[ThinLTO] Fix a crash in lazy loading of Metadata

This is a revised version of D41474.

When the debug location is parsed in BitcodeReader::parseFunction, the
scope and inlinedAt MDNodes are obtained via MDLoader->getMDNodeFwdRefOrNull(),
which will create a forward ref if they were not yet loaded.
Specifically, if one of these MDNodes is in the module level metadata
block, and this is during ThinLTO importing, that metadata block is
lazily loaded.

Most places in that invoke getMDNodeFwdRefOrNull have a corresponding call
to resolveForwardRefsAndPlaceholders which will take care of resolving them.
E.g. places that call getMetadataFwdRefOrLoad, or at the end of parsing a
function-level metadata block, or at the end of the initial lazy load of
module level metadata in order to handle invocations of getMDNodeFwdRefOrNull
for named metadata and global object attachments. However, the calls for
the scope/inlinedAt of debug locations are not backed by any such call to
resolveForwardRefsAndPlaceholders.

To fix this, change the scope and inlinedAt parsing to instead use
getMetadataFwdRefOrLoad, which will ensure the forward refs to lazily
loaded metadata are resolved.

Fixes PR35472.

llvm-svn: 346891

3 files changed, 139 insertions, 2 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 3b1d54f82cb..5f5167c9a2e 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -3548,12 +3548,14 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
 
