[Bug middle-end/71762] New: [4.9 Regression] ifcombine wrong codegen with uninitialized data

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71762

            Bug ID: 71762
           Summary: [4.9 Regression] ifcombine wrong codegen with
                    uninitialized data
           Product: gcc
           Version: 4.9.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ibuclaw at gdcproject dot org
  Target Milestone: ---

In the following minimal test built with: g++ -O2
---
#include <stdio.h>

struct S
{
  void* get()
  {
    return NULL;
  }

  ~S()
  {
    printf("dtor\n");
  }
};


void foo(void* x)
{
  printf("foo\n");
}


void testFunc(int len)
{
  bool __cond59;
  bool __cond60;

  foo ((__cond60 = len > 1, __cond60) ? NULL : (__cond59 = len == 1, __cond59)
? S().get() : NULL);

  if (!__cond60)
    {
      if (__cond59)
        {
          printf("fail\n");
        }
    }
}

void check(void (*dg)(int))
{
  dg(2);
}

int main()
{
  check(&testFunc);
}
---

The optimizer simplifies the two if statements as: `if (__cond59 > __cond60)`,
where __cond59 is never initialized in `testFunc`.

This regression is only present in 4.9.  gcc-4.8 and gcc-5 are unaffected.

The commit that caused the regression was r204194, and it went away after
r217496.