[Bug tree-optimization/108366] [12/13 Regression] Spurious stringop overflow, possibly alias-related

["BenWiederhake.GitHub at gmx dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108366

--- Comment #1 from Ben Wiederhake <BenWiederhake.GitHub at gmx dot de> ---
Preprocessed file see attachments, and output as generated by -v -save-temps
here:

$ g++ -v -o foo -O2 -std=c++20 -save-temps repro.cpp 
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/12/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 12.2.0-13'
--with-bugurl=file:///usr/share/doc/gcc-12/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-12
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --enable-libphobos-checking=release
--with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch
--disable-werror --enable-cet --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-12-PBog5r/gcc-12-12.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-12-PBog5r/gcc-12-12.2.0/debian/tmp-gcn/usr
--enable-offload-defaulted --without-cuda-driver --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.2.0 (Debian 12.2.0-13) 
COLLECT_GCC_OPTIONS='-v' '-o' 'foo' '-O2' '-std=c++20' '-save-temps'
'-shared-libgcc' '-mtune=generic' '-march=x86-64' '-dumpdir' 'foo-'
 /usr/lib/gcc/x86_64-linux-gnu/12/cc1plus -E -quiet -v -imultiarch
x86_64-linux-gnu -D_GNU_SOURCE repro.cpp -mtune=generic -march=x86-64
-std=c++20 -O2 -fpch-preprocess -fasynchronous-unwind-tables -o foo-repro.ii
ignoring duplicate directory "/usr/include/x86_64-linux-gnu/c++/12"
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/12/include-fixed"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/12
 /usr/include/x86_64-linux-gnu/c++/12
 /usr/include/c++/12/backward
 /usr/lib/gcc/x86_64-linux-gnu/12/include
 /usr/local/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-o' 'foo' '-O2' '-std=c++20' '-save-temps'
'-shared-libgcc' '-mtune=generic' '-march=x86-64' '-dumpdir' 'foo-'
 /usr/lib/gcc/x86_64-linux-gnu/12/cc1plus -fpreprocessed foo-repro.ii -quiet
-dumpdir foo- -dumpbase repro.cpp -dumpbase-ext .cpp -mtune=generic
-march=x86-64 -O2 -std=c++20 -version -fasynchronous-unwind-tables -o
foo-repro.s
GNU C++20 (Debian 12.2.0-13) version 12.2.0 (x86_64-linux-gnu)
        compiled by GNU C version 12.2.0, GMP version 6.2.1, MPFR version
4.1.1-p1, MPC version 1.3.1, isl version isl-0.25-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++20 (Debian 12.2.0-13) version 12.2.0 (x86_64-linux-gnu)
        compiled by GNU C version 12.2.0, GMP version 6.2.1, MPFR version
4.1.1-p1, MPC version 1.3.1, isl version isl-0.25-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: b9e5387ca128f541a98a8ca5afd00294
In function ‘Vector make_vector()’,
    inlined from ‘int main()’ at repro.cpp:36:31:
repro.cpp:27:11: warning: ‘void* memset(void*, int, size_t)’ writing 128 bytes
into a region of size 40 overflows the destination [-Wstringop-overflow=]
   27 |     memset(buffer.data(), 'A', new_size);
      |     ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
repro.cpp: In function ‘int main()’:
repro.cpp:36:10: note: destination object ‘actual’ of size 40
   36 |     auto actual = make_vector();
      |          ^~~~~~
COLLECT_GCC_OPTIONS='-v' '-o' 'foo' '-O2' '-std=c++20' '-save-temps'
'-shared-libgcc' '-mtune=generic' '-march=x86-64' '-dumpdir' 'foo-'
 as -v --64 -o foo-repro.o foo-repro.s
GNU assembler version 2.39.90 (x86_64-linux-gnu) using BFD version (GNU
Binutils for Debian) 2.39.90.20230104
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/12/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/12/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-o' 'foo' '-O2' '-std=c++20' '-save-temps'
'-shared-libgcc' '-mtune=generic' '-march=x86-64' '-dumpdir' 'foo.'
 /usr/lib/gcc/x86_64-linux-gnu/12/collect2 -plugin
/usr/lib/gcc/x86_64-linux-gnu/12/liblto_plugin.so
-plugin-opt=/usr/lib/gcc/x86_64-linux-gnu/12/lto-wrapper
-plugin-opt=-fresolution=foo.res -plugin-opt=-pass-through=-lgcc_s
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --build-id
--eh-frame-hdr -m elf_x86_64 --hash-style=gnu --as-needed -dynamic-linker
/lib64/ld-linux-x86-64.so.2 -pie -o foo
/usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/Scrt1.o
/usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/crti.o
/usr/lib/gcc/x86_64-linux-gnu/12/crtbeginS.o -L/usr/lib/gcc/x86_64-linux-gnu/12
-L/usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu
-L/usr/lib/gcc/x86_64-linux-gnu/12/../../../../lib -L/lib/x86_64-linux-gnu
-L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib
-L/usr/lib/gcc/x86_64-linux-gnu/12/../../.. foo-repro.o -lstdc++ -lm -lgcc_s
-lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-linux-gnu/12/crtendS.o
/usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/crtn.o
COLLECT_GCC_OPTIONS='-v' '-o' 'foo' '-O2' '-std=c++20' '-save-temps'
'-shared-libgcc' '-mtune=generic' '-march=x86-64' '-dumpdir' 'foo.'