Subzero: Validate phi instructions after CFG construction.

Subzero: Validate phi instructions after CFG construction.

It checks that each phi label corresponds to an incoming edge, and that each incoming edge has a corresponding phi label.

It does not check that duplicate incoming edges get the same phi value.

Performance impact is minimal (~0.2%) despite the O(N^2) implementation.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4304
R=jpp@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=1aca23075ab7e2ddfd03c57782afa7c48c2d0354

[Jim Stichnoth, 2015-09-16 04:51:03]

stichnot@chromium.org changed reviewers:
+ ascull@google.com, jpp@chromium.org, kschimpf@google.com

[Jim Stichnoth, 2015-09-16 15:35:57]

Please hold off reviewing this.  I'm doing a proper implementation instead of
the O(N^2) algorithm.

[John, 2015-09-16 15:36:00]

lgtm

[Jim Stichnoth, 2015-09-16 18:25:27]

Committed patchset #2 (id:20001) manually as
1aca23075ab7e2ddfd03c57782afa7c48c2d0354 (presubmit successful).