Compute ipa-predicates for conditionals involving __builtin_expect_p

Compute ipa-predicates for conditionals involving __builtin_expect_p

std::vector allocator looks as follows:

__attribute__((nodiscard))
struct pair * std::__new_allocator<std::pair<unsigned int, unsigned int> >::allocate (struct __new_allocator * const this, size_type __n, const void * D.27753)
{
  bool _1;
  long int _2;
  long int _3;
  long unsigned int _5;
  struct pair * _9;

  <bb 2> [local count: 1073741824]:
  _1 = __n_7(D) > 1152921504606846975;
  _2 = (long int) _1;
  _3 = __builtin_expect (_2, 0);
  if (_3 != 0)
    goto <bb 3>; [10.00%]
  else
    goto <bb 6>; [90.00%]

  <bb 3> [local count: 107374184]:
  if (__n_7(D) > 2305843009213693951)
    goto <bb 4>; [50.00%]
  else
    goto <bb 5>; [50.00%]

  <bb 4> [local count: 53687092]:
  std::__throw_bad_array_new_length ();

  <bb 5> [local count: 53687092]:
  std::__throw_bad_alloc ();

  <bb 6> [local count: 966367641]:
  _5 = __n_7(D) * 8;
  _9 = operator new (_5);
  return _9;
}

So there is check for allocated block size being greater than max_size which is
wrapper in __builtin_expect.  This makes ipa-fnsummary to give up analyzing
predicates and it will miss the fact that the two different calls to __throw
will be optimized out if __n is larady smaller than 1152921504606846975 which
it is after _M_check_len.

This patch extends ipa-fnsummary to understand functions that return their
parameter.

gcc/ChangeLog:

	PR tree-optimization/109849
	* ipa-fnsummary.cc (decompose_param_expr): Skip
	functions returning its parameter.
	(set_cond_stmt_execution_predicate): Return early
	if predicate was constructed.

gcc/testsuite/ChangeLog:

	PR tree-optimization/109849
	* gcc.dg/ipa/pr109849.c: New test.