2. Code duplication (addressing mode) during isel.
3. Other ideas from "Register-Sensitive Selection, Duplication, and
Sequencing of Instructions".
+4. Scheduling for reduced register pressure. E.g. "Minimum Register
+ Instruction Sequence Problem: Revisiting Optimal Code Generation for DAGs"
+ and other related papers.
+ http://citeseer.ist.psu.edu/govindarajan01minimum.html
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