[CIR] Add support for non-virtual base class initialization (#148080)

andykaylor · web-flow · commit 13c897093fd8 · 2025-07-11T09:57:15.000-07:00
This change adds support for initializing non-virtual base classes
during the prologue of a derived class' constructor.
diff --git a/clang/lib/CIR/CodeGen/CIRGenClass.cpp b/clang/lib/CIR/CodeGen/CIRGenClass.cpp
@@ -117,6 +117,75 @@ static void emitMemberInitializer(CIRGenFunction &cgf,
   cgf.emitInitializerForField(field, lhs, memberInit->getInit());
 }
 
+static bool isInitializerOfDynamicClass(const CXXCtorInitializer *baseInit) {
+  const Type *baseType = baseInit->getBaseClass();
+  const auto *baseClassDecl =
+      cast<CXXRecordDecl>(baseType->castAs<RecordType>()->getDecl());
+  return baseClassDecl->isDynamicClass();
+}
+
+/// Gets the address of a direct base class within a complete object.
+/// This should only be used for (1) non-virtual bases or (2) virtual bases
+/// when the type is known to be complete (e.g. in complete destructors).
+///
+/// The object pointed to by 'thisAddr' is assumed to be non-null.
+Address CIRGenFunction::getAddressOfDirectBaseInCompleteClass(
+    mlir::Location loc, Address thisAddr, const CXXRecordDecl *derived,
+    const CXXRecordDecl *base, bool baseIsVirtual) {
+  // 'thisAddr' must be a pointer (in some address space) to Derived.
+  assert(thisAddr.getElementType() == convertType(derived));
+
+  // Compute the offset of the virtual base.
+  CharUnits offset;
+  const ASTRecordLayout &layout = getContext().getASTRecordLayout(derived);
+  if (baseIsVirtual)
+    offset = layout.getVBaseClassOffset(base);
+  else
+    offset = layout.getBaseClassOffset(base);
+
+  return builder.createBaseClassAddr(loc, thisAddr, convertType(base),
+                                     offset.getQuantity(),
+                                     /*assumeNotNull=*/true);
+}
+
+void CIRGenFunction::emitBaseInitializer(mlir::Location loc,
+                                         const CXXRecordDecl *classDecl,
+                                         CXXCtorInitializer *baseInit) {
+  assert(curFuncDecl && "loading 'this' without a func declaration?");
+  assert(isa<CXXMethodDecl>(curFuncDecl));
+
+  assert(baseInit->isBaseInitializer() && "Must have base initializer!");
+
+  Address thisPtr = loadCXXThisAddress();
+
+  const Type *baseType = baseInit->getBaseClass();
+  const auto *baseClassDecl =
+      cast<CXXRecordDecl>(baseType->castAs<RecordType>()->getDecl());
+
+  bool isBaseVirtual = baseInit->isBaseVirtual();
+
+  // If the initializer for the base (other than the constructor
+  // itself) accesses 'this' in any way, we need to initialize the
+  // vtables.
+  if (classDecl->isDynamicClass()) {
+    cgm.errorNYI(loc, "emitBaseInitializer: dynamic class");
+    return;
+  }
+
+  // We can pretend to be a complete class because it only matters for
+  // virtual bases, and we only do virtual bases for complete ctors.
+  Address v = getAddressOfDirectBaseInCompleteClass(
+      loc, thisPtr, classDecl, baseClassDecl, isBaseVirtual);
+  assert(!cir::MissingFeatures::aggValueSlotGC());
+  AggValueSlot aggSlot = AggValueSlot::forAddr(
+      v, Qualifiers(), AggValueSlot::IsDestructed, AggValueSlot::IsNotAliased,
+      getOverlapForBaseInit(classDecl, baseClassDecl, isBaseVirtual));
+
+  emitAggExpr(baseInit->getInit(), aggSlot);
+
+  assert(!cir::MissingFeatures::requiresCleanups());
+}
+
 /// This routine generates necessary code to initialize base classes and
 /// non-static data members belonging to this constructor.
 void CIRGenFunction::emitCtorPrologue(const CXXConstructorDecl *cd,
@@ -154,12 +223,29 @@ void CIRGenFunction::emitCtorPrologue(const CXXConstructorDecl *cd,
     return;
   }
 
