[Bug sanitizer/85213] [8 Regression] -fsanitize=undefined internal compiler error: in fold_convert_loc, at fold-const.c:2402

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85213

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #3)
> The problem is that twoval_comparison_p breaks appart SAVE_EXPR if their
> argument has no side effects.
> First, cp_build_binary_op calls save_expr on:
> (__builtin_expect ((long int) (# DEBUG BEGIN STMT;
> x != 0; ? 0 : 1), (long int) NON_LVALUE_EXPR <3>) == 0) * -1;
> and that resulting SAVE_EXPR is used in 2+ places, where one of them is a
> comparison against INTEGER_CST, which is optimized using twoval_comparison_p
> as
> another SAVE_EXPR with
> __builtin_expect ((long int) (# DEBUG BEGIN STMT;
> x != 0; ? 0 : 1), (long int) NON_LVALUE_EXPR <3>) == 0;
> body.  As mostly_copy_tree_r does not unshare STATEMENT_LISTs, we hand over
> to the gimplifier the above two SAVE_EXPRs and both contain the same
> STATEMENT_LIST, so we try to gimplify it twice, which as we know from other
> PRs doesn't really work at all.
> Now, not looking through SAVE_EXPRs in twoval_comparison_p if it contains a
> STATEMENT_LIST might result in -fcompare-debug failures, because with -g0
> there could be no STATEMENT_LIST, while with -g we have one.
> Not sure what our options are, besides just killing the SAVE_EXPR handling
> in twoval_comparison_p.

unshare the expression in twoval_comparison_p?