Gcc critical error

In the popular gcc compiler, and more specifically, in its optimizer, another error was detected leading to a Runtime error during program execution. When the O2 compiler option is enabled, the optimizer incorrectly processes a certain program template, which leads to fatal consequences.

Bug posted our compatriot Maxim Ivanov ( http://e-maxx.ru ), by the way, departing a month later at the ACM World Programming Championship. :)
The minimized test code looks like this:
for (int i=0; i<=1; i++)
for (int j=0; j<=1; j++) {
std::vector a[2];
a[i].push_back (0);
}



The error manifests itself if we put the local array of vectors into a double nested loop — the first attempt to write to the vector will result in a Runtime. At the same time, optimization is normal when at least one of the following conditions is met:
a) The size of the array of vectors is larger than the loop walks
b) Refer to the vector not by a [i], but through a [0], or a [1], or any other constant value
c) Before writing to a vector, execute a = std :: vector ();

It should be noted that this code is correctly compiled in Visual Studio of any version.
The error was fixed by Richard Guenther and the fix is ​​uploaded today in the gcc repository .
')
Be careful when writing programs for nuclear power plants and nuclear warheads using gcc :)

Bug report .