[Bug middle-end/82286] Wrong array subscript is above array bounds

[hermantenbrugge at home dot nl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82286

--- Comment #4 from Herman ten Brugge <hermantenbrugge at home dot nl> ---
Created attachment 42238
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42238&action=edit
modified test case

I modified the testcase a little bit and did some debugging.

The code outputs a failure if compiled with:
gcc -O3 -Wall -c tst.c -DERROR -fdump-tree-cunrolli-details
tst.c: In function 'mtrx_decompose_matrix':
tst.c:34:17: warning: array subscript is above array bounds [-Warray-bounds]
  sum += tmp.data[row][sub];

The code is ok of compiled with:
gcc -O3 -Wall -c tst.c -DERROR -fdump-tree-cunrolli-details
-fno-aggressive-loop-optimizations
or:
gcc -O3 -Wall -c tst.c -fdump-tree-cunrolli-details

The dumpfile that are created are in case of error containing or if
-fno-aggressive-loop-optimizations is given:
...
Analyzing # of iterations of loop 3
  exit condition [0, + , 1](no_overflow) < row_8
  bounds on difference of bases: 0 ... 4294967294
  result:
    # of iterations row_8, bounded by 4294967294
...

The dumpfile looks correct in the case the sqrtf function is not used:
...
Analyzing # of iterations of loop 3
  exit condition [0, + , 1](no_overflow) < row_5
  bounds on difference of bases: 0 ... 5
  result:
    # of iterations row_5, bounded by 5
...

Something must go wrong when aggressive-loop-optimizations is enabled.