https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113676
Bug ID: 113676
Summary: Miscompilation tree-vrp __builtin_unreachable
Product: gcc
Version: 12.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: magnus.hegdahl at gmail dot com
Target Milestone: ---
Compiling the following code with -O1 -ftree-vrp or higher on GCC 10 or 12
results in a program that segfaults when argc >= 2.
#include <bit>
#include <vector>
auto main(int argc, char **) -> int {
auto rounded_n = std::bit_ceil(static_cast<unsigned>(argc));
auto a = std::vector<int>(2UL * rounded_n);
for (std::size_t i = rounded_n; i-- > 1;) {
if (!(0 < i && i < rounded_n)) __builtin_unreachable();
a[i] = 0;
}
}
If __builtin_unreachable is replaced by for example __builtin_trap, there is no
bug.
I could not reproduce this in GCC 11 or 13.
https://godbolt.org/z/dvEWKzWTh
Disassembly of the loop body:
.L6:
mov DWORD PTR [rdi+rdx*4], 0
sub rdx, 1
jmp .L6
