Fix an assert when mixing -g and -gmlt in LTO

[probinson]

Summary

This is the other half of PR31437, split off from D29310.

Remove an assertion that doesn't hold when mixing -g and -gmlt compilation
units. Replace it with a morally equivalent assertion.

[dblaikie]

Not sure if the new assert is 'equivalent' (but as you & my past self (in that comment) say, the old one was wrong... so)

Looks good - thanks for working up the test cases & investigation!

[probinson]

I'll call it "related" in the commit log. The common idea is that new abstract variables should not appear in the absence of an abstract scope.
Thanks!

llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

 
 DbgVariable *DwarfDebug::getExistingAbstractVariable(InlinedVariable IV) {
   const DILocalVariable *Cleansed;
   return getExistingAbstractVariable(IV, Cleansed);
 }
 
 void DwarfDebug::createAbstractVariable(const DILocalVariable *Var,
                                         LexicalScope *Scope) {
+  assert(Scope && Scope->isAbstractScope());
   auto AbsDbgVariable = make_unique<DbgVariable>(Var, /* IA */ nullptr);
   InfoHolder.addScopeVariable(Scope, AbsDbgVariable.get());
   AbstractVariables[Var] = std::move(AbsDbgVariable);
 }
 
 void DwarfDebug::ensureAbstractVariableIsCreated(InlinedVariable IV,
                                                  const MDNode *ScopeNode) {
   const DILocalVariable *Cleansed = nullptr;
void DwarfDebug::endFunction(const MachineFunction *MF) {
 
   // Under -gmlt, skip building the subprogram if there are no inlined
   // subroutines inside it. But with -fdebug-info-for-profiling, the subprogram
   // is still needed as we need its source location.
   if (!TheCU.getCUNode()->getDebugInfoForProfiling() &&
       TheCU.getCUNode()->getEmissionKind() == DICompileUnit::LineTablesOnly &&
       LScopes.getAbstractScopesList().empty() && !IsDarwin) {
     assert(InfoHolder.getScopeVariables().empty());
-    // FIXME: This wouldn't be true in LTO with a -g (with inlining) CU followed
-    // by a -gmlt CU. Add a test and remove this assertion.
-    assert(AbstractVariables.empty());
     PrevLabel = nullptr;
     CurFn = nullptr;
     DebugHandlerBase::endFunction(MF);
     return;
   }
 
 #ifndef NDEBUG
   size_t NumAbstractScopes = LScopes.getAbstractScopesList().size();

llvm/trunk/test/DebugInfo/X86/dbg-abstract-vars-g-gmlt.ll

+; RUN: llc < %s -filetype=obj | llvm-dwarfdump - -debug-dump=info | FileCheck %s
+;
+; IR module created as follows:
+;   clang -emit-llvm -S db-abs-1.cpp -o db-abs-1.ll -g
+;   clang -emit-llvm -S db-abs-2.cpp -o db-abs-2.ll -gmlt
+;   llvm-link db-abs-1.ll db-abs-2.ll -S -o db-abs-3.ll
+; --- db-abs-1.cpp ---
+; void f1();
+; inline __attribute__((always_inline)) void f2(int) {
+;   f1();
+; }
+; void f3() {
+;   f2(0);
+; }
+; --- db-abs-2.cpp ---
+; void f() {
+; }
+; ---
+; The point is that f3() is compiled -g and we get an abstract variable for the
+; unnamed parameter to f2(); then f() is compiled -gmlt and it's okay to have
+; the abstract variable still there.
+; PR31437.
+;
+; (The 'always_inline' attribute forces f2() to be inlined even at -O0, the 
+; 'inline' keyword means the non-inlined definition of f2() can be omitted from
+; the IR.  These are just tactics to simplify the generated test case.)
+;
+; Verify we see the formal parameter in the first compile-unit, and nothing in
+; the second compile-unit.
+;
+; CHECK:      DW_TAG_compile_unit
+; CHECK-NOT:  DW_TAG
+; CHECK:      DW_AT_name {{.*}} "db-abs-1.cpp"
+; CHECK-NOT:  NULL
+; CHECK:      DW_TAG_subprogram
+; CHECK-NEXT: DW_AT_linkage_name {{.*}} "_Z2f2i"
+; CHECK-NOT:  {{DW_TAG|NULL}}
+; CHECK:      DW_TAG_formal_parameter
+; CHECK-NOT:  DW_AT_name
+; CHECK:      {{DW_TAG|NULL}}
+; CHECK:      DW_TAG_inlined_subroutine
+; CHECK-NEXT: DW_AT_abstract_origin {{.*}} "_Z2f2i"
+
+; CHECK:      DW_TAG_compile_unit
+; CHECK-NOT:  DW_TAG
+
+; ModuleID = 'llvm-link'
+source_filename = "llvm-link"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline uwtable
+define void @_Z2f3v() #0 !dbg !8 {
+entry:
+  %.addr.i = alloca i32, align 4
+  call void @llvm.dbg.declare(metadata i32* %.addr.i, metadata !11, metadata !16), !dbg !17
+  store i32 0, i32* %.addr.i, align 4
+  call void @_Z2f1v(), !dbg !19
+  ret void, !dbg !20
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+declare void @_Z2f1v() #2
+
+; Function Attrs: noinline nounwind uwtable
+define void @_Z1fv() #3 !dbg !21 {
+entry:
+  ret void, !dbg !23
+}
+
+attributes #0 = { noinline uwtable }
+attributes #1 = { nounwind readnone }
+attributes #2 = { nounwind }
+attributes #3 = { noinline nounwind uwtable }
+
+!llvm.dbg.cu = !{!0, !3}
+!llvm.ident = !{!5, !5}
+!llvm.module.flags = !{!6, !7}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 5.0.0 (trunk 293745)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "db-abs-1.cpp", directory: "/home/probinson/projects/scratch/pr31437")
+!2 = !{}
+!3 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !4, producer: "clang version 5.0.0 (trunk 293745)", isOptimized: false, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!4 = !DIFile(filename: "db-abs-2.cpp", directory: "/home/probinson/projects/scratch/pr31437")
+!5 = !{!"clang version 5.0.0 (trunk 293745)"}
+!6 = !{i32 2, !"Dwarf Version", i32 4}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = distinct !DISubprogram(name: "f3", linkageName: "_Z2f3v", scope: !1, file: !1, line: 5, type: !9, isLocal: false, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!9 = !DISubroutineType(types: !10)
+!10 = !{null}
+!11 = !DILocalVariable(arg: 1, scope: !12, file: !1, line: 2, type: !15)
+!12 = distinct !DISubprogram(name: "f2", linkageName: "_Z2f2i", scope: !1, file: !1, line: 2, type: !13, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!13 = !DISubroutineType(types: !14)
+!14 = !{null, !15}
+!15 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!16 = !DIExpression()
+!17 = !DILocation(line: 2, column: 50, scope: !12, inlinedAt: !18)
+!18 = distinct !DILocation(line: 6, column: 3, scope: !8)
+!19 = !DILocation(line: 3, column: 3, scope: !12, inlinedAt: !18)
+!20 = !DILocation(line: 7, column: 1, scope: !8)
+!21 = distinct !DISubprogram(name: "f", scope: !4, file: !4, line: 1, type: !22, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: false, unit: !3, variables: !2)
+!22 = !DISubroutineType(types: !2)
+!23 = !DILocation(line: 2, column: 1, scope: !21)