[Bug tree-optimization/59124] [4.9/5/6 Regression] Wrong warnings "array subscript is above array bounds"

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59124

baoshan <pangbw at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pangbw at gmail dot com

--- Comment #18 from baoshan <pangbw at gmail dot com> ---
I see this issue on 5.2.0 too:

cat test.c
unsigned baz[6];
void test(unsigned *bar, unsigned n) {
     unsigned i, j;
     if (n > 6) {
          n = 6;
     }
     for (i = 1; i < n; i++) {
          for (j = i - 1; j > 0; j--) {
               bar[j - 1] = baz[j - 1];
          }
     }
}
bpg@ala-bpg-lx1$./cross/bin/arm-linux-gnueabi-gcc -c -Wall -O3 test.c
test.c: In function ‘test’:
test.c:9:32: warning: array subscript is above array bounds [-Warray-bounds]
                bar[j - 1] = baz[j - 1];
                                ^
test.c:9:32: warning: array subscript is above array bounds [-Warray-bounds]
bpg@ala-bpg-lx1$./cross/bin/arm-linux-gnueabi-gcc -v
Using built-in specs.
COLLECT_GCC=./cross/bin/arm-linux-gnueabi-gcc
COLLECT_LTO_WRAPPER=/net/ala-rsu-lx1/ala-rsu-lx11/bpg/SHARE/GCC520/X_520/cross/libexec/gcc/arm-linux-gnueabi/5.2.0/lto-wrapper
Target: arm-linux-gnueabi
Configured with: ../gcc-5.2.0/configure
--prefix=/net/ala-rsu-lx1/ala-rsu-lx11/bpg/SHARE/GCC520/X_520/cross
--target=arm-linux-gnueabi --enable-languages=c,c++ --d\
isable-multilib
Thread model: posix
gcc version 5.2.0 (GCC)
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Subject: [Bug fortran/67531] FAIL: gfortran.dg/ieee/large_2.f90   -O0  execution test
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg531

--- Comment #1 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> ---
Thanks for the report. So apparently, on powerpc64le-unknown-linux-gnu, long
double division of 1.0L by 3.0L with rounding mode set to "down" is incorrect.

Can you compile and run the following C test case?

$ cat z.c
#include <fenv.h>
#include <stdio.h>

int main (void)
{
  long double x1, x2, x;

  fesetround (FE_UPWARD);
  x1 = 1;
  x = 3;
  x1 = x1 / x;

  fesetround (FE_DOWNWARD);
  x2 = 1;
  x = 3;
  x2 = x2 / x;

  printf ("%.40Lg\n", x1);
  printf ("%.40Lg\n", x2);
}
$ gcc z.c -lm && ./a.out
0.3333333333333333333423683514373792036167
0.3333333333333333333152632971252415927665


Above is the result on x86_64-linux, so the outcome shouldn't be identical, but
the two numbers output should not be equal.