Index: llvm/lib/Target/AVR/AVRISelLowering.cpp
===================================================================
--- llvm/lib/Target/AVR/AVRISelLowering.cpp
+++ llvm/lib/Target/AVR/AVRISelLowering.cpp
@@ -1285,8 +1285,8 @@
   const Function *F = nullptr;
   if (const GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
     const GlobalValue *GV = G->getGlobal();
-
-    F = cast<Function>(GV);
+    if (isa<Function>(GV))
+      F = cast<Function>(GV);
     Callee =
         DAG.getTargetGlobalAddress(GV, DL, getPointerTy(DAG.getDataLayout()));
   } else if (const ExternalSymbolSDNode *ES =
Index: llvm/test/CodeGen/AVR/issue-43443-ctor-alias.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AVR/issue-43443-ctor-alias.ll
@@ -0,0 +1,71 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=avr -O0 -verify-machineinstrs | FileCheck %s
+
+; This .ll file is generated from the following cpp program:
+; struct foo {
+;   foo();
+; };
+; foo::foo() {}
+; foo f2;
+; Check https://github.com/llvm/llvm-project/issues/43443 for details.
+
+%struct.foo = type { i8 }
+
+@f2 = global %struct.foo zeroinitializer
+
+@llvm.global_ctors = appending global [1 x { i32, void () addrspace(1)*, i8* }] [{ i32, void () addrspace(1)*, i8* } { i32 65535, void () addrspace(1)* @_GLOBAL__sub_I_failed.cc, i8* null }]
+
+@_ZN3fooC1Ev = alias void (%struct.foo*), void (%struct.foo*) addrspace(1)* @_ZN3fooC2Ev
+
+define void @_ZN3fooC2Ev(%struct.foo* dereferenceable(1) %this) {
+; CHECK-LABEL: _ZN3fooC2Ev:
+; CHECK:       ; %bb.0: ; %entry
+; CHECK-NEXT:    push r28
+; CHECK-NEXT:    push r29
+; CHECK-NEXT:    in r28, 61
+; CHECK-NEXT:    in r29, 62
+; CHECK-NEXT:    sbiw r28, 2
+; CHECK-NEXT:    in r0, 63
+; CHECK-NEXT:    cli
+; CHECK-NEXT:    out 62, r29
+; CHECK-NEXT:    out 63, r0
+; CHECK-NEXT:    out 61, r28
+; CHECK-NEXT:    std Y+1, r24
+; CHECK-NEXT:    std Y+2, r25
+; CHECK-NEXT:    adiw r28, 2
+; CHECK-NEXT:    in r0, 63
+; CHECK-NEXT:    cli
+; CHECK-NEXT:    out 62, r29
+; CHECK-NEXT:    out 63, r0
+; CHECK-NEXT:    out 61, r28
+; CHECK-NEXT:    pop r29
+; CHECK-NEXT:    pop r28
+; CHECK-NEXT:    ret
+entry:
+  %this.addr = alloca %struct.foo*
+  store %struct.foo* %this, %struct.foo** %this.addr
+  %this1 = load %struct.foo*, %struct.foo** %this.addr
+  ret void
+}
+
+define internal void @__cxx_global_var_init() addrspace(1) {
+; CHECK-LABEL: __cxx_global_var_init:
+; CHECK:       ; %bb.0: ; %entry
+; CHECK-NEXT:    ldi r24, lo8(f2)
+; CHECK-NEXT:    ldi r25, hi8(f2)
+; CHECK-NEXT:    call _ZN3fooC1Ev
+; CHECK-NEXT:    ret
+entry:
+  call addrspace(1) void @_ZN3fooC1Ev(%struct.foo* dereferenceable(1) @f2)
+  ret void
+}
+
+define internal void @_GLOBAL__sub_I_failed.cc() addrspace(1) {
+; CHECK-LABEL: _GLOBAL__sub_I_failed.cc:
+; CHECK:       ; %bb.0: ; %entry
+; CHECK-NEXT:    call __cxx_global_var_init
+; CHECK-NEXT:    ret
+entry:
+  call addrspace(1) void @__cxx_global_var_init()
+  ret void
+}