[clang] [CIR] Add initial support for virtual base classes (PR #155534)

[Erich Keane via cfe-commits]

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@@ -238,31 +238,44 @@ void CIRGenFunction::emitCtorPrologue(const CXXConstructorDecl *cd,
   bool constructVBases = ctorType != Ctor_Base &&
                          classDecl->getNumVBases() != 0 &&
                          !classDecl->isAbstract();
-  if (constructVBases) {
-    cgm.errorNYI(cd->getSourceRange(), "emitCtorPrologue: virtual base");
-    return;
-  }
-
-  const mlir::Value oldThisValue = cxxThisValue;
-  if (!constructVBases && b != e && (*b)->isBaseInitializer() &&
-      (*b)->isBaseVirtual()) {
+  if (constructVBases &&
+      !cgm.getTarget().getCXXABI().hasConstructorVariants()) {
     cgm.errorNYI(cd->getSourceRange(),
-                 "emitCtorPrologue: virtual base initializer");
+                 "emitCtorPrologue: virtual base without variants");
     return;
   }
 
-  // Handle non-virtual base initializers.
-  for (; b != e && (*b)->isBaseInitializer(); b++) {
-    assert(!(*b)->isBaseVirtual());
+  const mlir::Value oldThisValue = cxxThisValue;
 
+  // Initialize virtual bases.
+  auto emitInitializer = [&](CXXCtorInitializer *baseInit) {
     if (cgm.getCodeGenOpts().StrictVTablePointers &&
         cgm.getCodeGenOpts().OptimizationLevel > 0 &&
-        isInitializerOfDynamicClass(*b)) {
+        isInitializerOfDynamicClass(baseInit)) {
+      // It's OK to continue after emitting the error here. The missing code
+      // just "launders" the 'this' pointer.
       cgm.errorNYI(cd->getSourceRange(),
-                   "emitCtorPrologue: strict vtable pointers");
-      return;
+                   "emitCtorPrologue: strict vtable pointers for vbase");
     }
-    emitBaseInitializer(getLoc(cd->getBeginLoc()), classDecl, *b);
+    emitBaseInitializer(getLoc(cd->getBeginLoc()), classDecl, baseInit);
+  };
+
+  for (; b != e && (*b)->isBaseInitializer() && (*b)->isBaseVirtual(); b++) {
+    if (!constructVBases)
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erichkeane wrote:

Ah, right!  I missed the same iterators.  Anything you can do to make this less awful would be appreciated :) 

https://github.com/llvm/llvm-project/pull/155534