error.xml

<article
	 xmlns:omg="http://www.omegahat.org"
	 xmlns:r="http://www.r-project.org"
	 xmlns:c="http://www.C.org">

<section>
<title></title>


<para>
The idea here is to find calls to PROBLEM-ERROR or Rf_error in C code. 
</para>


<para>
  We start with error.c, a very simple routine that checks the lengths of its two inputs
  and raises an error if the lengths are not the same.
  We generate the ir from this C code.
<sh:code>
make error.ir    
</sh:code>
</para>


<para>
<r:code>
library(Rllvm)
m = parseIR("error.ir")
f = m$r_routine
</r:code>

Now let's find any calls to Rf_error.
<r:code>
b = getBlocks(f)
</r:code>
For each block, we iterate over the instructions, looking for calls to Rf_error.
For a single block, we do this with
<r:code>
nm = sapply(b[[2]], function(x) {
                 if(!is(x, "CallInst"))
                    return("")

		 getName(getCalledFunction(x))
		 })
w = nm %in% c("Rf_error", "Rf_warning")		 
</r:code>

</para>
<para>
  See findErrorWarningCalls in findCErrorCall.R.
<r:code>
v = findErrorWarningCalls(m$r_routine)
</r:code>
This returns a list for each Block in the routine.
Two of these are empty.
We can recover the enclosing Block from any call returned using
<r:func>getParent</r:func>.
</para>

<para>
  Now that we have a call to Rf_error, we have achieved our initial goal.
  If we wanted to determine the nature of the error condition, we could attempt
  to reconstruct the high-level C code. For this, we might be better working from the AST
  rather than the IR.
  From the IR, we can find the incoming block for this block.
</para>


</section>
</article>