[Bug middle-end/79536] [5/6/7 Regression] ICE in fold_binary_loc, at fold-const.c:9060

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79536

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
The problem here is that we have a NOP_EXPR: (int) -x.  negate_expr_p returns
true for that, which means that fold_negate_expr cannot return NULL_TREE.  But
that's what happens, and that leads to a crash in fold_build2:
  581     case COMPLEX_EXPR:
  582       if (negate_expr_p (t))
  583         return fold_build2_loc (loc, COMPLEX_EXPR, type,
  584                             fold_negate_expr (loc, TREE_OPERAND (t, 0)),
  585                             fold_negate_expr (loc, TREE_OPERAND (t, 1)));

I see that negate_expr_p has STRIP_SIGN_NOPS, so the "(int) -x" becomes "-x",
but fold_negate_expr doesn't have any STRIP_SIGN_NOPS.