IR: Consider two DISubprograms to be odr-equal if they have the same template parameters.

[pcc]

Summary

In ValueMapper we create new operands for MDNodes and
rely on MDNode::replaceWithUniqued to create a new MDNode
with the specified operands. However this doesn't always
actually happen correctly for DISubprograms because when we
uniquify the new node, we only odr-compare it with existing nodes
(MDNodeSubsetEqualImpl<DISubprogram>::isDeclarationOfODRMember). Although
the TemplateParameters field can refer to a distinct DICompileUnit via
DITemplateTypeParameter::type -> DICompositeType::scope -> DISubprogram::unit,
it is not currently included in the odr comparison. As a result, we can end
up getting our original DISubprogram back, which means we will have a cloned
module referring to the DICompileUnit in the original module, which causes
a verification error.

The fix I implemented was to consider TemplateParameters to be one of the
odr-equal properties. But I'm a little uncomfortable with this. In general it
seems unsound to rely on distinct MDNodes never being reachable from nodes
which we only check odr-equality of. My only long term suggestion would be
to separate odr-uniquing from full uniquing.

Test case to come.

[pcc]

It occurred to me that this may have something to do with the enableDebugTypeODRUniquing() thing, so figured we could just turn it off if we end up splitting the module. But I took a closer look at the code and discovered that they are completely separate (clang has this turned off anyway, as I'd expect). Taking a look at history it looks like both mechanisms were added around the same time. Why do we have both? Can't we have enableDebugTypeODRUniquing() also turn on the isDeclarationOfODRMember uniquing?

[krasin]

I have manually verified that this change gets rid of an assert during linking Chromium. Can you please also include a test case similar to the one mentioned in https://bugs.chromium.org/p/chromium/issues/detail?id=682773#c14?

[pcc]

• Add test case

[pcc]

• Add source

[pcc]

Ping. Since the long term fix probably won't happen any time soon, does anyone have any objection to this?

[pcc]

• Smaller test case, and add a FIXME

[aprantl]

llvm/test/Transforms/Util/clone-dicompileunit.ll

22

Can you add a short comment here that explained what is being tested?
Otherwise lgtm.

llvm/lib/IR/LLVMContextImpl.h

unsigned getHashValue() const {
     return hash_combine(Name, Scope, File, Type, Line);
   }
 };
 
 template <> struct MDNodeSubsetEqualImpl<DISubprogram> {
   typedef MDNodeKeyImpl<DISubprogram> KeyTy;
   static bool isSubsetEqual(const KeyTy &LHS, const DISubprogram *RHS) {
     return isDeclarationOfODRMember(LHS.IsDefinition, LHS.Scope,
-                                    LHS.LinkageName, RHS);
+                                    LHS.LinkageName, LHS.TemplateParams, RHS);
   }
   static bool isSubsetEqual(const DISubprogram *LHS, const DISubprogram *RHS) {
     return isDeclarationOfODRMember(LHS->isDefinition(), LHS->getRawScope(),
-                                    LHS->getRawLinkageName(), RHS);
+                                    LHS->getRawLinkageName(),
+                                    LHS->getRawTemplateParams(), RHS);
   }
 
   /// Subprograms compare equal if they declare the same function in an ODR
   /// type.
   static bool isDeclarationOfODRMember(bool IsDefinition, const Metadata *Scope,
                                        const MDString *LinkageName,
+                                       const Metadata *TemplateParams,
                                        const DISubprogram *RHS) {
     // Check whether the LHS is eligible.
     if (IsDefinition || !Scope || !LinkageName)
       return false;
 
     auto *CT = dyn_cast_or_null<DICompositeType>(Scope);
     if (!CT || !CT->getRawIdentifier())
       return false;
 
