With Int32Add we lose the int/uint distinction, so later, in simplified lowering we can make a wrong decision. E.g., see the attached test case, where we lower NumberAdd -> Int32Add because inputs are Uint32, but during simplified lowering we change the inputs to Int32, so we get a wrong result.
Simplified lowering will lower the NumberAdd operations anyway, so we should lose performance.
BUG=
R=bmeurer@chromium.org
Review URL: https://codereview.chromium.org/721723004
Cr-Commit-Position: refs/heads/master@{#25368}
