https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106131
Bug ID: 106131
Summary: -fstrict-aliasing breaks normal program that does not
use any pointer or reference
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: 18307130172 at fudan dot edu.cn
Target Milestone: ---
Target: x86_64-pc-linux-gnu
Created attachment 53220
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53220&action=edit
preprocessed source file
My program does not use any pointer or reference but is affected by
-fstrict-aliasing. Here is a minimal example to manifest this issue:
#include <vector>
#include <iostream>
using Pair = std::pair<int, int>;
std::vector<Pair> f = {{0, -11}, {0, -8}, {1, 2}};
int foo(Pair x, Pair y) {
return std::max(x.second, y.second);
}
int main() {
for (int J = 0; J < 1; J++) {
f[J] = f[0];
if(J == 0)
f[J] = f[2];
std::cout << foo(f[J], f[1]) << std::endl;
}
}
Save it to main.cpp and compile it with:
g++ -O2 main.cpp
The expected output should be "2", but the optimized build output "-8". If
compiled with "-O2 -fno-strict-aliasing", the output is correct.
