[Bug tree-optimization/110652] New: [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[Bug tree-optimization/110652] New: [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

            Bug ID: 110652
           Summary: [14 Regression] bootstrap failure on
                    tree-vect-stmts.cc with  --enable-checking=release:
                    error: 'new_temp' may be used uninitialized
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Noticed build failure today when built r14-2495-g43ed05a08963a5 as:

$ ~/dev/git/gcc/configure --disable-multilib --enable-checking=release
$ make
...
/tmp/gb/./prev-gcc/xg++ -B/tmp/gb/./prev-gcc/
-B/usr/local/x86_64-pc-linux-gnu/bin/ -nostdinc++
-B/tmp/gb/prev-x86_64-pc-linux-gnu/libstdc++-v3/src/.libs
-B/tmp/gb/prev-x86_64-pc-linux-gnu/libstdc++-v3/libsupc++/.libs 
-I/tmp/gb/prev-x86_64-pc-linux-gnu/libstdc++-v3/include/x86_64-pc-linux-gnu 
-I/tmp/gb/prev-x86_64-pc-linux-gnu/libstdc++-v3/include 
-I/home/slyfox/dev/git/gcc/libstdc++-v3/libsupc++
-L/tmp/gb/prev-x86_64-pc-linux-gnu/libstdc++-v3/src/.libs
-L/tmp/gb/prev-x86_64-pc-linux-gnu/libstdc++-v3/libsupc++/.libs  -fno-PIE -c  
-g -O2 -fno-checking -gtoggle -DIN_GCC    -fno-exceptions -fno-rtti
-fasynchronous-unwind-tables -W -Wall -Wno-narrowing -Wwrite-strings
-Wcast-qual -Wmissing-format-attribute -Wconditionally-supported
-Woverloaded-virtual -pedantic -Wno-long-long -Wno-variadic-macros
-Wno-overlength-strings -Werror   -DHAVE_CONFIG_H -fno-PIE -I. -I.
-I/home/slyfox/dev/git/gcc/gcc -I/home/slyfox/dev/git/gcc/gcc/.
-I/home/slyfox/dev/git/gcc/gcc/../include 
-I/home/slyfox/dev/git/gcc/gcc/../libcpp/include
-I/home/slyfox/dev/git/gcc/gcc/../libcody 
-I/home/slyfox/dev/git/gcc/gcc/../libdecnumber
-I/home/slyfox/dev/git/gcc/gcc/../libdecnumber/bid -I../libdecnumber
-I/home/slyfox/dev/git/gcc/gcc/../libbacktrace   -o tree-vect-stmts.o -MT
tree-vect-stmts.o -MMD -MP -MF ./.deps/tree-vect-stmts.TPo
/home/slyfox/dev/git/gcc/gcc/tree-vect-stmts.cc
In file included from /home/slyfox/dev/git/gcc/gcc/hash-table.h:248,
                 from /home/slyfox/dev/git/gcc/gcc/coretypes.h:486,
                 from /home/slyfox/dev/git/gcc/gcc/tree-vect-stmts.cc:24:
In member function 'T* vec<T, A, vl_embed>::quick_push(const T&) [with T =
tree_node*; A = va_heap]',
    inlined from 'T* vec<T>::quick_push(const T&) [with T = tree_node*]' at
/home/slyfox/dev/git/gcc/gcc/vec.h:1987:28,
    inlined from 'bool vectorizable_load(vec_info*, stmt_vec_info,
gimple_stmt_iterator*, gimple**, slp_tree, stmt_vector_for_cost*)' at
/home/slyfox/dev/git/gcc/gcc/tree-vect-stmts.cc:10962:23:
/home/slyfox/dev/git/gcc/gcc/vec.h:1023:9: error: 'new_temp' may be used
uninitialized [-Werror=maybe-uninitialized]
 1023 |   *slot = obj;
      |   ~~~~~~^~~~~

$ /tmp/gb/./prev-gcc/xg++ -B/tmp/gb/./prev-gcc/ -v
Reading specs from /tmp/gb/./prev-gcc/specs
COLLECT_GCC=/tmp/gb/./prev-gcc/xg++
COLLECT_LTO_WRAPPER=/tmp/gb/./prev-gcc/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /home/slyfox/dev/git/gcc/configure --disable-multilib
--enable-checking=release
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20230713 (experimental) (GCC)

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0
           Keywords|                            |build, diagnostic

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
new_temp does look like it is initialized on the !costing_p path too ..

