https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120817
Bug ID: 120817
Summary: [13/14/15 regression] Wrong code when compiled with
-O1 -ftree-loop-vectorize for AArch64 target
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: blankspruce at protonmail dot com
Target Milestone: ---
Host: x86_64-linux-gnu
Target: aarch64-linux-gnu
Build: x86_64-linux-gnu
The following code:
#include <array>
#include <cstdint>
#include <iostream>
#include <string>
auto getSafeSize(const auto inSize, const auto outSize)
{
if (inSize > outSize)
{
// Beetlejuice-like string construction
throw std::length_error("" + std::string("") + "" + std::string("") +
"" + std::string(""));
}
return std::min(inSize, outSize);
}
auto copySourceIntoTarget(const std::string& source)
{
std::array<std::uint8_t, 5> target{};
const auto loop_end = source.begin() + getSafeSize(source.size(),
target.size());
auto source_it = source.begin();
auto target_it = target.begin();
for (; source_it != loop_end; source_it++, target_it++)
{
*target_it = *source_it;
}
return target;
}
void describe(const char* name, const auto& collection)
{
std::cout << name << ": [";
for (const auto& character : collection)
{
std::cout << int(character) << ", ";
}
std::cout << "]\n";
}
int main()
{
std::string source{{'h', 'e', 'l', 'l', 'o'}};
describe("Source", source);
const auto target = copySourceIntoTarget(source);
describe("Target", target);
}
when compiled with these flags:
-mcpu=neoverse-n2+crypto -O1 -ftree-loop-vectorize -std=c++20
produces different outputs with GCC 12.2.0 and with GCC 14.2.0
GCC 12.2.0:
Source: [104, 101, 108, 108, 111, ]
Target: [104, 101, 108, 108, 111, ]
GCC 14.2.0
Source: [104, 101, 108, 108, 111, ]
Target: [0, 0, 0, 0, 0, ]
Demonstration on Godbolt: https://godbolt.org/z/75xqrW8K8
Known versions on Ubuntu affected by this problem:
Ubuntu 24.04/24.10
13.3.0-6ubuntu2
14.2.0-4ubuntu2
Ubuntu 25.04:
13.3.0-13ubuntu1
14.2.0-19ubuntu2
Based on some internal testing removal of `case IFN_MASK_STORE` seems to fix
the issue:
https://gcc.gnu.org/cgit/gcc/tree/gcc/tree-ssa-dse.cc?h=releases/gcc-14.2.0#n162