-  if ((*b)->isBaseInitializer()) {
+  const mlir::Value oldThisValue = cxxThisValue;
+  if (!constructVBases && (*b)->isBaseInitializer() && (*b)->isBaseVirtual()) {
     cgm.errorNYI(cd->getSourceRange(),
-                 "emitCtorPrologue: non-virtual base initializer");
+                 "emitCtorPrologue: virtual base initializer");
     return;
   }
 
+  // Handle non-virtual base initializers.
+  for (; b != e && (*b)->isBaseInitializer(); b++) {
+    assert(!(*b)->isBaseVirtual());
+
+    if (cgm.getCodeGenOpts().StrictVTablePointers &&
+        cgm.getCodeGenOpts().OptimizationLevel > 0 &&
+        isInitializerOfDynamicClass(*b)) {
+      cgm.errorNYI(cd->getSourceRange(),
+                   "emitCtorPrologue: strict vtable pointers");
+      return;
+    }
+    emitBaseInitializer(getLoc(cd->getBeginLoc()), classDecl, *b);
+  }
+
+  cxxThisValue = oldThisValue;
+
   if (classDecl->isDynamicClass()) {
     cgm.errorNYI(cd->getSourceRange(),
                  "emitCtorPrologue: initialize vtable pointers");
diff --git a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
@@ -1593,10 +1593,15 @@ void CIRGenFunction::emitCXXConstructExpr(const CXXConstructExpr *e,
     delegating = true;
     break;
   case CXXConstructionKind::VirtualBase:
-  case CXXConstructionKind::NonVirtualBase:
+    // This should just set 'forVirtualBase' to true and fall through, but
+    // virtual base class support is otherwise missing, so this needs to wait
+    // until it can be tested.
     cgm.errorNYI(e->getSourceRange(),
-                 "emitCXXConstructExpr: other construction kind");
+                 "emitCXXConstructExpr: virtual base constructor");
     return;
+  case CXXConstructionKind::NonVirtualBase:
+    type = Ctor_Base;
+    break;
   }
 
   emitCXXConstructorCall(cd, type, forVirtualBase, delegating, dest, e);
diff --git a/clang/lib/CIR/CodeGen/CIRGenExprAggregate.cpp b/clang/lib/CIR/CodeGen/CIRGenExprAggregate.cpp
@@ -16,6 +16,7 @@
 #include "clang/CIR/Dialect/IR/CIRAttrs.h"
 
 #include "clang/AST/Expr.h"
+#include "clang/AST/RecordLayout.h"
 #include "clang/AST/StmtVisitor.h"
 #include <cstdint>
 
@@ -362,6 +363,28 @@ void AggExprEmitter::visitCXXParenListOrInitListExpr(
       "visitCXXParenListOrInitListExpr Record or VariableSizeArray type");
 }
 
+// TODO(cir): This could be shared with classic codegen.
+AggValueSlot::Overlap_t CIRGenFunction::getOverlapForBaseInit(
+    const CXXRecordDecl *rd, const CXXRecordDecl *baseRD, bool isVirtual) {
+  // If the most-derived object is a field declared with [[no_unique_address]],
+  // the tail padding of any virtual base could be reused for other subobjects
+  // of that field's class.
+  if (isVirtual)
+    return AggValueSlot::MayOverlap;
+
+  // If the base class is laid out entirely within the nvsize of the derived
+  // class, its tail padding cannot yet be initialized, so we can issue
+  // stores at the full width of the base class.
+  const ASTRecordLayout &layout = getContext().getASTRecordLayout(rd);
+  if (layout.getBaseClassOffset(baseRD) +
+          getContext().getASTRecordLayout(baseRD).getSize() <=
+      layout.getNonVirtualSize())
+    return AggValueSlot::DoesNotOverlap;
+
+  // The tail padding may contain values we need to preserve.
+  return AggValueSlot::MayOverlap;
+}
+
 void CIRGenFunction::emitAggExpr(const Expr *e, AggValueSlot slot) {
   AggExprEmitter(*this, slot).Visit(const_cast<Expr *>(e));
 }
diff --git a/clang/lib/CIR/CodeGen/CIRGenFunction.h b/clang/lib/CIR/CodeGen/CIRGenFunction.h
@@ -562,6 +562,19 @@ class CIRGenFunction : public CIRGenTypeCache {
   }
   Address loadCXXThisAddress();
 
