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* [Bug c++/96105] New: GCC not consistent on whether no_unique_address array is an empty data member
@ 2020-07-07 22:30 hstong at ca dot ibm.com
  2020-07-07 22:44 ` [Bug c++/96105] " dje at gcc dot gnu.org
                   ` (5 more replies)
  0 siblings, 6 replies; 7+ messages in thread
From: hstong at ca dot ibm.com @ 2020-07-07 22:30 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96105

            Bug ID: 96105
           Summary: GCC not consistent on whether no_unique_address array
                    is an empty data member
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid, rejects-valid, wrong-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hstong at ca dot ibm.com
  Target Milestone: ---

GCC treats an array marked `no_unique_address` and whose base element type is
an empty class as not an empty data member in `C` but does treat such an array
as an empty data member in `A` for the purposes of `B`. It appears that GCC's
handling of `B` is erroneous.

Compiler Explorer link: https://godbolt.org/z/XX5W3v

### SOURCE (<stdin>):
struct Empty {};

struct A {
  Empty emp [[no_unique_address]][3];
};

struct B : A {
  float f;
};

struct C {
  Empty emp [[no_unique_address]][3];
  float f;
};

extern char szc[sizeof(C)];
extern char szc[sizeof(float) * 2];  // GCC likes this
extern char szb[sizeof(B)];
extern char szb[sizeof(float) * 2];  // GCC does not like this


### COMPILER INVOCATION:
g++ -fsyntax-only -std=c++2a -Wall -Wextra -pedantic-errors -xc++ -


### ACTUAL OUTPUT:
<stdin>:19:13: error: conflicting declaration 'char szb [8]'
<stdin>:18:13: note: previous declaration as 'char szb [4]'


### EXPECTED OUTPUT:
(clean compile)


### 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/11.0.0/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 11.0.0 20200706 (experimental) (GCC)

^ permalink raw reply	[flat|nested] 7+ messages in thread
end of thread, other threads:[~2020-08-04 17:36 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-07-07 22:30 [Bug c++/96105] New: GCC not consistent on whether no_unique_address array is an empty data member hstong at ca dot ibm.com
2020-07-07 22:44 ` [Bug c++/96105] " dje at gcc dot gnu.org
2020-07-09 15:17 ` jason at gcc dot gnu.org
2020-07-09 15:19 ` jakub at gcc dot gnu.org
2020-07-10 12:36 ` cvs-commit at gcc dot gnu.org
2020-07-10 12:36 ` cvs-commit at gcc dot gnu.org
2020-08-04 17:36 ` jason at gcc dot gnu.org

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