[Bug tree-optimization/128639] New: [14/15/16/17 Regression] wrong code at -O2: tail recursion moves a trapping division above the recursive call since r8-1042

[jeffchen006 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128639

            Bug ID: 128639
           Summary: [14/15/16/17 Regression] wrong code at -O2: tail
                    recursion moves a trapping division above the
                    recursive call since r8-1042
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jeffchen006 at gmail dot com
  Target Milestone: ---

#include <cstdio>
int z;
int f(int n, int d) {
  if (!n)
    return d ? 0 : throw 0;
  int r = f(n - 1, d);
  return r + 2 / d;
}
int main() {
  try { printf("%d\n", f(1, z)); } catch (int) { printf("caught\n"); }
}

$ g++ -O0 t.cpp && ./a.out
caught
$ g++ -O2 t.cpp && ./a.out
(no output, SIGFPE, exit 136)

Expected: caught. f(1, 0) calls f(0, 0), which throws before 2 / d runs. -O2
does the division first and gets SIGFPE.

Suspected cause: tree-tailcall: a trapping statement after the recursive call
is moved above it when the function becomes a loop (first bad 48932682a54,
2017, PR66313).

Avoided by: -fno-optimize-sibling-calls.

Known to fail: 8.5.0, 10.5.0, 11.4.0, 12.5.0, 13.4.0, 14.3.0, 15.2.0, 16.2.0,
17.0.

Known to work: 7.5.0.

-O0 -fsanitize=undefined,address is clean.

gcc version 17.0.0 20261111 (experimental) (a2a11abfad3), x86_64-pc-linux-gnu
Configured with: --enable-languages=c,c++ --disable-multilib
--disable-bootstrap --enable-checking=release