+  /// Convert the given pointer to a complete class to the given direct base.
+  Address getAddressOfDirectBaseInCompleteClass(mlir::Location loc,
+                                                Address value,
+                                                const CXXRecordDecl *derived,
+                                                const CXXRecordDecl *base,
+                                                bool baseIsVirtual);
+
+  /// Determine whether a base class initialization may overlap some other
+  /// object.
+  AggValueSlot::Overlap_t getOverlapForBaseInit(const CXXRecordDecl *rd,
+                                                const CXXRecordDecl *baseRD,
+                                                bool isVirtual);
+
   /// Get an appropriate 'undef' rvalue for the given type.
   /// TODO: What's the equivalent for MLIR? Currently we're only using this for
   /// void types so it just returns RValue::get(nullptr) but it'll need
@@ -762,6 +775,9 @@ class CIRGenFunction : public CIRGenTypeCache {
   void emitAutoVarCleanups(const AutoVarEmission &emission);
   void emitAutoVarInit(const AutoVarEmission &emission);
 
+  void emitBaseInitializer(mlir::Location loc, const CXXRecordDecl *classDecl,
+                           CXXCtorInitializer *baseInit);
+
   LValue emitBinaryOperatorLValue(const BinaryOperator *e);
 
   mlir::LogicalResult emitBreakStmt(const clang::BreakStmt &s);
diff --git a/clang/test/CIR/CodeGen/ctor.cpp b/clang/test/CIR/CodeGen/ctor.cpp
@@ -219,3 +219,130 @@ void init_union() {
 // CHECK-NEXT:    %[[S_ADDR:.*]] = cir.alloca {{.*}} ["s", init]
 // CHECK-NEXT:    cir.call @_ZN14UnionInitStrukC1Ev(%[[S_ADDR]])
 // CHECK-NEXT:    cir.return
+
+struct Base {
+  int a;
+  Base(int val) : a(val) {}
+};
+
+struct Derived : Base {
+  Derived(int val) : Base(val) {}
+};
+
+void test_derived() {
+  Derived d(1);
+}
+
+// CHECK: cir.func{{.*}} @_ZN4BaseC2Ei(%arg0: !cir.ptr<!rec_Base> {{.*}}, %arg1: !s32i
+// CHECK-NEXT:   %[[THIS_ADDR:.*]] = cir.alloca {{.*}} ["this", init]
+// CHECK-NEXT:   %[[VAL_ADDR:.*]] = cir.alloca {{.*}} ["val", init]
+// CHECK-NEXT:   cir.store %arg0, %[[THIS_ADDR]]
+// CHECK-NEXT:   cir.store %arg1, %[[VAL_ADDR]]
+// CHECK-NEXT:   %[[THIS:.*]] = cir.load{{.*}} %[[THIS_ADDR]]
+// CHECK-NEXT:   %[[A_ADDR:.*]] = cir.get_member %[[THIS]][0] {name = "a"}
+// CHECK-NEXT:   %[[VAL:.*]] = cir.load{{.*}} %[[VAL_ADDR]]
+// CHECK-NEXT:   cir.store{{.*}} %[[VAL]], %[[A_ADDR]]
+// CHECK-NEXT:   cir.return
+
+// CHECK:      cir.func{{.*}} @_ZN7DerivedC2Ei(%arg0: !cir.ptr<!rec_Derived> {{.*}}, %arg1: !s32i
+// CHECK-NEXT:   %[[THIS_ADDR:.*]] = cir.alloca {{.*}} ["this", init]
