[Bug tree-optimization/71288] New: [7 Regression] Time and memory hog during if-conversion at -O3

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71288

            Bug ID: 71288
           Summary: [7 Regression] Time and memory hog during
                    if-conversion at -O3
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Keywords: compile-time-hog, memory-hog
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---

gcc-7.0.0-alpha20160522 consumes lots of memory and time (indefinite time?)
when compiling the following testcase at -O3:

unsigned short int hb;
short int kr;

void
o8 (void)
{
  unsigned short int ov;

  while (hb < 1)
  {
    if (hb != kr)
      hb = 0;
    for (ov = 0; ov < 16; ++ov)
    {
      kr = 0;
      hb -= ((hb != 0) ? (ov < hb) : 1);
    }
  }
}

% timeout 15 x86_64-pc-linux-gnu-gcc-7.0.0-alpha20160522 -c -O3 -w gjpx2kcj.c
% echo $?
124

Strictly speaking, the testcase is not fully reduced. It is the minimal version
which still demonstrates the same hottest path in perf top as the original
program:

  26.77%  cc1           [.] (anonymous namespace)::pass_if_conversion::execute