Re: strange failure in plpgsql_control tests (on fulmar, ICC 14.0.3)

I wrote:
> Ouch. That test is in fact new as of 31 Dec, and what this seems to
> prove is that plpgsql's handling of loop-variable overflow doesn't
> work on fulmar.

Some of the other icc-using critters haven't reported in since
December, either :-(

Looking at the code, we do this like so:

/*
* Increase/decrease loop value, unless it would overflow, in which
* case exit the loop.
*/
if (stmt->reverse)
{
if ((int32) (loop_value - step_value) > loop_value)
break;
loop_value -= step_value;
}
else
{
if ((int32) (loop_value + step_value) < loop_value)
break;
loop_value += step_value;
}

I imagine what's happening is that the compiler is assuming no overflow
occurs (due to lacking any equivalent of -fwrapv), then deducing that the
if-tests are no-ops and throwing them away.

We could avoid the dependency on -fwrapv with something like

if (stmt->reverse)
{
if (loop_value < (PG_INT32_MIN + step_value))
break;
loop_value -= step_value;
}
else
{
if (loop_value > (PG_INT32_MAX - step_value))
break;
loop_value += step_value;
}

which is safe because we enforce step_value > 0. It's kind of ugly
because it hard-codes knowledge of what the limits are, but we may not
have much choice.

regards, tom lane