun", scope: !3, file: !3, line: 3, type: !16, scopeLine: 3, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !18)
+  !16 = !DISubroutineType(types: !17)
+  !17 = !{null, !10}
+  !18 = !{!20}
+  !20 = !DILocalVariable(name: "local", scope: !21, file: !3, line: 5, type: !10)
+  !21 = distinct !DILexicalBlock(scope: !15, file: !3, line: 4, column: 3)
+  !22 = !DILocation(line: 0, scope: !15)
+  !23 = !DILocation(line: 0, scope: !21)
+  !24 = !DILocation(line: 6, column: 12, scope: !21)
+  !29 = !DILocation(line: 8, column: 3, scope: !15)
+  !30 = !DILocation(line: 9, column: 1, scope: !15)
+
+...
+---
+name:            fun
+body:             |
+  bb.0.entry:
+    liveins: $edi
+
+    DBG_VALUE $edi, $noreg, !20, !DIExpression(), debug-location !23
+    MOV32mr $rip, 1, $noreg, @global, $noreg, killed renamable $edi, debug-location !24 :: (store 4 into @global)
+    dead $eax = XOR32rr undef $eax, undef $eax, implicit-def dead $eflags, implicit-def $al, debug-location !29
+    TAILJMPd64 @ext, csr_64, implicit $rsp, implicit $ssp, implicit $rsp, implicit $ssp, implicit killed $al, debug-location !29
+...