https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108342
Bug ID: 108342
Summary: std::complex: ignoring packed attribute because of
unpacked non-POD field
Product: gcc
Version: 12.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ruilvo at ua dot pt
Target Milestone: ---
Created attachment 54217
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54217&action=edit
Code to reproduce the bug report
Summary:
With the annexed code, reproduced on the following CE link:
https://godbolt.org/z/1q9a5Mq7r
I get the following warning:
```
<source>:29:16: warning: ignoring packed attribute because of unpacked non-POD
field 'fcomplex_t <unnamed struct>::bb_iq_samples [512]'
29 | fcomplex_t bb_iq_samples[BB_FRAME_IQ_SAMPLES_COUNT];
| ^~~~~~~~~~~~~
```
Clang doesn't complain facing the same code.
Details:
I was trying to write a C++ library, which is going to target an ARM Linux
system, but leaving C-compatible "bindings" and structs for using with CFFI on
other languages.
The library deals with a serial stream that I don't control, and that I wanted
to de-serialize, thus the weird structure.
I discovered the problem (warning) when I changed from a C source file and
`_Complex float` to C++ and `std::complex<float>`.
The compiler I first discovered the problem on was arm-linux-gnueabihf-g++
(GCC) 12.2.1 20221203 [releases/gcc-12 revision
c03cb4b762aceeba95da918b042583af0d9f6030] from Linaro.
The bug is reproducible on x86 and mainline GCC (see Compiler Explorer URL)
Expected behaviour:
For this code to compile without warnings and producing the desired effect
(packing). The C++ standard even carves out a guarantee than `_Complex
[float|double]` is memory-layout-compatible with
`std::complex<[float|double]>`.
