emit_DW_AT_noreturn flag

[vleschuk]

Summary

Support for DW_AT_noreturn DWARF flag. Add it to debug info in case function is C++11 [[ noreturn ]] or C11 _Noreturn.

PS Corresponding clang patch is following

[vleschuk]

Expanded context, added more reviewers who took part in this parts of code.

[aprantl]

Thanks for working in this!
Technically this is a DWARF 5 feature, but unknown attributes can be ignored by consumers, so there's no reason to emit it conditionally.

Could you please also add a test for llvm-dwarfdump?
Could you please also add a textual LLVM IR parser testcase?

include/llvm/IR/DebugInfoMetadata.h

1424

The \brief is redundant. We compile doxygen with autobrief now.
Also, there's a missing . at the end.

[vleschuk]

Added C++11, C11 and ObjC textual llvm-dwarfdump tests.

[aprantl]

Thanks, now all that's missing is an LLVM IR round-trip test. Adding the new flag to test/Assembler/disubprogram would work.

test/DebugInfo/noreturn_c11.ll

10

Maybe check for just a bit more context (the DW_TAG_subprogram + DW_AT_name should be fine)?

30

We typically strip out all unnecessary attributes to not distract from the testcase. A good heuristic is that you can usually get rid of everything in quotes.

test/DebugInfo/noreturn_cpp11.ll

10

More context.

37

Strip attributes.

test/DebugInfo/noreturn_objc.ll

11

more context

32

strip attributes

[vleschuk]

Stripped unnecessary attributes, added more context to CHECK

[aprantl]

LGTM on the condition that the missing IR roundtrip test (e.g., by extending test/Assembler/disubprogram.ll) is added before committing.

[aprantl]

Found one more.

test/DebugInfo/noreturn_c11.ll

11

One more thing: please rewrite this (and the other testcases) as

; CHECK: DW_TAG_subprogram 
; CHECK-NOT: DW_TAG
; CHECK: DW_AT_name{{.*}}"f"
; CHECK-NOT: DW_TAG
; CHECK: DW_AT_noreturn
``

The check for the name ensures we're in the right function, the CHECK-NOT: ensures that we are not skipping into a subsequent tag.

[vleschuk]

Added more tests

[vleschuk]

In D23167#510379, @aprantl wrote:

Found one more.

Done

include/llvm/IR/DebugInfoMetadata.h

1424

Just following the pattern in file. Added dot.

[vleschuk]

Could somebody commit this, please? I do not have the commit permissions yet.

[aprantl]

Did you forget to add the IR test before uploading the patch?

[vleschuk]

Stripped more unnecessary code. And cosmetics: trailing spaces.

[vleschuk]

In D23167#510485, @aprantl wrote:

Did you forget to add the IR test before uploading the patch?

Could you please clarify, what do you mean? All the IR tests are here now.

[aprantl]

You are adding a new constant to the LLVM IR, so there should be a round-trip test that tests the LLVM IR parser, bitcode writer, bitcode reader, and LLVM IR printer to make sure we're handling the new constant correctly.

One easy way to do this is by adding the new flag to the already existing test in test/IR/disubprogram.ll.

[vleschuk]

Added test for noreturn flag for test/Assembler/disubprogram.ll

[vleschuk]

Full context

[vleschuk]

Full context

[vleschuk]

Replied on doxygen-related comment: I do not think we should use different styles within one file.

[vleschuk]

Could somebody commit this, please?

[aprantl]

Committed as r278940. Thanks!

include/llvm/IR/DebugInfoFlags.def

 HANDLE_DI_FLAG((1 << 13), LValueReference)
 HANDLE_DI_FLAG((1 << 14), RValueReference)
 HANDLE_DI_FLAG((1 << 15), ExternalTypeRef)
 HANDLE_DI_FLAG((1 << 16), SingleInheritance)
 HANDLE_DI_FLAG((2 << 16), MultipleInheritance)
 HANDLE_DI_FLAG((3 << 16), VirtualInheritance)
 HANDLE_DI_FLAG((1 << 18), IntroducedVirtual)
 HANDLE_DI_FLAG((1 << 19), BitField)
+HANDLE_DI_FLAG((1 << 20), NoReturn)
 
