Fix assertion when generating debug information for deduced template specialization types.

[EricWF]

Summary

Currently the following code hits an llvm_unreachable in CGDebugInfo::CreateTypeNode because DeducedTemplateSpecialization isn't handled.

// clang++ -std=c++1z -g test.cpp
template <class T> struct S { S(T) {} };
S s(42);

This patch attempts to fix the handling of DeducedTemplateSpecialization as to correctly emit debug information. I've also attempted to write a test checking the emission of the debug information, but IDK if it's testing for the right output.

[EricWF]

Remove unintentional changes.

[majnemer]

lib/CodeGen/CGDebugInfo.cpp

2479

You are unconditionally dereferencing a dyn_cast, this seems bad. Is T sometimes not a DeducedType or should the dyn_cast be a cast?

[EricWF]

lib/CodeGen/CGDebugInfo.cpp

2479

Woops that should have been a cast instead of a dyn_cast. T should always be DeducedType (See AstContext.cpp:1879 for an example use of cast<DeducedType>(...) ).

[EricWF]

Address @majnemer's comments.

[EricWF]

lib/CodeGen/CGDebugInfo.cpp

2478

I'll put this in alphabetical order before committing.

[rsmith]

lib/CodeGen/CGDebugInfo.cpp

2478

Reuse the Type::Auto case here rather than duplicating it. (You'll need to change its AutoType to the DeducedType common base class.)

[EricWF]

Address @rsmith's review comments.

[rsmith]

LGTM, thanks!

lib/CodeGen/CGDebugInfo.cpp

       T = cast<ElaboratedType>(T)->getNamedType();
       break;
     case Type::Paren:
       T = cast<ParenType>(T)->getInnerType();
       break;
     case Type::SubstTemplateTypeParm:
       T = cast<SubstTemplateTypeParmType>(T)->getReplacementType();
       break;
-    case Type::Auto: {
-      QualType DT = cast<AutoType>(T)->getDeducedType();
+    case Type::Auto:
+    case Type::DeducedTemplateSpecialization: {
+      QualType DT = cast<DeducedType>(T)->getDeducedType();
       assert(!DT.isNull() && "Undeduced types shouldn't reach here.");
       T = DT;
       break;
     }
     case Type::Adjusted:
     case Type::Decayed:
       // Decayed and adjusted types use the adjusted type in LLVM and DWARF.
       T = cast<AdjustedType>(T)->getAdjustedType();

test/CodeGenCXX/debug-info-template-deduction-guide.cpp

+// RUN: %clang -S -emit-llvm -target x86_64-unknown_unknown -g %s -o - -std=c++1z | FileCheck %s
+
+// Verify that we don't crash when emitting debug information for objects
+// created from a deduced template specialization.
+
+template <class T>
+struct S {
+  S(T) {}
+};
+
+// CHECK: !DIGlobalVariable(name: "s1"
+// CHECK-SAME: type: [[TYPE_NUM:![0-9]+]]
+// CHECK: !DIGlobalVariable(name: "s2"
+// CHECK-SAME: type: [[TYPE_NUM]]
+// CHECK: [[TYPE_NUM]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S<int>",
+S s1(42);
+S<int> s2(42);