[Bug debug/94272] [8/9/10 Regression] -fcompare-debug failure (length) with -O -fnon-call-exceptions since r8-5241

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94272

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:5a1706f63a2024a5c2d878f2efeb8d198214542f

commit r10-7393-g5a1706f63a2024a5c2d878f2efeb8d198214542f
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Mar 26 09:18:35 2020 +0100

    c++: Fix a -fcompare-debug issue with DEBUG_BEGIN_STMT stmts in
STATEMENT_LISTs [PR94272]

    The following testcase FAILs with -fcompare-debug.  The problem is that
    the C++ FE initially uses IF_STMTs, tcc_statement which default to
    TREE_SIDE_EFFECTS set, but later on is genericized into COND_EXPRs,
    tcc_expression which default to TREE_SIDE_EFFECTS ored from all 3 operands.
    Furthermore, with -g we emit by default DEBUG_BEGIN_STMTs
(TREE_SIDE_EFFECTS
    clear) and so end up with a STATEMENT_LIST containing DEBUG_BEGIN_STMT
    + e.g. the IF_STMT, while with -g0 we would end up with just the IF_STMT
    alone and in that case there is no STATEMENT_LIST wrapping it.

    Now, the STATEMENT_LIST has TREE_SIDE_EFFECTS set to match the IF_STMT,
    but if none of the 3 operands (condition and both branches) have
    TREE_SIDE_EFFECTS, genericize_if_stmt will replace the IF_STMT with
    COND_EXPR without TREE_SIDE_EFFECTS, but with -g only STATEMENT_LIST
    wrapping it will keep TREE_SIDE_EFFECTS.  Then during gimplification,
    shortcut_cond_expr checks TREE_SIDE_EFFECTS of the operands and as it
    is differennt between -g and -g0, will generate different code.

    The following patch attempts to fix this by clearing TREE_SIDE_EFFECTS
    on STATEMENT_LISTs that initially have it set and contain only
    DEBUG_BEGIN_STMT or at most one other statement that lost TREE_SIDE_EFFECTS
    during the genericization.

    2020-03-26  Jakub Jelinek  <jakub@redhat.com>

            PR c++/94272
            * cp-gimplify.c (cp_genericize_r): Handle STATEMENT_LIST.

            * g++.dg/debug/pr94272.C: New test.