       MDNode *Scope = nullptr, *IA = nullptr;
       if (ScopeID) {
-        Scope = MDLoader->getMDNodeFwdRefOrNull(ScopeID - 1);
+        Scope = dyn_cast_or_null<MDNode>(
+            MDLoader->getMetadataFwdRefOrLoad(ScopeID - 1));
         if (!Scope)
           return error("Invalid record");
       }
       if (IAID) {
-        IA = MDLoader->getMDNodeFwdRefOrNull(IAID - 1);
+        IA = dyn_cast_or_null<MDNode>(
+            MDLoader->getMetadataFwdRefOrLoad(IAID - 1));
         if (!IA)
           return error("Invalid record");
       }
diff --git a/llvm/test/ThinLTO/X86/Inputs/pr35472.ll b/llvm/test/ThinLTO/X86/Inputs/pr35472.ll
new file mode 100644
index 00000000000..b9c92b3e3fb
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/Inputs/pr35472.ll
@@ -0,0 +1,13 @@
+; ModuleID = 'b.cpp'
+source_filename = "b.cpp"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline optnone uwtable
+define void @_Z5Alphav() {
+entry:
+  call void @_Z5Bravov()
+  ret void
+}
+
+declare void @_Z5Bravov()
diff --git a/llvm/test/ThinLTO/X86/pr35472.ll b/llvm/test/ThinLTO/X86/pr35472.ll
new file mode 100644
index 00000000000..96a95aa4636
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/pr35472.ll
@@ -0,0 +1,122 @@
+; Test to make sure that lazily loaded debug location scope metadata is
+; handled properly. Note that we need to have the DILexicalScope !34
+; referenced from multiple function's debug locs for this to be in the
+; lazily loaded module level metadata block.
+
+; RUN: opt -module-hash -module-summary %s -o %t1.bc
+; RUN: opt -module-hash -module-summary %p/Inputs/pr35472.ll -o %t2.bc
+; RUN: llvm-lto -thinlto-action=run %t1.bc %t2.bc -exported-symbol=_Z5Alphav
+; RUN: llvm-nm %t1.bc.thinlto.o | FileCheck %s -check-prefix=ThinLTOa
+; RUN: llvm-nm %t2.bc.thinlto.o | FileCheck %s -check-prefix=ThinLTOb
+
+; ThinLTOa-DAG: T _Z5Bravov
+; ThinLTOa-DAG: W _ZN4EchoD2Ev
+; ThinLTOb-DAG: T _Z5Alphav
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.Delta = type { %struct.Charlie }
+%struct.Charlie = type { i32 }
+%struct.Echo = type { %struct.Charlie }
+
+$_ZN4EchoD2Ev = comdat any
+$_ZN5DeltaD2Ev = comdat any
+
+define void @_Z5Bravov() !dbg !7 {
+  %Hotel = alloca %struct.Delta, align 4
+  %India = alloca %struct.Echo, align 4
+  call void @llvm.dbg.declare(metadata %struct.Delta* %Hotel, metadata !10, metadata !DIExpression()), !dbg !22
+  call void @_ZN4EchoD2Ev(%struct.Echo* %India), !dbg !28
+  ret void, !dbg !28
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+define linkonce_odr void @_ZN4EchoD2Ev(%struct.Echo* %this) unnamed_addr comdat align 2 {
+  %this.addr.i = alloca %struct.Charlie*, align 8
+  call void @llvm.dbg.declare(metadata %struct.Charlie** %this.addr.i, metadata !29, metadata !DIExpression()), !dbg !32
+  %this1.i = load %struct.Charlie*, %struct.Charlie** %this.addr.i, align 8
+  %Golf.i = getelementptr inbounds %struct.Charlie, %struct.Charlie* %this1.i, i32 0, i32 0, !dbg !33
+  ret void
+}
+
+define linkonce_odr void @_ZN5DeltaD2Ev(%struct.Delta* %this) unnamed_addr comdat align 2 !dbg !36 {
+  %this.addr.i = alloca %struct.Charlie*, align 8
+  call void @llvm.dbg.declare(metadata %struct.Charlie** %this.addr.i, metadata !29, metadata !DIExpression()), !dbg !41
+  %this1.i = load %struct.Charlie*, %struct.Charlie** %this.addr.i, align 8
+  %Golf.i = getelementptr inbounds %struct.Charlie, %struct.Charlie* %this1.i, i32 0, i32 0, !dbg !48
+  ret void
+}
+
+!llvm.module.flags = !{!3, !4, !5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 321056)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "a.cpp", directory: "/home/sunil/185335/302")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!7 = distinct !DISubprogram(name: "Bravo", linkageName: "_Z5Bravov", scope: !1, file: !1, line: 17, type: !8, isLocal: false, isDefinition: true, scopeLine: 17, flags: DIFlagPrototyped, isOptimized: false, unit: !0)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !DILocalVariable(name: "Hotel", scope: !7, file: !1, line: 18, type: !11)
+!11 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Delta", file: !1, line: 6, size: 32, elements: !12, identifier: "_ZTS5Delta")
+!12 = !{!13}
+!13 = !DIDerivedType(tag: DW_TAG_member, name: "Foxtrot", scope: !11, file: !1, line: 7, baseType: !14, size: 32)
+!14 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Charlie", file: !1, line: 1, size: 32, elements: !15, identifier: "_ZTS7Charlie")
+!15 = !{!16, !18}
+!16 = !DIDerivedType(tag: DW_TAG_member, name: "Golf", scope: !14, file: !1, line: 3, baseType: !17, size: 32)
+!17 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!18 = !DISubprogram(name: "~Charlie", scope: !14, file: !1, line: 2, type: !19, isLocal: false, isDefinition: false, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false)
+!19 = !DISubroutineType(types: !20)
+!20 = !{null, !21}
+!21 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !14, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!22 = !DILocation(line: 18, column: 11, scope: !7)
+!24 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Echo", file: !1, line: 10, size: 32, elements: !25, identifier: "_ZTS4Echo")
+!25 = !{!26}
+!26 = !DIDerivedType(tag: DW_TAG_member, name: "Foxtrot", scope: !24, file: !1, line: 11, baseType: !14, size: 32)
+!28 = !DILocation(line: 20, column: 1, scope: !7)
+!29 = !DILocalVariable(name: "this", arg: 1, scope: !30, type: !31, flags: DIFlagArtificial | DIFlagObjectPointer)
+!30 = distinct !DISubprogram(name: "~Charlie", linkageName: "_ZN7CharlieD2Ev", scope: !14, file: !1, line: 2, type: !19, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !18)
+!31 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !14, size: 64)
+!32 = !DILocation(line: 0, scope: !30)
+!33 = !DILocation(line: 2, column: 53, scope: !34)
+!34 = distinct !DILexicalBlock(scope: !30, file: !1, line: 2, column: 51)
+!36 = distinct !DISubprogram(name: "~Delta", linkageName: "_ZN5DeltaD2Ev", scope: !11, file: !1, line: 6, type: !37, isLocal: false, isDefinition: true, scopeLine: 6, flags: DIFlagArtificial | DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !40)
+!37 = !DISubroutineType(types: !38)
+!38 = !{null, !39}
+!39 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !11, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!40 = !DISubprogram(name: "~Delta", scope: !11, type: !37, isLocal: false, isDefinition: false, flags: DIFlagArtificial | DIFlagPrototyped, isOptimized: false)
+!41 = !DILocation(line: 0, scope: !30, inlinedAt: !42)
+!42 = distinct !DILocation(line: 6, column: 8, scope: !43)
+!43 = distinct !DILexicalBlock(scope: !36, file: !1, line: 6, column: 8)
+!48 = !DILocation(line: 2, column: 53, scope: !34, inlinedAt: !42)
+
+;----------------------------------------------------------------------------------------------
+; Compiled from following two source files with 'clang++ -S --std=c++11 -O0 -g -flto=thin' 
+; struct Charlie {
+;     __attribute__((__always_inline__)) ~Charlie() { Golf = 0; }
+;     int Golf;
+; };
+; 
+; struct Delta {
+;     Charlie Foxtrot;
+; };
+; 
+; struct Echo {
+;     Charlie Foxtrot;
+;     __attribute__((nodebug)) ~Echo() = default;
+; };
+; 
+; extern void Bravo();
+; 
+; void Bravo() {
+;     Delta Hotel;
+;     Echo India;
+; }
+; -----------------------------
+; extern void Bravo();
+; extern void Alpha();
+; void Alpha() { Bravo(); }
+