commit db0c86fa5f03794838ee6d1d301ca34d41f20fca
author clemensh <clemensh@chromium.org> Thu Dec 01 08:52:31 2016
committer Commit bot <commit-bot@chromium.org> Thu Dec 01 08:53:04 2016
tree 9947f1f18bbb20587e8e7a30dd728d0485c5bada
parent c71fc9902d5f6b2cf6beedde52e44a391b856c19

[base] Define CHECK comparison for signed vs. unsigned

The current CHECK/DCHECK implementation fails statically if a signed
value is compared against an unsigned value. The common solution is to
cast on each caller, which is tedious and error-prone (might hide bugs).
This CL implements signed vs. unsigned comparisons by executing up to
two comparisons. For example, if i is int32_t and u is uint_32_t, a
DCHECK_LE(i, u) would create the check
i <= 0 || static_cast<uint32_t>(i) <= u.
For checks against constants, at least one of the checks can be removed
by compiler optimizations.

The tradeoff we have to make is to sometimes silently execute an
additional comparison. And we increase code complexity of course, even
though the usage is just as easy (or even easier) as before.

The compile time impact seems to be minimal:
I ran 3 full compilations for Optdebug on my local machine, one time on
the current ToT, one time with this CL plus http://crrev.com/2524093002.
Before: 143.72 +- 1.21 seconds
Now: 144.18 +- 0.67 seconds

In order to check that the new comparisons are working, I refactored
some DCHECKs in wasm to use the new magic, and added unit test cases.

R=ishell@chromium.org, titzer@chromium.org
CC=ahaas@chromium.org, bmeurer@chromium.org

Committed: https://crrev.com/5925074a9dab5a8577766545b91b62f2c531d3dc
Review-Url: https://codereview.chromium.org/2526783002
Cr-Original-Commit-Position: refs/heads/master@{#41275}
Cr-Commit-Position: refs/heads/master@{#41411}