+// CHECK-NEXT:   %[[VAL_ADDR:.*]] = cir.alloca {{.*}} ["val", init]
+// CHECK-NEXT:   cir.store %arg0, %[[THIS_ADDR]]
+// CHECK-NEXT:   cir.store %arg1, %[[VAL_ADDR]]
+// CHECK-NEXT:   %[[THIS:.*]] = cir.load{{.*}} %[[THIS_ADDR]]
+// CHECK-NEXT:   %[[BASE:.*]] = cir.base_class_addr %[[THIS]] : !cir.ptr<!rec_Derived> nonnull [0] -> !cir.ptr<!rec_Base>
+// CHECK-NEXT:   %[[VAL:.*]] = cir.load{{.*}} %[[VAL_ADDR]]
+// CHECK-NEXT:   cir.call @_ZN4BaseC2Ei(%[[BASE]], %[[VAL]])
+// CHECK-NEXT:   cir.return
+
+// CHECK:      cir.func{{.*}} @_ZN7DerivedC1Ei(%arg0: !cir.ptr<!rec_Derived> {{.*}}, %arg1: !s32i
+// CHECK-NEXT:   %[[THIS_ADDR:.*]] = cir.alloca {{.*}} ["this", init]
+// CHECK-NEXT:   %[[VAL_ADDR:.*]] = cir.alloca {{.*}} ["val", init]
+// CHECK-NEXT:   cir.store %arg0, %[[THIS_ADDR]]
+// CHECK-NEXT:   cir.store %arg1, %[[VAL_ADDR]]
+// CHECK-NEXT:   %[[THIS:.*]] = cir.load{{.*}} %[[THIS_ADDR]]
+// CHECK-NEXT:   %[[VAL:.*]] = cir.load{{.*}} %[[VAL_ADDR]]
+// CHECK-NEXT:   cir.call @_ZN7DerivedC2Ei(%[[THIS]], %[[VAL]])
+// CHECK-NEXT:   cir.return
+
+// CHECK: cir.func{{.*}} @_Z12test_derivedv
+// CHECK-NEXT:    %[[D_ADDR:.*]] = cir.alloca {{.*}} ["d", init]
+// CHECK-NEXT:    %[[ONE:.*]] = cir.const #cir.int<1> : !s32i
+// CHECK-NEXT:    cir.call @_ZN7DerivedC1Ei(%[[D_ADDR]], %[[ONE]])
+// CHECK-NEXT:    cir.return
+
+struct Base2 {
+  int b;
+  Base2(int val) : b(val) {}
+};
+
+struct Derived2 : Base, Base2 {
+  int c;
+  Derived2(int val1, int val2, int val3) : Base(val1), Base2(val2), c(val3) {}
+};
+
+void test_derived2() {
+  Derived2 d(1, 2, 3);
+}
+
+// CHECK: cir.func{{.*}} @_ZN5Base2C2Ei(%arg0: !cir.ptr<!rec_Base2> {{.*}}, %arg1: !s32i
+// CHECK-NEXT:   %[[THIS_ADDR:.*]] = cir.alloca {{.*}} ["this", init]
+// CHECK-NEXT:   %[[VAL_ADDR:.*]] = cir.alloca {{.*}} ["val", init]
+// CHECK-NEXT:   cir.store %arg0, %[[THIS_ADDR]]
+// CHECK-NEXT:   cir.store %arg1, %[[VAL_ADDR]]
+// CHECK-NEXT:   %[[THIS:.*]] = cir.load{{.*}} %[[THIS_ADDR]]
+// CHECK-NEXT:   %[[B_ADDR:.*]] = cir.get_member %[[THIS]][0] {name = "b"}
+// CHECK-NEXT:   %[[VAL:.*]] = cir.load{{.*}} %[[VAL_ADDR]]
+// CHECK-NEXT:   cir.store{{.*}} %[[VAL]], %[[B_ADDR]]
+// CHECK-NEXT:   cir.return
+
+// CHECK:      cir.func{{.*}} @_ZN8Derived2C2Eiii(%arg0: !cir.ptr<!rec_Derived2>
+// CHECK-SAME:                                    %arg1: !s32i
+// CHECK-SAME:                                    %arg2: !s32i
+// CHECK-SAME:                                    %arg3: !s32i
+// CHECK-NEXT:   %[[THIS_ADDR:.*]] = cir.alloca {{.*}} ["this", init]
+// CHECK-NEXT:   %[[VAL1_ADDR:.*]] = cir.alloca {{.*}} ["val1", init]
+// CHECK-NEXT:   %[[VAL2_ADDR:.*]] = cir.alloca {{.*}} ["val2", init]