 #undef HANDLE_DI_FLAG

include/llvm/IR/DebugInfoMetadata.h

public:
   /// \brief Check if this is rvalue-reference-qualified.
   ///
   /// Return true if this subprogram is a C++11 rvalue-reference-qualified
   /// non-static member function (void foo() &&).
   unsigned isRValueReference() const {
     return getFlags() & FlagRValueReference;
   }
 
+  /// \brief Check if this is marked as noreturn.
+  ///
+  /// Return true if this subprogram is C++11 noreturn or C11 _Noreturn
+  unsigned isNoReturn() const {
+    return getFlags() & FlagNoReturn;
+  }
+
   DIScopeRef getScope() const { return DIScopeRef(getRawScope()); }
 
   StringRef getName() const { return getStringOperand(2); }
   StringRef getDisplayName() const { return getStringOperand(3); }
   StringRef getLinkageName() const { return getStringOperand(4); }
 
   MDString *getRawName() const { return getOperandAs<MDString>(2); }
   MDString *getRawLinkageName() const { return getOperandAs<MDString>(4); }

include/llvm/Support/Dwarf.h

enum Attribute : uint16_t {
   DW_AT_str_offsets_base = 0x72,
   DW_AT_addr_base = 0x73,
   DW_AT_ranges_base = 0x74,
   DW_AT_dwo_id = 0x75,
   DW_AT_dwo_name = 0x76,
   DW_AT_reference = 0x77,
   DW_AT_rvalue_reference = 0x78,
   DW_AT_macros = 0x79,
+  DW_AT_noreturn = 0x87,
 
   DW_AT_lo_user = 0x2000,
   DW_AT_hi_user = 0x3fff,
 
   DW_AT_MIPS_loop_begin = 0x2002,
   DW_AT_MIPS_tail_loop_begin = 0x2003,
   DW_AT_MIPS_epilog_begin = 0x2004,
   DW_AT_MIPS_loop_unroll_factor = 0x2005,

lib/CodeGen/AsmPrinter/DwarfUnit.cpp

void DwarfUnit::applySubprogramAttributes(const DISubprogram *SP, DIE &SPDie,
   }
 
   if (SP->isLValueReference())
     addFlag(SPDie, dwarf::DW_AT_reference);
 
   if (SP->isRValueReference())
     addFlag(SPDie, dwarf::DW_AT_rvalue_reference);
 
+  if (SP->isNoReturn())
+    addFlag(SPDie, dwarf::DW_AT_noreturn);
+
   if (SP->isProtected())
     addUInt(SPDie, dwarf::DW_AT_accessibility, dwarf::DW_FORM_data1,
             dwarf::DW_ACCESS_protected);
   else if (SP->isPrivate())
     addUInt(SPDie, dwarf::DW_AT_accessibility, dwarf::DW_FORM_data1,
             dwarf::DW_ACCESS_private);
   else if (SP->isPublic())
     addUInt(SPDie, dwarf::DW_AT_accessibility, dwarf::DW_FORM_data1,

lib/Support/Dwarf.cpp

const char *llvm::dwarf::AttributeString(unsigned Attribute) {
   case DW_AT_rank:                       return "DW_AT_rank";
   case DW_AT_str_offsets_base:           return "DW_AT_str_offsets_base";
   case DW_AT_addr_base:                  return "DW_AT_addr_base";
   case DW_AT_ranges_base:                return "DW_AT_ranges_base";
   case DW_AT_dwo_id:                     return "DW_AT_dwo_id";
   case DW_AT_dwo_name:                   return "DW_AT_dwo_name";
   case DW_AT_reference:                  return "DW_AT_reference";
   case DW_AT_rvalue_reference:           return "DW_AT_rvalue_reference";
+  case DW_AT_noreturn:                   return "DW_AT_noreturn";
   case DW_AT_MIPS_loop_begin:            return "DW_AT_MIPS_loop_begin";
   case DW_AT_MIPS_tail_loop_begin:       return "DW_AT_MIPS_tail_loop_begin";
   case DW_AT_MIPS_epilog_begin:          return "DW_AT_MIPS_epilog_begin";
   case DW_AT_MIPS_loop_unroll_factor:    return "DW_AT_MIPS_loop_unroll_factor";
   case DW_AT_MIPS_software_pipeline_depth:
     return "DW_AT_MIPS_software_pipeline_depth";
   case DW_AT_MIPS_linkage_name:          return "DW_AT_MIPS_linkage_name";
   case DW_AT_MIPS_stride:                return "DW_AT_MIPS_stride";

