[Bug tree-optimization/90837] New: Generate infinite loop when using -ftree-vrp

[zhongyunde at huawei dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90837

            Bug ID: 90837
           Summary: Generate infinite loop when using -ftree-vrp
           Product: gcc
           Version: 8.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhongyunde at huawei dot com
  Target Milestone: ---

Created attachment 46481
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46481&action=edit
a simplified test case

compile loop.c with follow command on x86 target , it will Generate infinite
loop, which is not expect.

  /home/gcc-serials/GCC/gcc-810/binary/bin/gcc -S -O2 -dpA loop.c
-fdump-tree-vrp-details 

test case attached.

    if (uwtotalUserNum > 5) {
        for (uwUserCountCell0 = 0; uwUserCountCell0 < (uwtotalUserNum - 1);
uwUserCountCell0++) {
            for (uwUserCountCell1 = 0; uwUserCountCell1 < (uwtotalUserNum -
(uwUserCountCell0 + 1)); uwUserCountCell1++) {
                if
(pstruCodeDetectBuf->auwMulRRUPeakUsrInfo[0][uwUserCountCell1].hfPeakValue <
pstruCodeDetectBuf->auwMulRRUPeakUsrInfo[0][uwUserCountCell1 + 1].hfPeakValue)
{

                   
pstruDetectUserInfoCell0[uwUserCountCell1].uwRachRelativeValue
                                            =
pstruDetectUserInfoCell0[uwUserCountCell1 + 1].uwRachRelativeValue;


                }
            }

        }


in vrp1 dump , there is similar code:

<bb 10> :
  # PHI

<bb 11> :
  # PHI
  ...
if (_10 < _12)
   goto <bb 12>
else
   goto <bb 10>

<bb 12> 
   ...
    goto <bb 10>