[CIR] Add support for delegating constructor initialization (llvm#156757)

andykaylor · web-flow · commit 83da177dba86 · 2025-09-04T14:00:31.000-07:00
This adds support for zero-initialization during delegating constructor
processing.

Note, this also adds code to skip emitting constructors that are trivial
and default to match the classic codegen behavior. The incubator does
not skip these constructors, but I have found a case where this results
in a call to a default constructor that is never defined.
diff --git a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
@@ -1966,15 +1966,23 @@ void CIRGenFunction::emitCXXConstructExpr(const CXXConstructExpr *e,
   // constructor, emit the zero initialization now, unless destination is
   // already zeroed.
   if (e->requiresZeroInitialization() && !dest.isZeroed()) {
-    cgm.errorNYI(e->getSourceRange(),
-                 "emitCXXConstructExpr: requires initialization");
-    return;
+    switch (e->getConstructionKind()) {
+    case CXXConstructionKind::Delegating:
+    case CXXConstructionKind::Complete:
+      emitNullInitialization(getLoc(e->getSourceRange()), dest.getAddress(),
+                             e->getType());
+      break;
+    case CXXConstructionKind::VirtualBase:
+    case CXXConstructionKind::NonVirtualBase:
+      cgm.errorNYI(e->getSourceRange(),
+                   "emitCXXConstructExpr: base requires initialization");
+      break;
+    }
   }
 
-  // If this is a call to a trivial default constructor:
-  // In LLVM: do nothing.
-  // In CIR: emit as a regular call, other later passes should lower the
-  // ctor call into trivial initialization.
+  // If this is a call to a trivial default constructor, do nothing.
+  if (cd->isTrivial() && cd->isDefaultConstructor())
+    return;
 
