[Bug tree-optimization/81900] New: GCC trunk miscompiles Perl / __sigsetjmp issue

[pipcet at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81900

            Bug ID: 81900
           Summary: GCC trunk miscompiles Perl / __sigsetjmp issue
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pipcet at gmail dot com
  Target Milestone: ---

Created attachment 42007
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42007&action=edit
creduce-minimized test case

Hi,

I'm having trouble running a GCC/trunk-compiled Perl; I first noticed
the problem on my WebAssembly port, but I think I can reproduce it on
x86_64 built from the standard GCC tree. I also think this is a GCC
bug.

After some editing, I've managed to generate a (somewhat) minimized
testcase:

Perl_croak() __attribute__((noreturn));
*Perl_sv_gets();
a() {
  __sigsetjmp();
  char *b;
  if ((b = Perl_sv_gets()) == 0)
    Perl_croak("No Perl script found in input\n");
  if (*b == '#')
    __asm__("" : : ""("badbad"));
}

The intended behaviour is that Perl_sv_gets() can return a NULL
pointer, in which case the pointer isn't dereferenced and Perl_croak()
is called instead.  However, the assembly output I get is:

        xorl    %eax, %eax
        call    __sigsetjmp
        xorl    %eax, %eax
        call    Perl_sv_gets
        cmpb    $35, (%rax)

The call to Perl_croak has been removed, and the return value of
Perl_sv_gets() is unconditionally dereferenced.  That's wrong, right?

I'm compiling with:

$ ~/git/asmjs/subrepos/gcc/host-x86_64-pc-linux-gnu/gcc/xgcc -B
/home/pip/git/asmjs/subrepos/gcc/host-x86_64-pc-linux-gnu/gcc/ -v -S
-DPERL_CORE -fwrapv -std=c89 -O3 -fno-strict-aliasing -w -Wfatal-errors
testcase.i -o tmp.s || exit 1
Reading specs from
/home/pip/git/asmjs/subrepos/gcc/host-x86_64-pc-linux-gnu/gcc/specs
COLLECT_GCC=/home/pip/git/asmjs/subrepos/gcc/host-x86_64-pc-linux-gnu/gcc/xgcc
Target: x86_64-pc-linux-gnu
Configured with: ./configure --target=x86_64-pc-linux-gnu --disable-bootstrap
--enable-languages=c
Thread model: posix
gcc version 8.0.0 20170819 (experimental) (GCC) 
COLLECT_GCC_OPTIONS='-B'
'/home/pip/git/asmjs/subrepos/gcc/host-x86_64-pc-linux-gnu/gcc/' '-v' '-S' '-D'
'PERL_CORE' '-fwrapv' '-std=c90' '-O3' '-fno-strict-aliasing' '-w'
'-Wfatal-errors' '-o' 'tmp.s' '-mtune=generic' '-march=x86-64'
 /home/pip/git/asmjs/subrepos/gcc/host-x86_64-pc-linux-gnu/gcc/cc1
-fpreprocessed testcase.i -quiet -dumpbase testcase.i -mtune=generic
-march=x86-64 -auxbase-strip tmp.s -O3 -Wfatal-errors -w -std=c90 -version
-fwrapv -fno-strict-aliasing -o tmp.s
GNU C89 (GCC) version 8.0.0 20170819 (experimental) (x86_64-pc-linux-gnu)
        compiled by GNU C version 6.4.0 20170724, GMP version 6.1.2, MPFR
version 3.1.5, MPC version 1.0.3, isl version none
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
GNU C89 (GCC) version 8.0.0 20170819 (experimental) (x86_64-pc-linux-gnu)
        compiled by GNU C version 6.4.0 20170724, GMP version 6.1.2, MPFR
version 3.1.5, MPC version 1.0.3, isl version none
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: d531daafd687d9500452e3b103d32887
COMPILER_PATH=/home/pip/git/asmjs/subrepos/gcc/host-x86_64-pc-linux-gnu/gcc/
LIBRARY_PATH=/home/pip/git/asmjs/subrepos/gcc/host-x86_64-pc-linux-gnu/gcc/:/lib/x86_64-linux-gnu/:/lib/../lib64/:/usr/lib/x86_64-linux-gnu/:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-B'
'/home/pip/git/asmjs/subrepos/gcc/host-x86_64-pc-linux-gnu/gcc/' '-v' '-S' '-D'
'PERL_CORE' '-fwrapv' '-std=c90' '-O3' '-fno-strict-aliasing' '-w'
'-Wfatal-errors' '-o' 'tmp.s' '-mtune=generic' '-march=x86-64'




The call to sigsetjmp appears to be necessary to trigger the bug.

Sorry if this is a duplicate or a known issue; right now, I don't have
the time to investigate further. The call appears to be eliminated in a tree
optimization pass, so I'm tentatively choosing that component.