[Bug middle-end/104092] New: [12 Regression] Invalid -Wdangling-pointer warning after writes by calls

[Bug middle-end/104092] New: [12 Regression] Invalid -Wdangling-pointer warning after writes by calls

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104092

            Bug ID: 104092
           Summary: [12 Regression] Invalid -Wdangling-pointer warning
                    after writes by calls
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rsandifo at gcc dot gnu.org
  Target Milestone: ---

Compiling the following testcase with -march=armv8.2-a+sve -O2 -Wall:

--------------------------------------------------------------------
#include <arm_sve.h>

svuint64_t bar(svbool_t pg, const uint64_t *addr) {
  return svget2(svld2_u64(pg, addr), 0);
}
--------------------------------------------------------------------

triggers:

foo.c:4:16: warning: using a dangling pointer to an unnamed temporary
[-Wdangling-pointer=]
    4 |   return svget2(svld2_u64(pg, addr), 0);
      |          ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
foo.c:4:16: note: unnamed temporary defined here
    4 |   return svget2(svld2_u64(pg, addr), 0);
      |          ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

This is because the code looks only at gassigns when tracking whether
a clobber has been overwritten, so it misses assignments by calls.

This seems to be different from PR104076.

[Bug middle-end/104092] [12 Regression] Invalid -Wdangling-pointer warning after writes by calls

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104092

rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |rsandifo at gcc dot gnu.org
   Last reconfirmed|                            |2022-01-18

--- Comment #1 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
Testing a patch.

[Bug middle-end/104092] [12 Regression] Invalid -Wdangling-pointer warning after writes by calls

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104092

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0
           Keywords|                            |diagnostic

[Bug middle-end/104092] [12 Regression] Invalid -Wdangling-pointer warning after writes by calls

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104092

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:551aa75778a4c5165d9533cd447c8fc822f583e1

commit r12-7044-g551aa75778a4c5165d9533cd447c8fc822f583e1
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Feb 2 14:24:39 2022 +0100

    Add CLOBBER_EOL to mark storage end-of-life clobbers

    This adds a flag to CONSTRUCTOR nodes indicating that for
    clobbers this marks the end-of-life of storage as opposed to
    just ending the lifetime of the object that occupied it.
    The dangling pointer diagnostics uses CLOBBERs but is confused
    by those emitted by the C++ frontend for example which emits
    them for the second purpose at the start of CTORs.  The issue
    is also appearant for aarch64 in PR104092.

    Distinguishing the two cases is also necessary for the PR90348 fix.

    Since I'm going to add another flag I added an enum clobber_flags
    and a defaulted argument to build_clobber plus a convenient way to
    query the enum from the CTOR tree and specify it for gimple_clobber_p.
    Since 'CLOBBER' is already taken and I needed a name for the unspecified
    clobber we have now I used 'CLOBBER_UNDEF'.

    2022-02-03  Richard Biener  <rguenther@suse.de>

            PR middle-end/90348
            PR middle-end/104092
    gcc/
            * tree-core.h (clobber_kind): New enum.
            (tree_base::u::bits::address_space): Document use in CONSTRUCTORs.
            * tree.h (CLOBBER_KIND): Add.
            (build_clobber): Add clobber kind argument, defaulted to
            CLOBBER_UNDEF.
            * tree.cc (build_clobber): Likewise.
            * gimple.h (gimple_clobber_p): New overload with specified kind.
            * tree-streamer-in.cc (streamer_read_tree_bitfields): Stream
            CLOBBER_KIND.
            * tree-streamer-out.cc (streamer_write_tree_bitfields):
            Likewise.
            * tree-pretty-print.cc (dump_generic_node): Mark EOL CLOBBERs.
            * gimplify.cc (gimplify_bind_expr): Build storage end-of-life
clobbers
            with CLOBBER_EOL.
            (gimplify_target_expr): Likewise.
            * tree-inline.cc (expand_call_inline): Likewise.
            * tree-ssa-ccp.cc (insert_clobber_before_stack_restore): Likewise.
            * gimple-ssa-warn-access.cc (pass_waccess::check_stmt): Only treat
            CLOBBER_EOL clobbers as ending lifetime of storage.

    gcc/lto/
            * lto-common.cc (compare_tree_sccs_1): Compare CLOBBER_KIND.

    gcc/testsuite/
            * gcc.dg/pr87052.c: Adjust.

[Bug middle-end/104092] [12 Regression] Invalid -Wdangling-pointer warning after writes by calls

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104092

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Should be fixed now.

[Bug middle-end/104092] [12 Regression] Invalid -Wdangling-pointer warning after writes by calls

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104092

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Richard Sandiford <rsandifo@gcc.gnu.org>:

https://gcc.gnu.org/g:5b6370295d1efaa563f6d8c45f1fb779c3db452e

commit r12-7045-g5b6370295d1efaa563f6d8c45f1fb779c3db452e
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Fri Feb 4 08:08:59 2022 +0000

    aarch64: Add test for PR104092

    gcc/testsuite/
            PR middle-end/104092
            * gcc.target/aarch64/sve/acle/general/pr104092.c: New test.