We can actually eliminate certain effectful operations like loads and
speculative number operations during representation selection if we
discover that their value outputs are unused (we also propagate this
information through pure operations as well, so that we remove the
maximum number of effectful nodes possible).

R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2168023002
Cr-Commit-Position: refs/heads/master@{#37928}