https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118726
Bug ID: 118726
Summary: GCC generates wrong code when using non-structured
binding declaration as the condition of a for-loop at
O2 level
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: xiaohuba2021 at 163 dot com
Target Milestone: ---
The following code:
```
#include <iostream>
int main() {
volatile int x = 10;
for (int l = 1; int d = x - l; x = d + 1) {
int &z = d;
std::cout << z << '\n';
}
}
```
continues to output `9` and crashes on trunk, with `-O2` enabled, while clang
works properly.
godbolt: https://godbolt.org/z/1nx6fvo1M
compiler version:
```
Using built-in specs.
COLLECT_GCC=/opt/compiler-explorer/gcc-snapshot/bin/g++
Target: x86_64-linux-gnu
Configured with: ../gcc-trunk-20250201/configure
--prefix=/opt/compiler-explorer/gcc-build/staging
--enable-libstdcxx-backtrace=yes --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu --disable-bootstrap
--enable-multiarch --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --enable-clocale=gnu
--enable-languages=c,c++,fortran,ada,objc,obj-c++,go,d,rust,m2 --enable-ld=yes
--enable-gold=yes --enable-libstdcxx-debug --enable-libstdcxx-time=yes
--enable-linker-build-id --enable-lto --enable-plugins --enable-threads=posix
--with-pkgversion=Compiler-Explorer-Build-gcc-d3ba88308426b3db55793831b0ae8c760aad9de7-binutils-2.42
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 15.0.1 20250201 (experimental)
(Compiler-Explorer-Build-gcc-d3ba88308426b3db55793831b0ae8c760aad9de7-binutils-2.42)
COLLECT_GCC_OPTIONS='-fdiagnostics-color=always' '-g' '-o' '/app/output.s'
'-masm=intel' '-fno-verbose-asm' '-S' '-O2' '-Wall' '-Wextra' '-v'
'-shared-libgcc' '-mtune=generic' '-march=x86-64' '-dumpdir' '/app/'
/opt/compiler-explorer/gcc-trunk-20250201/bin/../libexec/gcc/x86_64-linux-gnu/15.0.1/cc1plus
-quiet -v -imultiarch x86_64-linux-gnu -iprefix
/opt/compiler-explorer/gcc-trunk-20250201/bin/../lib/gcc/x86_64-linux-gnu/15.0.1/
-D_GNU_SOURCE <source> -quiet -dumpdir /app/ -dumpbase output.cpp -dumpbase-ext
.cpp -masm=intel -mtune=generic -march=x86-64 -g -O2 -Wall -Wextra -version
-fdiagnostics-color=always -fno-verbose-asm -o /app/output.s
GNU C++17
(Compiler-Explorer-Build-gcc-d3ba88308426b3db55793831b0ae8c760aad9de7-binutils-2.42)
version 15.0.1 20250201 (experimental) (x86_64-linux-gnu)
compiled by GNU C version 11.4.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
```