test/DebugInfo/noreturn_c11.ll

+; RUN: %llc_dwarf -filetype=obj < %s | llvm-dwarfdump -debug-dump=info - | FileCheck %s
+; REQUIRES: object-emission
+
+; Generated by clang -S -c -std=c++11 --emit-llvm -g from the following C11 source:
+; _Noreturn void f() {
+;   throw 1;
+; }
+
+; CHECK: DW_TAG_subprogram 
+; CHECK-NOT: DW_TAG
+; CHECK: DW_AT_name{{.*}}"f"
+; CHECK-NOT: DW_TAG
+; CHECK: DW_AT_noreturn
+
+; ModuleID = './test.c'
+source_filename = "./test.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noreturn nounwind uwtable
+define void @f() #0 !dbg !6 {
+entry:
+  call void @exit(i32 0) #2, !dbg !10
+  unreachable, !dbg !10
+
+return:                                           ; No predecessors!
+  ret void, !dbg !11
+}
+
+; Function Attrs: noreturn
+declare void @exit(i32) #1
+
+attributes #0 = { noreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 4.0.0 (http://llvm.org/git/clang.git 08946d46f2add8cb241fdc09fc3731dd9dc5ecb5) (http://llvm.org/git/llvm.git d048aeecd34b8c336d1fd44e36c15b0b11c2ea4d)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "/home/del/test")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 4.0.0 (http://llvm.org/git/clang.git 08946d46f2add8cb241fdc09fc3731dd9dc5ecb5) (http://llvm.org/git/llvm.git d048aeecd34b8c336d1fd44e36c15b0b11c2ea4d)"}
+!6 = distinct !DISubprogram(name: "f", scope: !7, file: !7, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 4, flags: DIFlagNoReturn, isOptimized: false, unit: !0, variables: !2)
+!7 = !DIFile(filename: "./test.c", directory: "/home/del/test")
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !DILocation(line: 5, column: 3, scope: !6)
+!11 = !DILocation(line: 6, column: 1, scope: !6)

test/DebugInfo/noreturn_cpp11.ll

+; RUN: %llc_dwarf -filetype=obj < %s | llvm-dwarfdump -debug-dump=info - | FileCheck %s
+; REQUIRES: object-emission
+
+; Generated by clang++ -S -c -std=c++11 --emit-llvm -g from the following C++11 source:
+; [[ noreturn ]] void f() {
+;   throw 1;
+; }
+
+; CHECK: DW_TAG_subprogram 
+; CHECK-NOT: DW_TAG
+; CHECK: DW_AT_name{{.*}}"f"
+; CHECK-NOT: DW_TAG
+; CHECK: DW_AT_noreturn
+
+; ModuleID = 'test.cpp'
+source_filename = "test.cpp"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@_ZTIi = external constant i8*
+
+; Function Attrs: noreturn
+define void @_Z1fv() #0 !dbg !6 {
+entry:
+  %exception = call i8* @__cxa_allocate_exception(i64 4) #1, !dbg !9
+  %0 = bitcast i8* %exception to i32*, !dbg !9
+  store i32 1, i32* %0, align 16, !dbg !9
+  call void @__cxa_throw(i8* %exception, i8* bitcast (i8** @_ZTIi to i8*), i8* null) #2, !dbg !10
+  unreachable, !dbg !9
+
+return:                                           ; No predecessors!
+  ret void, !dbg !12
+}
+
+declare i8* @__cxa_allocate_exception(i64)
+
+declare void @__cxa_throw(i8*, i8*, i8*)
+
+attributes #0 = { noreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 4.0.0 (http://llvm.org/git/clang.git 08946d46f2add8cb241fdc09fc3731dd9dc5ecb5) (http://llvm.org/git/llvm.git d048aeecd34b8c336d1fd44e36c15b0b11c2ea4d)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.cpp", directory: "/home/del/test")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 4.0.0 (http://llvm.org/git/clang.git 08946d46f2add8cb241fdc09fc3731dd9dc5ecb5) (http://llvm.org/git/llvm.git d048aeecd34b8c336d1fd44e36c15b0b11c2ea4d)"}
+!6 = distinct !DISubprogram(name: "f", linkageName: "_Z1fv", scope: !1, file: !1, line: 1, type: !7, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped | DIFlagNoReturn, isOptimized: false, unit: !0, variables: !2)
+!7 = !DISubroutineType(types: !8)
+!8 = !{null}
+!9 = !DILocation(line: 2, column: 5, scope: !6)
+!10 = !DILocation(line: 2, column: 5, scope: !11)
+!11 = !DILexicalBlockFile(scope: !6, file: !1, discriminator: 1)
+!12 = !DILocation(line: 3, column: 1, scope: !6)

