let phi = build_phi incoming "iftmp" builder in
The first two lines here are now familiar: the first adds the "merge"
-block to the Function object. The second block changes the insertion
+block to the Function object. The second changes the insertion
point so that newly created code will go into the "merge" block. Once
that is done, we need to create the PHI node and set up the block/value
pairs for the PHI.