     // Compare to the RHS.
+    // FIXME: We need to compare template parameters here to avoid incorrect
+    // collisions in mapMetadata when RF_MoveDistinctMDs and a ODR-DISubprogram
+    // has a non-ODR template parameter (i.e., a DICompositeType that does not
+    // have an identifier). Eventually we should decouple ODR logic from
+    // uniquing logic.
     return IsDefinition == RHS->isDefinition() && Scope == RHS->getRawScope() &&
-           LinkageName == RHS->getRawLinkageName();
+           LinkageName == RHS->getRawLinkageName() &&
+           TemplateParams == RHS->getRawTemplateParams();
   }
 };
 
 template <> struct MDNodeKeyImpl<DILexicalBlock> {
   Metadata *Scope;
   Metadata *File;
   unsigned Line;
   unsigned Column;

llvm/test/Transforms/Util/clone-dicompileunit.ll

+; RUN: opt -run-twice -verify -disable-debug-info-type-map -S -o - %s | FileCheck %s
+
+; Generated using:
+; $ cat p.cpp
+; void sink(void *);
+; class A {
+; public:
+;   template <typename> void m_fn2() { static int a; }
+;   virtual void m_fn1();
+; };
+; void foo() {
+;   class B : public A {
+;   public:
+;     B() { m_fn2<B>(); }
+;   };
+;   sink(new B);
+; }
+; $ clang++ -target x86_64-unknown-linux -fvisibility=hidden -O2 -g2 -flto -S p.cpp -o p.ll
+; # then manually removed function/gv definitions
+
+; CHECK: DICompileUnit
+; CHECK-NOT: DICompileUnit
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux"
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!28, !29}
+!llvm.ident = !{!30}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 5.0.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3)
+!1 = !DIFile(filename: "p.cpp", directory: "/usr/local/google/home/pcc/b682773-2-repro/small2")
+!2 = !{}
+!3 = !{!4}
+!4 = !DIGlobalVariableExpression(var: !5)
+!5 = distinct !DIGlobalVariable(name: "a", scope: !6, file: !1, line: 5, type: !27, isLocal: true, isDefinition: true)
+!6 = distinct !DISubprogram(name: "m_fn2<B>", linkageName: "_ZN1A5m_fn2IZ3foovE1BEEvv", scope: !7, file: !1, line: 5, type: !8, isLocal: true, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: true, unit: !0, templateParams: !11, declaration: !23, variables: !24)
+!7 = !DICompositeType(tag: DW_TAG_class_type, name: "A", file: !1, line: 3, flags: DIFlagFwdDecl, identifier: "_ZTS1A")
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10}
+!10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !7, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!11 = !{!12}
+!12 = !DITemplateTypeParameter(type: !13)
+!13 = distinct !DICompositeType(tag: DW_TAG_class_type, name: "B", scope: !14, file: !1, line: 10, size: 64, elements: !17, vtableHolder: !7)
+!14 = distinct !DISubprogram(name: "foo", linkageName: "_Z3foov", scope: !1, file: !1, line: 9, type: !15, isLocal: false, isDefinition: true, scopeLine: 9, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !2)
+!15 = !DISubroutineType(types: !16)
+!16 = !{null}
+!17 = !{!18, !19}
+!18 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !13, baseType: !7, flags: DIFlagPublic)
+!19 = !DISubprogram(name: "B", scope: !13, file: !1, line: 12, type: !20, isLocal: false, isDefinition: false, scopeLine: 12, flags: DIFlagPublic | DIFlagPrototyped, isOptimized: true)
+!20 = !DISubroutineType(types: !21)
+!21 = !{null, !22}
+!22 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!23 = !DISubprogram(name: "m_fn2<B>", linkageName: "_ZN1A5m_fn2IZ3foovE1BEEvv", scope: !7, file: !1, line: 5, type: !8, isLocal: false, isDefinition: false, scopeLine: 5, flags: DIFlagPublic | DIFlagPrototyped, isOptimized: true, templateParams: !11)
+!24 = !{!25}
+!25 = !DILocalVariable(name: "this", arg: 1, scope: !6, type: !26, flags: DIFlagArtificial | DIFlagObjectPointer)
+!26 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !7, size: 64)
+!27 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!28 = !{i32 2, !"Dwarf Version", i32 4}
+!29 = !{i32 2, !"Debug Info Version", i32 3}
+!30 = !{!"clang version 5.0.0 "}