[Bug c++/64527] New: Constructor for empty struct not called in some situations

["gcc at swtaarrs dot com" <gcc-bugzilla@gcc.gnu.org>]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64527

            Bug ID: 64527
           Summary: Constructor for empty struct not called in some
                    situations
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc at swtaarrs dot com

Created attachment 34396
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34396&action=edit
c++ code exposing the bug

Build ctor.cpp with the following command:

> g++ -std=c++11 -Os -S -o ctor.S ctor.cpp

The optimization level doesn't appear to affect the presence of the bug, I just
used -Os to keep the output more compact.

Expected results: The m() function in ctor.S should contain a call to A::A().

Actual results: m() does nothing but zero out accessor::x. I've found at least
three ways to perturb the bug out of existence which are documented in comments
in the file.

The bug is also present in gcc 4.8.1 (I haven't tried anything older).

Compiling with -Wextra reports "warning: missing initializer for member
‘accessor::a’ [-Wmissing-field-initializers]" but I believe this shouldn't
affect the ouput.


gcc build info:

Target: x86_64-unknown-linux-gnu
Configured with: ./configure --prefix=/home/matthew/gcc-4.9.0-prefix
Thread model: posix
gcc version 4.9.0 (GCC)
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From: "zsojka at seznam dot cz" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/64528] New: [5 Regression] ICE: in process_constraint, at tree-ssa-structalias.c:3002 with -O -fno-tree-ccp -fno-tree-dce
Date: Wed, 07 Jan 2015 19:39:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd528

            Bug ID: 64528
           Summary: [5 Regression] ICE: in process_constraint, at
                    tree-ssa-structalias.c:3002 with -O -fno-tree-ccp
                    -fno-tree-dce
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz

Created attachment 34397
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id4397&actioníit
reduced testcase (from gfortran.dg/value_test.f90)

Compiler output:
$ gcc -O -fno-tree-ccp -fno-tree-dce testcase.f90
testcase.f90:11:0:

 end program valueTests
 ^
internal compiler error: in process_constraint, at tree-ssa-structalias.c:3002
0xe7907d process_constraint
        /mnt/svn/gcc-trunk/gcc/tree-ssa-structalias.c:3002
0xe793b3 process_all_all_constraints
        /mnt/svn/gcc-trunk/gcc/tree-ssa-structalias.c:3581
0xe84cd3 find_func_aliases
        /mnt/svn/gcc-trunk/gcc/tree-ssa-structalias.c:4748
0xe87c26 compute_points_to_sets
        /mnt/svn/gcc-trunk/gcc/tree-ssa-structalias.c:6825
0xe87c26 compute_may_aliases()
        /mnt/svn/gcc-trunk/gcc/tree-ssa-structalias.c:7161
0xbbd8ec execute_function_todo
        /mnt/svn/gcc-trunk/gcc/passes.c:1912
0xbbe563 execute_todo
        /mnt/svn/gcc-trunk/gcc/passes.c:1997
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.

Tested revisions:
r219277 - ICE
r218446 - ICE
r212099 - ICE
4_9 r219040 - OK