https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103060
Bug ID: 103060
Summary: Argument initialization side-effects missing:
delegating from base constructor to inherited
constructor from virtual base
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hstong at ca dot ibm.com
Target Milestone: ---
The "only for the constructor of the most-derived class, virtual bases are
initialized" wording applies only to the non-delegating case. For a delegating
constructor, the target constructor is called even if it is inherited from a
virtual base and the constructor is not for the most-derived class.
### ONLINE COMPILER LINK:
https://godbolt.org/z/h7TnGxxv7
### SOURCE (<stdin>):
struct NonTriv {
NonTriv(int);
~NonTriv();
};
struct V { V() = default; V(NonTriv); };
struct Q { Q(); };
int bar();
struct A : virtual V, Q {
using V::V;
A() : A(bar()) { }
};
struct B : A { };
void foo() { B b; }
### COMPILER INVOCATION:
g++ -O -S -o - -xc++ -std=c++20 -
### Assembly output (snippet):
_Z3foov:
.LFB6:
.cfi_startproc
subq $24, %rsp
.cfi_def_cfa_offset 32
leaq 8(%rsp), %rdi
call _ZN1QC2Ev
addq $24, %rsp
.cfi_def_cfa_offset 8
ret
.cfi_endproc
### OBSERVATIONS:
The constructor for the direct base is being called; the wording mechanism for
that call comes from the inherited constructor invocation. That is, GCC does
invoke the inherited constructor; however, it does not process the argument.
Clang and ICC does process the argument (and also the initialization of the
corresponding parameter).
### COMPILER VERSION INFO (g++ -v):
Using built-in specs.
COLLECT_GCC=/opt/wandbox/gcc-head/bin/g++
COLLECT_LTO_WRAPPER=/opt/wandbox/gcc-head/libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../source/configure --prefix=/opt/wandbox/gcc-head
--enable-languages=c,c++ --disable-multilib --without-ppl --without-cloog-ppl
--enable-checking=release --disable-nls --enable-lto
LDFLAGS=-Wl,-rpath,/opt/wandbox/gcc-head/lib,-rpath,/opt/wandbox/gcc-head/lib64,-rpath,/opt/wandbox/gcc-head/lib32
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210721 (experimental) (GCC)
