[Bug c++/93496] New: Miscompile of range-for over braced-init-list in constructor of class with virtual inheritance

[justin.lapolla.hpe at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93496

            Bug ID: 93496
           Summary: Miscompile of range-for over braced-init-list in
                    constructor of class with virtual inheritance
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: justin.lapolla.hpe at gmail dot com
  Target Milestone: ---

Created attachment 47733
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47733&action=edit
test.ii

When I compile, link, and run the attached test.ii file, I expect the
executable to exit with status 0. Instead, it exits with status 1.

Debugging in GDB shows that the _M_len member of the braced-init-list is not
set correctly. I noticed in the assembly code that _ZN3BarC2Ev correctly sets
_M_len while _ZN3BarC1Ev does not.

Here is the correct code from _ZN3BarC2Ev:

    movl   $0x0,-0x34(%rbp) # Set braced-init-list data
    movq   $0x0,-0x30(%rbp) # Zero out _M_addr
    movq   $0x0,-0x28(%rbp) # Zero out _M_len
    movq   $0x1,-0x28(%rbp) # Set _M_len
    lea    -0x34(%rbp),%rax
    mov    %rax,-0x30(%rbp) # Set _M_addr

Here is the incorrect code from _ZN3BarC1Ev:

    movl   $0x0,-0x34(%rbp) # Set braced-init-list data
    movq   $0x0,-0x30(%rbp) # Zero out _M_addr
    movq   $0x0,-0x28(%rbp) # Zero out _M_len
                            # <MISSING> instruction to set _M_len
    lea    -0x34(%rbp),%rax
    mov    %rax,-0x30(%rbp) # Set _M_addr

Version:

---
GNU C++14 (GCC) version 8.1.0 20180502 (Cray Inc.) (x86_64-suse-linux)
        compiled by GNU C version 8.1.0 20180502 (Cray Inc.), GMP version
6.0.0, MPFR version 3.1.3, MPC version 1.0.3, isl version isl-0.15-GMP
---

System type:

---
x86_64-suse-linux
---

Configured with:

---
../cray-gcc-8.1.0-201806150759.6677a227493f2/configure
--prefix=/opt/gcc/8.1.0/snos --disable-nls --libdir=/opt/gcc/8.1.0/snos/lib
--enable-languages=c,c++,fortran
--with-gxx-include-dir=/opt/gcc/8.1.0/snos/include/g++
--with-slibdir=/opt/gcc/8.1.0/snos/lib --with-system-zlib --enable-shared
--enable-__cxa_atexit --build=x86_64-suse-linux --with-ppl --with-cloog
--disable-multilib
---

Command line that triggers the bug:

---
g++ test.ii
---

Compiler output (empty):

---
---