test/DebugInfo/noreturn_objc.ll

+; RUN: %llc_dwarf -filetype=obj < %s | llvm-dwarfdump -debug-dump=info - | FileCheck %s
+; REQUIRES: object-emission
+
+; Generated by clang++ -S -c --emit-llvm -g from the following ObjC source:
+; #include <stdlib.h>
+; __attribute__ ((noreturn)) void f()
+; {
+;  exit(0);
+; }
+
+; CHECK: DW_TAG_subprogram 
+; CHECK-NOT: DW_TAG
+; CHECK: DW_AT_name{{.*}}"f"
+; CHECK-NOT: DW_TAG
+; CHECK: DW_AT_noreturn
+
+; ModuleID = './test.m'
+source_filename = "./test.m"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noreturn 
+define void @f() #0 !dbg !6 {
+entry:
+  call void @exit(i32 0) #2, !dbg !10
+  unreachable, !dbg !10
+
+return:                                           ; No predecessors!
+  ret void, !dbg !11
+}
+
+; Function Attrs: noreturn
+declare void @exit(i32) #1
+
+attributes #0 = { noreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_ObjC, file: !1, producer: "clang version 4.0.0 (http://llvm.org/git/clang.git 08946d46f2add8cb241fdc09fc3731dd9dc5ecb5) (http://llvm.org/git/llvm.git d048aeecd34b8c336d1fd44e36c15b0b11c2ea4d)", isOptimized: false, runtimeVersion: 1, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.m", directory: "/home/del/test/noreturn/objc")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 4.0.0 (http://llvm.org/git/clang.git 08946d46f2add8cb241fdc09fc3731dd9dc5ecb5) (http://llvm.org/git/llvm.git d048aeecd34b8c336d1fd44e36c15b0b11c2ea4d)"}
+!6 = distinct !DISubprogram(name: "f", scope: !7, file: !7, line: 2, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagNoReturn, isOptimized: false, unit: !0, variables: !2)
+!7 = !DIFile(filename: "./test.m", directory: "/home/del/test/noreturn/objc")
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !DILocation(line: 4, column: 3, scope: !6)
+!11 = !DILocation(line: 5, column: 1, scope: !6)

unittests/IR/DebugInfoTest.cpp

#define CHECK_SPLIT(FLAGS, VECTOR, REMAINDER)                                  \
   }
   CHECK_SPLIT(DINode::FlagPublic, {DINode::FlagPublic}, 0u);
   CHECK_SPLIT(DINode::FlagProtected, {DINode::FlagProtected}, 0u);
   CHECK_SPLIT(DINode::FlagPrivate, {DINode::FlagPrivate}, 0u);
   CHECK_SPLIT(DINode::FlagVector, {DINode::FlagVector}, 0u);
   CHECK_SPLIT(DINode::FlagRValueReference, {DINode::FlagRValueReference}, 0u);
   unsigned Flags[] = {DINode::FlagFwdDecl, DINode::FlagVector};
   CHECK_SPLIT(DINode::FlagFwdDecl | DINode::FlagVector, Flags, 0u);
-  CHECK_SPLIT(0x100000u, {}, 0x100000u);
-  CHECK_SPLIT(0x100000u | DINode::FlagVector, {DINode::FlagVector}, 0x100000u);
+  CHECK_SPLIT(0x200000u, {}, 0x200000u);
+  CHECK_SPLIT(0x200000u | DINode::FlagVector, {DINode::FlagVector}, 0x200000u);
+  CHECK_SPLIT(0x200000u | DINode::FlagNoReturn, {DINode::FlagNoReturn}, 0x200000u);
 #undef CHECK_SPLIT
 }
 
 } // end namespace