[clang] [DebugInfo] Ignore undefined constexpr constructors in constructor homing. (PR #218165)

[Clayton Knittel via cfe-commits]

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@@ -3239,18 +3239,36 @@ static bool canUseCtorHoming(const CXXRecordDecl *RD) {
   if (isClassOrMethodDLLImport(RD))
     return false;
 
-  if (RD->isLambda() || RD->isAggregate() ||
-      RD->hasTrivialDefaultConstructor() ||
-      RD->hasConstexprNonCopyMoveConstructor())
+  if (RD->isLambda() || RD->isAggregate() || RD->hasTrivialDefaultConstructor())
     return false;
 
+  // Skip this optimization if the class has a constexpr default constructor,
+  // since those constructors can be invoked without emitting type information
+  // for the constructor.
+  if (RD->needsImplicitDefaultConstructor() &&
+      RD->defaultedDefaultConstructorIsConstexpr())
+    return false;
+
+  bool HasNonDeletedCtor = false;
   for (const CXXConstructorDecl *Ctor : RD->ctors()) {
     if (Ctor->isCopyOrMoveConstructor())
       continue;
+    const FunctionDecl *Def = nullptr;
+    if (Ctor->isDefined(Def)) {
+      const auto *CtorDef = cast<CXXConstructorDecl>(Def);
+      // Ignore delegating constructors, the target constructor's definition
+      // will emit the type info.
+      if (CtorDef->isDelegatingConstructor())
+        continue;
----------------
ClaytonKnittel wrote:

I was writing up an argument to why it was not necessary, but I realized delegating-to-copy-ctor (or move ctor) should not enable this optimization, so we do need to check for delegating constructors in https://github.com/llvm/llvm-project/pull/218807. I updated that PR, and added two tests for delegating to copy/move ctors.

https://github.com/llvm/llvm-project/pull/218165