   // Elide the constructor if we're constructing from a temporary
   if (getLangOpts().ElideConstructors && e->isElidable()) {
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -1368,6 +1368,15 @@ mlir::LogicalResult CIRToLLVMConstantOpLowering::matchAndRewrite(
     rewriter.replaceOp(op, lowerCirAttrAsValue(op, op.getValue(), rewriter,
                                                getTypeConverter()));
     return mlir::success();
+  } else if (auto recTy = mlir::dyn_cast<cir::RecordType>(op.getType())) {
+    if (mlir::isa<cir::ZeroAttr, cir::UndefAttr>(attr)) {
+      mlir::Value initVal =
+          lowerCirAttrAsValue(op, attr, rewriter, typeConverter);
+      rewriter.replaceOp(op, initVal);
+      return mlir::success();
+    }
+    return op.emitError() << "unsupported lowering for record constant type "
+                          << op.getType();
   } else if (auto complexTy = mlir::dyn_cast<cir::ComplexType>(op.getType())) {
     mlir::Type complexElemTy = complexTy.getElementType();
     mlir::Type complexElemLLVMTy = typeConverter->convertType(complexElemTy);
diff --git a/clang/test/CIR/CodeGen/delegating-ctor.cpp b/clang/test/CIR/CodeGen/delegating-ctor.cpp
@@ -0,0 +1,72 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s --check-prefix=CIR
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s --check-prefix=LLVM
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s --check-prefix=OGCG
+
+struct Delegating {
+  Delegating();
+  Delegating(int);
+};
+
+// Check that the constructor being delegated to is called with the correct
+// arguments.
+Delegating::Delegating() : Delegating(0) {}
+
+// CIR: cir.func {{.*}} @_ZN10DelegatingC2Ev(%[[THIS_ARG:.*]]: !cir.ptr<!rec_Delegating> {{.*}})
+// CIR:   %[[THIS_ADDR:.*]] = cir.alloca !cir.ptr<!rec_Delegating>, !cir.ptr<!cir.ptr<!rec_Delegating>>, ["this", init]
+// CIR:   cir.store{{.*}} %[[THIS_ARG]], %[[THIS_ADDR]]
+// CIR:   %[[THIS:.*]] = cir.load %[[THIS_ADDR]]
+// CIR:   %[[ZERO:.*]] = cir.const #cir.int<0> : !s32i
+// CIR:   cir.call @_ZN10DelegatingC2Ei(%[[THIS]], %[[ZERO]]) : (!cir.ptr<!rec_Delegating>, !s32i) -> ()
+
+// LLVM: define {{.*}} @_ZN10DelegatingC2Ev(ptr %[[THIS_ARG:.*]])
+// LLVM:   %[[THIS_ADDR:.*]] = alloca ptr
+// LLVM:   store ptr %[[THIS_ARG]], ptr %[[THIS_ADDR]]
+// LLVM:   %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
+// LLVM:   call void @_ZN10DelegatingC2Ei(ptr %[[THIS]], i32 0)
+
+// OGCG: define {{.*}} @_ZN10DelegatingC2Ev(ptr {{.*}} %[[THIS_ARG:.*]])
+// OGCG:   %[[THIS_ADDR:.*]] = alloca ptr
+// OGCG:   store ptr %[[THIS_ARG]], ptr %[[THIS_ADDR]]
+// OGCG:   %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
+// OGCG:   call void @_ZN10DelegatingC2Ei(ptr {{.*}} %[[THIS]], i32 {{.*}} 0)
+
+struct DelegatingWithZeroing {
+  int i;
+  DelegatingWithZeroing() = default;
+  DelegatingWithZeroing(int);
+};
+
+// Check that the delegating constructor performs zero-initialization here.
+// FIXME: we should either emit the trivial default constructor or remove the
+// call to it in a lowering pass.
+DelegatingWithZeroing::DelegatingWithZeroing(int) : DelegatingWithZeroing() {}
+
+// CIR: cir.func {{.*}} @_ZN21DelegatingWithZeroingC2Ei(%[[THIS_ARG:.*]]: !cir.ptr<!rec_DelegatingWithZeroing> {{.*}}, %[[I_ARG:.*]]: !s32i {{.*}})
+// CIR:   %[[THIS_ADDR:.*]] = cir.alloca !cir.ptr<!rec_DelegatingWithZeroing>, !cir.ptr<!cir.ptr<!rec_DelegatingWithZeroing>>, ["this", init]
+// CIR:   %[[I_ADDR:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["", init]
+// CIR:   cir.store{{.*}} %[[THIS_ARG]], %[[THIS_ADDR]]
+// CIR:   cir.store{{.*}} %[[I_ARG]], %[[I_ADDR]]
+// CIR:   %[[THIS:.*]] = cir.load %[[THIS_ADDR]]
+// CIR:   %[[ZERO:.*]] = cir.const #cir.zero : !rec_DelegatingWithZeroing
+// CIR:   cir.store{{.*}} %[[ZERO]], %[[THIS]] : !rec_DelegatingWithZeroing, !cir.ptr<!rec_DelegatingWithZeroing>
+
+// LLVM: define {{.*}} void @_ZN21DelegatingWithZeroingC2Ei(ptr %[[THIS_ARG:.*]], i32 %[[I_ARG:.*]])
+// LLVM:   %[[THIS_ADDR:.*]] = alloca ptr
+// LLVM:   %[[I_ADDR:.*]] = alloca i32
+// LLVM:   store ptr %[[THIS_ARG]], ptr %[[THIS_ADDR]]
+// LLVM:   store i32 %[[I_ARG]], ptr %[[I_ADDR]]
+// LLVM:   %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
+// LLVM:   store %struct.DelegatingWithZeroing zeroinitializer, ptr %[[THIS]]
+
+// Note: OGCG elides the call to the default constructor.
+
+// OGCG: define {{.*}} void @_ZN21DelegatingWithZeroingC2Ei(ptr {{.*}} %[[THIS_ARG:.*]], i32 {{.*}} %[[I_ARG:.*]])
+// OGCG:   %[[THIS_ADDR:.*]] = alloca ptr
+// OGCG:   %[[I_ADDR:.*]] = alloca i32
+// OGCG:   store ptr %[[THIS_ARG]], ptr %[[THIS_ADDR]]
+// OGCG:   store i32 %[[I_ARG]], ptr %[[I_ADDR]]
+// OGCG:   %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
+// OGCG:   call void @llvm.memset.p0.i64(ptr align 4 %[[THIS]], i8 0, i64 4, i1 false)
diff --git a/clang/test/CIR/CodeGen/new.cpp b/clang/test/CIR/CodeGen/new.cpp
@@ -23,7 +23,6 @@ void test_basic_new() {
 // CHECK:   %[[EIGHT:.*]] = cir.const #cir.int<8>
 // CHECK:   %[[NEW_S:.*]] = cir.call @_Znwm(%[[EIGHT]])
 // CHECK:   %[[NEW_S_PTR:.*]] = cir.cast(bitcast, %[[NEW_S]]
-// CHECK:   cir.call @_ZN1SC1Ev(%[[NEW_S_PTR]])
 // CHECK:   cir.store{{.*}} %[[NEW_S_PTR]], %[[PS_ADDR]]
 // CHECK:   %[[FOUR:.*]] = cir.const #cir.int<4>
 // CHECK:   %[[NEW_INT:.*]] = cir.call @_Znwm(%[[FOUR]])
@@ -40,16 +39,13 @@ void test_basic_new() {
 // LLVM:   %[[PN_ADDR:.*]] = alloca ptr, i64 1, align 8
 // LLVM:   %[[PD_ADDR:.*]] = alloca ptr, i64 1, align 8
 // LLVM:   %[[NEW_S:.*]] = call{{.*}} ptr @_Znwm(i64 8)
-// LLVM:   call{{.*}} void @_ZN1SC1Ev(ptr %[[NEW_S]])
 // LLVM:   store ptr %[[NEW_S]], ptr %[[PS_ADDR]], align 8
 // LLVM:   %[[NEW_INT:.*]] = call{{.*}} ptr @_Znwm(i64 4)
 // LLVM:   store ptr %[[NEW_INT]], ptr %[[PN_ADDR]], align 8
 // LLVM:   %[[NEW_DOUBLE:.*]] = call{{.*}} ptr @_Znwm(i64 8)
 // LLVM:   store ptr %[[NEW_DOUBLE]], ptr %[[PD_ADDR]], align 8
 // LLVM:   ret void
 
