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

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

[zsojka at seznam dot cz]

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

            Bug ID: 94272
           Summary: [8/9/10 Regression] -fcompare-debug failure (length)
                    with -O -fnon-call-exceptions
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
                CC: aoliva at gcc dot gnu.org
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu

Created attachment 48084
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48084&action=edit
reduced testcase

Compiler output:
$ x86_64-pc-linux-gnu-g++ -O -fnon-call-exceptions -fcompare-debug testcase.C
x86_64-pc-linux-gnu-g++: error: testcase.C: '-fcompare-debug' failure (length)

$ x86_64-pc-linux-gnu-g++ -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-g++
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-r10-7327-20200323085706-g2fa4b1ffd6e-checking-yes-rtl-df-extra-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/10.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--with-cloog --with-ppl --with-isl --build=x86_64-pc-linux-gnu
--host=x86_64-pc-linux-gnu --target=x86_64-pc-linux-gnu
--with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-r10-7327-20200323085706-g2fa4b1ffd6e-checking-yes-rtl-df-extra-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.0.1 20200323 (experimental) (GCC)

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

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
            Summary|[8/9/10 Regression]         |[8/9/10 Regression]
                   |-fcompare-debug failure     |-fcompare-debug failure
                   |(length) with -O            |(length) with -O
                   |-fnon-call-exceptions       |-fnon-call-exceptions since
                   |                            |r8-5241
     Ever confirmed|0                           |1
                 CC|                            |jakub at gcc dot gnu.org
   Last reconfirmed|                            |2020-03-23
   Target Milestone|---                         |8.5

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r8-5241-g8697bf9f46f36168ddba5752db582e673e3cbe8c.  I'll have a
look.

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

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
           Assignee|jakub at gcc dot gnu.org           |unassigned at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I'm afraid this is similar to the PR93786 and I don't have a good solution.
This goes wrong during gimplification, we have:
if (c != 0B && d != 0)
  {
    (void) 0;
  }
else
  {
    # DEBUG BEGIN STMT;
    if (*e != 0) (void) 0;
  }
When we call shortcut_cond_expr, the important difference is that without -g,
TREE_SIDE_EFFECTS on else_ (which is in that case a COND_EXPR) is false, but
with -g it is true (else_ is a STATEMENT_LIST with TREE_SIDE_EFFECTS set
containing the DEBUG_BEGIN_STMT with TREE_SIDE_EFFECTS false and the COND_EXPR
also with TREE_SIDE_EFFECTS clear.

Alex?

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

[jakub at gcc dot gnu.org]

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

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think another reason why this FAILs is that the IF_STMTs that the FE emits
initially have TREE_SIDE_EFFECTS set, because those are tcc_statement and for
those make_node sets TREE_SIDE_EFFECTS.  While genericize_if_stmt genericizes
that into a COND_EXPR, which is tcc_expression and thus has TREE_SIDE_EFFECTS
computed from TREE_SIDE_EFFECTS of the 3 operands (none of them have that set).

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

[jakub at gcc dot gnu.org]

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

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 48090
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48090&action=edit
gcc10-pr94272.patch

Untested hack (admittedly quite ugly) that seems to fix this testcase.

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

[rguenth at gcc dot gnu.org]

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

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[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]

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.

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

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org
            Summary|[8/9/10 Regression]         |[8/9 Regression]
                   |-fcompare-debug failure     |-fcompare-debug failure
                   |(length) with -O            |(length) with -O
                   |-fnon-call-exceptions since |-fnon-call-exceptions since
                   |r8-5241                     |r8-5241
             Status|NEW                         |ASSIGNED

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed on the trunk so far.

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

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|8.5                         |9.4

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.

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

[rguenth at gcc dot gnu.org]

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

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

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

[rguenth at gcc dot gnu.org]

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

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED
   Target Milestone|9.5                         |10.0

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed in GCC 10.