[DebugInfo] Fix assertion for extern void type

Commit d77ae1552fc2 ("[DebugInfo] Support to emit debugInfo
for extern variables") added support to emit debuginfo
for extern variables. Currently, only BPF target enables to
emit debuginfo for extern variables.

But if the extern variable has "void" type, the compilation will
fail.

  -bash-4.4$ cat t.c
  extern void bla;
  void *test() {
    void *x = &bla;
    return x;
  }
  -bash-4.4$ clang -target bpf -g -O2 -S t.c
  missing global variable type
  !1 = distinct !DIGlobalVariable(name: "bla", scope: !2, file: !3, line: 1,
                                  isLocal: false, isDefinition: false)
  ...
  fatal error: error in backend: Broken module found, compilation aborted!
  PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace,
      preprocessed source, and associated run script.
  Stack dump:
  ...

The IR requires a DIGlobalVariable must have a valid type and the
"void" type does not generate any type, hence the above fatal error.

Note that if the extern variable is defined as "const void", the
compilation will succeed.

-bash-4.4$ cat t.c
extern const void bla;
const void *test() {
  const void *x = &bla;
  return x;
}
-bash-4.4$ clang -target bpf -g -O2 -S t.c
-bash-4.4$ cat t.ll
...
!1 = distinct !DIGlobalVariable(name: "bla", scope: !2, file: !3, line: 1,
                                type: !6, isLocal: false, isDefinition: false)
!6 = !DIDerivedType(tag: DW_TAG_const_type, baseType: null)
...

Since currently, "const void extern_var" is supported by the
debug info, it is natural that "void extern_var" should also
be supported. This patch disabled assertion of "void extern_var"
in IR verifier and add proper guarding when emiting potential
null debug info type to dwarf types.

Differential Revision: https://reviews.llvm.org/D81131

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index 8d6849b..8fdc020 100644 (file)
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -156,7 +156,8 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
     DeclContext = GV->getScope();
     // Add name and type.
     addString(*VariableDIE, dwarf::DW_AT_name, GV->getDisplayName());
-    addType(*VariableDIE, GTy);
+    if (GTy)
+      addType(*VariableDIE, GTy);
 
     // Add scoping info.
     if (!GV->isLocalToUnit())

diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 7b13b7f..88c4116 100644 (file)
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -1278,7 +1278,9 @@ void Verifier::visitDIGlobalVariable(const DIGlobalVariable &N) {
 
   AssertDI(N.getTag() == dwarf::DW_TAG_variable, "invalid tag", &N);
   AssertDI(isType(N.getRawType()), "invalid type ref", &N, N.getRawType());
-  AssertDI(N.getType(), "missing global variable type", &N);
+  // Assert only if the global variable is not an extern
+  if (N.isDefinition())
+    AssertDI(N.getType(), "missing global variable type", &N);
   if (auto *Member = N.getRawStaticDataMemberDeclaration()) {
     AssertDI(isa<DIDerivedType>(Member),
              "invalid static data member declaration", &N, Member);

diff --git a/llvm/test/DebugInfo/BPF/extern-void.ll b/llvm/test/DebugInfo/BPF/extern-void.ll
new file mode 100644 (file)
index 0000000..3bf8e27
--- /dev/null
+++ b/llvm/test/DebugInfo/BPF/extern-void.ll
@@ -0,0 +1,81 @@
+; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+; RUN: llc -march=bpfeb -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+;
+; Source code:
+;   extern void bla1;
+;   void *test1() {
+;     void *x = &bla1;
+;     return x;
+;   }
+;
+;   extern const void bla2;
+;   const void *test2() {
+;     const void *x = &bla2;
+;     return x;
+;   }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm t.c
+
+@bla1 = external dso_local global i8, align 1, !dbg !0
+@bla2 = external dso_local constant i8, align 1, !dbg !6
+
+; Function Attrs: norecurse nounwind readnone
+define dso_local nonnull i8* @test1() local_unnamed_addr #0 !dbg !13 {
+entry:
+  call void @llvm.dbg.value(metadata i8* @bla1, metadata !18, metadata !DIExpression()), !dbg !19
+  ret i8* @bla1, !dbg !20
+}
+
+; Function Attrs: norecurse nounwind readnone
+define dso_local nonnull i8* @test2() local_unnamed_addr #0 !dbg !21 {
+entry:
+  call void @llvm.dbg.value(metadata i8* @bla2, metadata !26, metadata !DIExpression()), !dbg !27
+  ret i8* @bla2, !dbg !28
+}
+
+; CHECK:        .quad bla1
+; CHECK-NEXT:   DW_TAG_variable
+;
+; CHECK:        .quad   bla2
+; CHECK-NEXT:   DW_TAG_const_type
+; CHECK-NEXT:   DW_TAG_subprogram
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { norecurse nounwind readnone "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!9, !10, !11}
+!llvm.ident = !{!12}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "bla1", scope: !2, file: !3, line: 1, isLocal: false, isDefinition: false)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 11.0.0 (https://github.com/llvm/llvm-project.git 8a8c6913a931e8bbd119012f4badd81155a0f48a)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "t.c", directory: "/home/yhs/tmp3")
+!4 = !{}
+!5 = !{!0, !6}
+!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = distinct !DIGlobalVariable(name: "bla2", scope: !2, file: !3, line: 7, type: !8, isLocal: false, isDefinition: false)
+!8 = !DIDerivedType(tag: DW_TAG_const_type, baseType: null)
+!9 = !{i32 7, !"Dwarf Version", i32 4}
+!10 = !{i32 2, !"Debug Info Version", i32 3}
+!11 = !{i32 1, !"wchar_size", i32 4}
+!12 = !{!"clang version 11.0.0 (https://github.com/llvm/llvm-project.git 8a8c6913a931e8bbd119012f4badd81155a0f48a)"}
+!13 = distinct !DISubprogram(name: "test1", scope: !3, file: !3, line: 2, type: !14, scopeLine: 2, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !17)
+!14 = !DISubroutineType(types: !15)
+!15 = !{!16}
+!16 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+!17 = !{!18}
+!18 = !DILocalVariable(name: "x", scope: !13, file: !3, line: 3, type: !16)
+!19 = !DILocation(line: 0, scope: !13)
+!20 = !DILocation(line: 4, column: 3, scope: !13)
+!21 = distinct !DISubprogram(name: "test2", scope: !3, file: !3, line: 8, type: !22, scopeLine: 8, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !25)
+!22 = !DISubroutineType(types: !23)
+!23 = !{!24}
+!24 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !8, size: 64)
+!25 = !{!26}
+!26 = !DILocalVariable(name: "x", scope: !21, file: !3, line: 9, type: !24)
+!27 = !DILocation(line: 0, scope: !21)
+!28 = !DILocation(line: 10, column: 3, scope: !21)

diff --git a/llvm/test/DebugInfo/BPF/lit.local.cfg b/llvm/test/DebugInfo/BPF/lit.local.cfg
new file mode 100644 (file)
index 0000000..a4ab262
--- /dev/null
+++ b/llvm/test/DebugInfo/BPF/lit.local.cfg
@@ -0,0 +1,2 @@
+if not 'BPF' in config.root.targets:
+    config.unsupported = True