[Bug rtl-optimization/43721] Failure to optimise (a/b) and (a%b) into single __aeabi_idivmod call

["mans at mansr dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from mans at mansr dot com  2010-04-14 21:34 -------
The C99 standard says this about division by zero:

  The result of the / operator is the quotient from the division
  of the first operand by the second; the result of the % operator
  is the remainder. In both operations, if the value of the second
  operand is zero, the behavior is undefined.

The ARM ABI states the following about the __aeabi_div0() function:

  The *div0 functions:
  - Return the value passed to them as a parameter.
  - Or, return a fixed value defined by the execution environment (such as 0).
  - Or, raise a signal (often SIGFPE) or throw an exception, and do not return.
  [...]
  The *div and *divmod functions may be inlined by a tool chain. It is
  Q-o-I whether an inlined version calls *div0 out of line or returns the
  values that would have been returned by a particular value-returning
  version of *div0.

I interpret these as saying the application may make no assumptions about
the behaviour after a division (or modulus) by zero.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43721