[ASTImporter] Fix inequivalence of unresolved exception spec

[martong]

Summary

Structural equivalence of methods can falsely report false when the
exception specifier is unresolved (i.e unevaluated or not instantiated).

(This caused one assertion during bitcoin ctu-analysis.)

[a_sidorin]

Looks good!

clang/lib/AST/ASTImporter.cpp

3107

This looks to be true - a call adjustExceptionSpec() on the imported decl and its redeclarations can be required. Thank you for noticing this!

clang/lib/AST/ASTStructuralEquivalence.cpp

325

equivalence

[martong]

• Improve and fix typo in comments

clang/lib/AST/ASTImporter.cpp

if (GetImportedOrCreateDecl(ToFunction, D, Importer.getToContext(), DC,
       return ToFunction;
   }
 
   // Connect the redecl chain.
   if (FoundByLookup) {
     auto *Recent = const_cast<FunctionDecl *>(
           FoundByLookup->getMostRecentDecl());
     ToFunction->setPreviousDecl(Recent);
+    // FIXME Should we merge exception specifications?  E.g. In the "To"
+    // context the existing function may have exception specification with
+    // noexcept-unevaluated, while the newly imported function may have an
+    // evaluated noexcept.
   }
 
   // Import Ctor initializers.
   if (auto *FromConstructor = dyn_cast<CXXConstructorDecl>(D)) {
     if (unsigned NumInitializers = FromConstructor->getNumCtorInitializers()) {
       SmallVector<CXXCtorInitializer *, 4> CtorInitializers(NumInitializers);
       // Import first, then allocate memory and copy if there was no error.
       if (Error Err = ImportContainerChecked(

clang/lib/AST/ASTStructuralEquivalence.cpp

static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
   if (EI1.getNoCallerSavedRegs() != EI2.getNoCallerSavedRegs())
     return false;
   if (EI1.getNoCfCheck() != EI2.getNoCfCheck())
     return false;
 
   return true;
 }
 
+/// Check the eqeuivalence of exception specifications.
+static bool IsEquivalentExceptionSpec(StructuralEquivalenceContext &Context,
+                                      const FunctionProtoType *Proto1,
+                                      const FunctionProtoType *Proto2) {
+
+  auto Spec1 = Proto1->getExceptionSpecType();
+  auto Spec2 = Proto2->getExceptionSpecType();
+
+  if (isUnresolvedExceptionSpec(Spec1) || isUnresolvedExceptionSpec(Spec2))
+    return true;
+
+  if (Spec1 != Spec2)
+    return false;
+  if (Spec1 == EST_Dynamic) {
+    if (Proto1->getNumExceptions() != Proto2->getNumExceptions())
+      return false;
+    for (unsigned I = 0, N = Proto1->getNumExceptions(); I != N; ++I) {
+      if (!IsStructurallyEquivalent(Context, Proto1->getExceptionType(I),
+                                    Proto2->getExceptionType(I)))
+        return false;
+    }
+  } else if (isComputedNoexcept(Spec1)) {
+    if (!IsStructurallyEquivalent(Context, Proto1->getNoexceptExpr(),
+                                  Proto2->getNoexceptExpr()))
+      return false;
+  }
+
+  return true;
+}
+
 /// Determine structural equivalence of two types.
 static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
                                      QualType T1, QualType T2) {
   if (T1.isNull() || T2.isNull())
     return T1.isNull() && T2.isNull();
 
   QualType OrigT1 = T1;
   QualType OrigT2 = T2;
case Type::FunctionProto: {
     if (Proto1->getMethodQuals() != Proto2->getMethodQuals())
       return false;
 
     // Check exceptions, this information is lost in canonical type.
     const auto *OrigProto1 =
         cast<FunctionProtoType>(OrigT1.getDesugaredType(Context.FromCtx));
     const auto *OrigProto2 =
         cast<FunctionProtoType>(OrigT2.getDesugaredType(Context.ToCtx));
-    auto Spec1 = OrigProto1->getExceptionSpecType();
-    auto Spec2 = OrigProto2->getExceptionSpecType();
-
-    if (Spec1 != Spec2)
+    if (!IsEquivalentExceptionSpec(Context, OrigProto1, OrigProto2))
       return false;
-    if (Spec1 == EST_Dynamic) {
-      if (OrigProto1->getNumExceptions() != OrigProto2->getNumExceptions())
-        return false;
-      for (unsigned I = 0, N = OrigProto1->getNumExceptions(); I != N; ++I) {
-        if (!IsStructurallyEquivalent(Context, OrigProto1->getExceptionType(I),
-                                      OrigProto2->getExceptionType(I)))
-          return false;
-      }
-    } else if (isComputedNoexcept(Spec1)) {
-      if (!IsStructurallyEquivalent(Context, OrigProto1->getNoexceptExpr(),
-                                    OrigProto2->getNoexceptExpr()))
-        return false;
-    }
 
     // Fall through to check the bits common with FunctionNoProtoType.
     LLVM_FALLTHROUGH;
   }
 
   case Type::FunctionNoProto: {
     const auto *Function1 = cast<FunctionType>(T1);
     const auto *Function2 = cast<FunctionType>(T2);