-// NOTE: OGCG elides the constructor call here, but CIR does not.
-
 // OGCG: define{{.*}} void @_Z14test_basic_newv
 // OGCG:   %[[PS_ADDR:.*]] = alloca ptr, align 8
 // OGCG:   %[[PN_ADDR:.*]] = alloca ptr, align 8
diff --git a/clang/test/CIR/CodeGen/vbase.cpp b/clang/test/CIR/CodeGen/vbase.cpp
@@ -47,28 +47,12 @@ void ppp() { B b; }
 
 // OGCG: @_ZTV1B = linkonce_odr unnamed_addr constant { [3 x ptr] } { [3 x ptr] [ptr inttoptr (i64 12 to ptr), ptr null, ptr @_ZTI1B] }, comdat, align 8
 
-// Constructor for A
-// CIR: cir.func comdat linkonce_odr @_ZN1AC2Ev(%arg0: !cir.ptr<!rec_A>
-// CIR:   %[[THIS_ADDR:.*]] = cir.alloca !cir.ptr<!rec_A>, !cir.ptr<!cir.ptr<!rec_A>>, ["this", init]
-// CIR:   cir.store %arg0, %[[THIS_ADDR]] : !cir.ptr<!rec_A>, !cir.ptr<!cir.ptr<!rec_A>>
-// CIR:   %[[THIS:.*]] = cir.load %[[THIS_ADDR]] : !cir.ptr<!cir.ptr<!rec_A>>, !cir.ptr<!rec_A>
-// CIR:   cir.return
-
-// LLVM: define{{.*}} void @_ZN1AC2Ev(ptr %[[THIS_ARG:.*]]) {
-// LLVM:   %[[THIS_ADDR:.*]] = alloca ptr
-// LLVM:   store ptr %[[THIS_ARG]], ptr %[[THIS_ADDR]]
-// LLVM:   %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
-// LLVM:   ret void
-
-// Note: OGCG elides the constructor for A. This is not yet implemented in CIR.
-
 // Constructor for B
 // CIR: cir.func comdat linkonce_odr @_ZN1BC1Ev(%arg0: !cir.ptr<!rec_B>
 // CIR:   %[[THIS_ADDR:.*]] = cir.alloca !cir.ptr<!rec_B>, !cir.ptr<!cir.ptr<!rec_B>>, ["this", init]
 // CIR:   cir.store %arg0, %[[THIS_ADDR]] : !cir.ptr<!rec_B>, !cir.ptr<!cir.ptr<!rec_B>>
 // CIR:   %[[THIS:.*]] = cir.load %[[THIS_ADDR]] : !cir.ptr<!cir.ptr<!rec_B>>, !cir.ptr<!rec_B>
 // CIR:   %[[BASE_A_ADDR:.*]] = cir.base_class_addr %[[THIS]] : !cir.ptr<!rec_B> nonnull [12] -> !cir.ptr<!rec_A>
-// CIR:   cir.call @_ZN1AC2Ev(%[[BASE_A_ADDR]]) nothrow : (!cir.ptr<!rec_A>) -> ()
 // CIR:   %[[VTABLE:.*]] = cir.vtable.address_point(@_ZTV1B, address_point = <index = 0, offset = 3>) : !cir.vptr
 // CIR:   %[[B_VPTR:.*]] = cir.vtable.get_vptr %[[THIS]] : !cir.ptr<!rec_B> -> !cir.ptr<!cir.vptr>
 // CIR:   cir.store align(8) %[[VTABLE]], %[[B_VPTR]] : !cir.vptr, !cir.ptr<!cir.vptr>
@@ -79,7 +63,6 @@ void ppp() { B b; }
 // LLVM:   store ptr %[[THIS_ARG]], ptr %[[THIS_ADDR]]
 // LLVM:   %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
 // LLVM:   %[[BASE_A_ADDR:.*]] = getelementptr i8, ptr %[[THIS]], i32 12
-// LLVM:   call void @_ZN1AC2Ev(ptr %[[BASE_A_ADDR]])
 // LLVM:   store ptr getelementptr inbounds nuw (i8, ptr @_ZTV1B, i64 24), ptr %[[THIS]]
 // LLVM:   ret void
 
@@ -90,4 +73,3 @@ void ppp() { B b; }
 // OGCG:   %[[BASE_A_ADDR:.*]] = getelementptr inbounds i8, ptr %[[THIS]], i64 12
 // OGCG:   store ptr getelementptr inbounds inrange(-24, 0) ({ [3 x ptr] }, ptr @_ZTV1B, i32 0, i32 0, i32 3), ptr %[[THIS]]
 // OGCG:   ret void
-