+// CHECK-NEXT:   %[[VAL3_ADDR:.*]] = cir.alloca {{.*}} ["val3", init]
+// CHECK-NEXT:   cir.store %arg0, %[[THIS_ADDR]]
+// CHECK-NEXT:   cir.store %arg1, %[[VAL1_ADDR]]
+// CHECK-NEXT:   cir.store %arg2, %[[VAL2_ADDR]]
+// CHECK-NEXT:   cir.store %arg3, %[[VAL3_ADDR]]
+// CHECK-NEXT:   %[[THIS:.*]] = cir.load{{.*}} %[[THIS_ADDR]]
+// CHECK-NEXT:   %[[BASE:.*]] = cir.base_class_addr %[[THIS]] : !cir.ptr<!rec_Derived2> nonnull [0] -> !cir.ptr<!rec_Base>
+// CHECK-NEXT:   %[[VAL1:.*]] = cir.load{{.*}} %[[VAL1_ADDR]]
+// CHECK-NEXT:   cir.call @_ZN4BaseC2Ei(%[[BASE]], %[[VAL1]])
+// CHECK-NEXT:   %[[BASE2:.*]] = cir.base_class_addr %[[THIS]] : !cir.ptr<!rec_Derived2> nonnull [4] -> !cir.ptr<!rec_Base2>
+// CHECK-NEXT:   %[[VAL2:.*]] = cir.load{{.*}} %[[VAL2_ADDR]]
+// CHECK-NEXT:   cir.call @_ZN5Base2C2Ei(%[[BASE2]], %[[VAL2]])
+// CHECK-NEXT:   %[[C_ADDR:.*]] = cir.get_member %[[THIS]][2] {name = "c"}
+// CHECK-NEXT:   %[[VAL3:.*]] = cir.load{{.*}} %[[VAL3_ADDR]]
+// CHECK-NEXT:   cir.store{{.*}} %[[VAL3]], %[[C_ADDR]]
+// CHECK-NEXT:   cir.return
+
+// CHECK:      cir.func{{.*}} @_ZN8Derived2C1Eiii(%arg0: !cir.ptr<!rec_Derived2>
+// CHECK-SAME:                                    %arg1: !s32i
+// CHECK-SAME:                                    %arg2: !s32i
+// CHECK-SAME:                                    %arg3: !s32i
+// CHECK-NEXT:   %[[THIS_ADDR:.*]] = cir.alloca {{.*}} ["this", init]
+// CHECK-NEXT:   %[[VAL1_ADDR:.*]] = cir.alloca {{.*}} ["val1", init]
+// CHECK-NEXT:   %[[VAL2_ADDR:.*]] = cir.alloca {{.*}} ["val2", init]
+// CHECK-NEXT:   %[[VAL3_ADDR:.*]] = cir.alloca {{.*}} ["val3", init]
+// CHECK-NEXT:   cir.store %arg0, %[[THIS_ADDR]]
+// CHECK-NEXT:   cir.store %arg1, %[[VAL1_ADDR]]
+// CHECK-NEXT:   cir.store %arg2, %[[VAL2_ADDR]]
+// CHECK-NEXT:   cir.store %arg3, %[[VAL3_ADDR]]
+// CHECK-NEXT:   %[[THIS:.*]] = cir.load{{.*}} %[[THIS_ADDR]]
+// CHECK-NEXT:   %[[VAL1:.*]] = cir.load{{.*}} %[[VAL1_ADDR]]
+// CHECK-NEXT:   %[[VAL2:.*]] = cir.load{{.*}} %[[VAL2_ADDR]]
+// CHECK-NEXT:   %[[VAL3:.*]] = cir.load{{.*}} %[[VAL3_ADDR]]
+// CHECK-NEXT:   cir.call @_ZN8Derived2C2Eiii(%[[THIS]], %[[VAL1]], %[[VAL2]], %[[VAL3]])
+// CHECK-NEXT:   cir.return
+
+// CHECK: cir.func{{.*}} @_Z13test_derived2v
+// CHECK-NEXT:    %[[D_ADDR:.*]] = cir.alloca {{.*}} ["d", init]
+// CHECK-NEXT:    %[[ONE:.*]] = cir.const #cir.int<1> : !s32i
+// CHECK-NEXT:    %[[TWO:.*]] = cir.const #cir.int<2> : !s32i
+// CHECK-NEXT:    %[[THREE:.*]] = cir.const #cir.int<3> : !s32i
+// CHECK-NEXT:    cir.call @_ZN8Derived2C1Eiii(%[[D_ADDR]], %[[ONE]], %[[TWO]], %[[THREE]])
+// CHECK-NEXT:    cir.return
