[Bug sanitizer/88234] New: UBsan and runtime error: signed integer overflow using unsigned vector

[noloader at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88234

            Bug ID: 88234
           Summary: UBsan and runtime error: signed integer overflow using
                    unsigned vector
           Product: gcc
           Version: 8.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: noloader at gmail dot com
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxin at gcc dot gnu.org
  Target Milestone: ---

I'm working on GCC135 from the compile farm. I'm experiencing a UBsan runtime
error for signed overflow when using unsigned vectors. The algorithms in the
real program depend on unsigned wrap; and not signed overflow.

gcc135:~$ cat test.cxx
#include <stdio.h>
#include <altivec.h>
#undef vector
#undef pixel
#undef bool

typedef unsigned char byte;
typedef __vector unsigned char uint8x16_p;
typedef __vector unsigned int  uint32x4_p;

int main(int argc, char* argv[])
{
  uint32x4_p a = { 1795745381, 0, 0, 0 };
  uint32x4_p b = { 1359893119, 0, 0, 0 };
  uint32x4_p c = vec_add(a, b);

  byte x[16];
  vec_vsx_st((uint8x16_p)c, 0, x);

  for (size_t i=0; i<16; ++i)
    printf("%02x ", x[i]);
  printf("\n");

  return 0;
}

The data "1795745381" and "1359893119" were taken from the first finding at
https://github.com/weidai11/cryptopp/issues/749.

And:

$ /opt/at12.0/bin/c++ -O1 -fsanitize=undefined -std=c++14 test.cxx -o test.exe
gcc135:~$ ./test.exe
test.cxx:15:25: runtime error: signed integer overflow: 1795745381 + 1359893119
cannot be represented in type 'int'
e4 38 17 bc 00 00 00 00 00 00 00 00 00 00 00 00

Finally:

gcc135:~$ /opt/at12.0/bin/c++ --version
c++ (GCC) 8.2.1 20180813 (Advance-Toolchain-at12.0) [revision 263510]
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.