https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53533
--- Comment #47 from Hongtao.liu <crazylht at gmail dot com> ---
>
> The issue is that the re-association pass doesn't handle operations
> with undefined overflow behavior, we do have duplicate bugreports
> for this.
>
I saw below in match.pd
478/* Combine successive multiplications. Similar to above, but handling
479 overflow is different. */
480(simplify
481 (mult (mult @0 INTEGER_CST@1) INTEGER_CST@2)
482 (with {
483 wi::overflow_type overflow;
484 wide_int mul = wi::mul (wi::to_wide (@1), wi::to_wide (@2),
485 TYPE_SIGN (type), &overflow);
486 }
487 /* Skip folding on overflow: the only special case is @1 * @2 ==
-INT_MIN,
488 otherwise undefined overflow implies that @0 must be zero. */
489 (if (!overflow || TYPE_OVERFLOW_WRAPS (type))
490 (mult @0 { wide_int_to_tree (type, mul); }))))
Can it be extend to (mult (plus_minus (mult @0 INTEGER_CST@1) INTEGER_CST@3)
INTEGER_CST@2), so at least we can handle it under -fwrapv?