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

Sergei Trofimovich <slyfox at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |linkw at gcc dot gnu.org

--- Comment #2 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
If it helps bisect landed on r14-2493-g5f03844b32f452

commit 5f03844b32f45224c33dcea08a20b5a2089082f7
Author: Kewen Lin <linkw@linux.ibm.com>
Date:   Wed Jul 12 21:23:22 2023 -0500

    vect: Adjust vectorizable_load costing on VMAT_CONTIGUOUS_REVERSE

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-07-14
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #3 from Kewen Lin <linkw at gcc dot gnu.org> ---
Thanks for reporting and I'll have a look.

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

--- Comment #4 from Kewen Lin <linkw at gcc dot gnu.org> ---
I can't reproduce this on ppc64le with both the default bootstrapping checking
option --enable-checking=yes,extra and the reported --enable-checking=release.
I'm going to test it on cfarm x86 machine.

If the error message lineno is correct, it complains on line 10962:

              /* Collect vector loads and later create their permutation in
                 vect_transform_grouped_load ().  */
              if (!costing_p && (grouped_load || slp_perm))
                dr_chain.quick_push (new_temp); // line 10962

It's guarded with !costing_p and we have:

              /* One common place to cost the above vect load for different
                 alignment support schemes.  */
              if (costing_p)
                {
                 ...
                }
              else
                {
                  vec_dest = vect_create_destination_var (scalar_dest,
vectype);
                  ...
                  new_temp = make_ssa_name (vec_dest, new_stmt);  // line 10911
                  ...
                }

at line 10911, new_temp is always initialized for !costing_p. It looks like a
false positive.

Anyway, I'll reproduce it first on x86.

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #5 from Kewen Lin <linkw at gcc dot gnu.org> ---
I can reproduce this on cfarm x86 machine, the complained line is exactly the
one in comment #c4, I believe it's a false positive.

How do we work around this normally?  Just initializing new_temp with NULL_TREE
as below?

diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index c08d0ef951f..124caab5c1f 100644
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -9297,7 +9297,7 @@ vectorizable_load (vec_info *vinfo,
   class loop *containing_loop = gimple_bb (stmt_info->stmt)->loop_father;
   bool nested_in_vect_loop = false;
   tree elem_type;
-  tree new_temp;
+  tree new_temp = NULL_TREE;
   machine_mode mode;
   tree dummy;
   tree dataref_ptr = NULL_TREE;

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

--- Comment #6 from rguenther at suse dot de <rguenther at suse dot de> ---
On Fri, 14 Jul 2023, linkw at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652
> 
> Kewen Lin <linkw at gcc dot gnu.org> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>                  CC|                            |rguenth at gcc dot gnu.org
> 
> --- Comment #5 from Kewen Lin <linkw at gcc dot gnu.org> ---
> I can reproduce this on cfarm x86 machine, the complained line is exactly the
> one in comment #c4, I believe it's a false positive.
> 
> How do we work around this normally?  Just initializing new_temp with NULL_TREE
> as below?

Yes, possibly with a comment refering to this PR.

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |danglin at gcc dot gnu.org

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 110672 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Kewen Lin <linkw@gcc.gnu.org>:

https://gcc.gnu.org/g:081c623ca88dc53abe34b5f5661e79fcde800cef

commit r14-2560-g081c623ca88dc53abe34b5f5661e79fcde800cef
Author: Kewen Lin <linkw@linux.ibm.com>
Date:   Mon Jul 17 03:44:59 2023 -0500

    vect: Initialize new_temp to avoid false positive warning [PR110652]

    As PR110652 and its duplicate PRs show, there could be one
    build error

      error: 'new_temp' may be used uninitialized

    for some build configurations.  It's a false positive warning
    (or error at -Werror), but in order to make the build succeed,
    this patch is to initialize the reported variable 'new_temp'
    as NULL_TREE.

            PR tree-optimization/110652

    gcc/ChangeLog:

            * tree-vect-stmts.cc (vectorizable_load): Initialize new_temp as
            NULL_TREE.

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

Kewen Lin <linkw at gcc dot gnu.org> changed:

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

--- Comment #9 from Kewen Lin <linkw at gcc dot gnu.org> ---
Should be fixed on trunk.

[Bug tree-optimization/110652] [14 Regression] bootstrap failure on tree-vect-stmts.cc with --enable-checking=release: error: 'new_temp' may be used uninitialized

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110652

--- Comment #10 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
I confirm the change fixed build for me (it also needed unrelated workaround
for https://gcc.gnu.org/PR110697). Thank you!