[Bug tree-optimization/100086] New: spurious -Wnonnull with __builtin_expect

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100086

            Bug ID: 100086
           Summary: spurious -Wnonnull with __builtin_expect
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The following has been reduced from Red Hat bug
https://bugzilla.redhat.com/show_bug.cgi?id=1948775.  In the original code the
warning points to the this pointer in a call to a member function (which first
became subject to the warning in GCC 11) but the same issue can be reproduced
with any other nonnull function such as the call to __builtin_puts(0B) in the
IL.  Replacing the __builtin_expect call with a plain test avoids the warning,
as does removing the indirection via AssertionResult.

$ cat rhbz1948775.C && gcc -O2 -S -Wall -fdump-tree-post_ipa_warn=/dev/stdout
rhbz1948775.C
struct string {
  char *p;
};

string GetMessage();

struct AssertionResult
{
  AssertionResult (bool b) : b_(b) { }
  operator bool() const {
    return b_;
  }
  bool b_;
};

struct AssertHelper {
  AssertHelper (const char*);
  void operator=(int);
};

struct RefPtr
{
  ~RefPtr()
  {
    if (__builtin_expect ((p != 0), 1))
      __builtin_puts (p);
  }

  operator bool() const {
    return !!p;
  }

  char *p;
};

RefPtr take ();

void TestBody ()
{
  RefPtr emptyTake = take ();
  if (!AssertionResult (!emptyTake))
    return AssertHelper(GetMessage().p) = 1;
}

;; Function TestBody (_Z8TestBodyv, funcdef_no=8, decl_uid=2417, cgraph_uid=9,
symbol_order=8)

In destructor ‘RefPtr::~RefPtr()’,
    inlined from ‘void TestBody()’ at rhbz1948775.C:43:1:
rhbz1948775.C:26:22: warning: argument 1 null where non-null expected
[-Wnonnull]
   26 |       __builtin_puts (p);
      |       ~~~~~~~~~~~~~~~^~~
rhbz1948775.C: In function ‘void TestBody()’:
rhbz1948775.C:26:22: note: in a call to built-in function ‘int
__builtin_puts(const char*)’
void TestBody ()
{
  struct RefPtr emptyTake;
  struct string D.2464;
  struct AssertHelper D.2492;
  bool _1;
  char * _2;
  char * _14;
  bool _15;
  char * _16;
  bool _17;
  long int _18;
  long int _19;
  long int _20;
  long int _21;
  char * _22;
  bool _23;
  long int _24;
  long int _25;

  <bb 2> [local count: 1073741824]:
  emptyTake = take (); [return slot optimization]
  _14 = emptyTake.p;
  _15 = _14 != 0B;
  _1 = _14 == 0B;
  if (_1 != 0)
    goto <bb 9>; [79.76%]
  else
    goto <bb 3>; [20.24%]

  <bb 3> [local count: 217325344]:
  D.2464 = GetMessage ();

  <bb 4> [local count: 217325344]:
  _2 = D.2464.p;
  AssertHelper::AssertHelper (&D.2492, _2);

  <bb 5> [local count: 217325344]:
  AssertHelper::operator= (&D.2492, 1);

  <bb 6> [local count: 217325344]:
  D.2492 ={v} {CLOBBER};
  _16 = emptyTake.p;
  _17 = _16 != 0B;
  _18 = (long int) _17;
  _19 = _18;
  if (_19 != 0)
    goto <bb 7>; [90.00%]
  else
    goto <bb 8>; [10.00%]

  <bb 7> [local count: 195592809]:
  __builtin_puts (_16);

  <bb 8> [local count: 217325344]:
  emptyTake ={v} {CLOBBER};
  emptyTake ={v} {CLOBBER};
  goto <bb 12>; [100.00%]

  <bb 9> [local count: 856416481]:
  _20 = (long int) _15;
  _21 = _20;
  if (_21 != 0)
    goto <bb 10>; [90.00%]
  else
    goto <bb 11>; [10.00%]

  <bb 10> [local count: 770774832]:
  __builtin_puts (0B);                <<< -Wnonnull

  <bb 11> [local count: 856416481]:
  emptyTake ={v} {CLOBBER};
  emptyTake ={v} {CLOBBER};

  <bb 12> [local count: 1073741824]:
  return;

  <bb 13> [count: 0]:
<L8>:
  D.2492 ={v} {CLOBBER};
  _22 = emptyTake.p;
  _23 = _22 != 0B;
  _24 = (long int) _23;
  _25 = _24;
  if (_25 != 0)
    goto <bb 14>; [0.00%]
  else
    goto <bb 15>; [0.00%]

  <bb 14> [count: 0]:
  __builtin_puts (_22);

  <bb 15> [count: 0]:
  emptyTake ={v} {CLOBBER};
  resx 2

}