Run a simplification pass before code generation.

The code generators assume things that only the instruction
simplier ensures. So it has to be run last in case previous
optimiziations broke those assumptions.

bug:21865464

(cherry picked from commit b2bdfce7f805b00668a2521b1c939a0aafb2be49)

Change-Id: Ibf4384a911e400eb7586bbf6b4edd6351034cbd8
4 files changed