Some Cava optimization

• Optimize Cava's CPU schedule.
• Add fork-fusion pass for fusing unrelated but adjacent fork-joins.
• Add intrinsic functions to math expressions.
• Add print pass for debugging schedules.
• Avoid some edges in dot output to help little xdot out.
• TODO: need more relaxed bounds for forkify to parallelize demosaic.

juno_samples/cava/src/cpu.sch

@@ -68,6 +68,7 @@ fixpoint {
 ccp(median);
 array-to-product(median);
 sroa(median);
+phi-elim(median);
 predication(median);
 simpl!(median);