+{- Note [Better Alt Heap Checks]
+If two function calls can share a return point, then they will also
+get the same info table. Therefore, it's worth our effort to make
+those opportunities appear as frequently as possible.
+
+Here are a few examples of how it should work:
+
+ STG:
+ case f x of
+ True -> <True code -- including allocation>
+ False -> <False code>
+ Cmm:
+ r = call f(x) returns to L;
+ L:
+ if r & 7 >= 2 goto L1 else goto L2;
+ L1:
+ if Hp > HpLim then
+ r = gc(r);
+ goto L;
+ <True code -- including allocation>
+ L2:
+ <False code>
+Note that the code following both the call to f(x) and the code to gc(r)
+should be the same, which will allow the common blockifier to discover
+that they are the same. Therefore, both function calls will return to the same
+block, and they will use the same info table.
+
+Here's an example of the Cmm code we want from a primOp.
+The primOp doesn't produce an info table for us to reuse, but that's okay:
+we should still generate the same code:
+ STG:
+ case f x of
+ 0 -> <0-case code -- including allocation>
+ _ -> <default-case code>
+ Cmm:
+ r = a +# b;
+ L:
+ if r == 0 then goto L1 else goto L2;
+ L1:
+ if Hp > HpLim then
+ r = gc(r);
+ goto L;
+ <0-case code -- including allocation>
+ L2:
+ <default-case code>
+-}
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