M7: SelectionDAG

[tamnd]

Six weeks. Part VI, SelectionDAG. Nine lessons and the first three codegen blueprints.

Exit criterion. irx.dag parses -debug-only=isel output for three targets without target specific code.

Tasks

• S01 to S09
• BP-CG-DAG, BP-CG-LEGAL, BP-CG-ISEL
• irx.dag
• The DAGViewer widget at full capability
• The legalization animation

Gates

• irx.dag handles three targets with no target specific parsing
• S09 measurably helps, tested by giving readers an unfamiliar DAG dump before and after and comparing comprehension answers

S09 gets measured rather than assumed because its entire value is a claim about legibility. Every other lesson can be checked by asking whether a reader can do the thing. This one claims that after reading it, a wall of output stops being a wall, and that is only worth believing if somebody tested it.