[turbofan] ReceiverOrNullOrUndefined feedback for JSEqual.
This changes the ReceiverOrOddball feedback on JSStrictEqual to ReceiverOrNullOrUndefined feedback, which can also safely be consumed by JSEqual (we cannot generally accept any oddball here since booleans trigger implicit conversions, unfortunately). Thus we replace the previously introduced CheckReceiverOrOddball with CheckReceiverOrNullOrUndefined, and drop CheckOddball, since we will no longer collect Oddball feedback separately. TurboFan will then turn a JSEqual[ReceiverOrNullOrUndefined] into a sequence like this: ``` left = CheckReceiverOrNullOrUndefined(left); right = CheckReceiverOrNullOrUndefined(right); result = if ObjectIsUndetectable(left) then ObjectIsUndetectable(right) else ReferenceEqual(left, right); ``` This significantly improves the peak performance of abstract equality with Receiver, Null or Undefined inputs. On the test case outlined in http://crbug.com/v8/8356 we go from naive: 2946 ms. tenary: 2134 ms. to naive: 2230 ms. tenary: 2250 ms. which corresponds to a 25% improvement on the abstract equality case. For regular code this will probably yield more performance, since we get rid of the JSEqual operator, which might have arbitrary side effects and thus blocks all kinds of TurboFan optimizations. The JSStrictEqual case is slightly slower now, since it has to rule out booleans as well (even though that's not strictly necessary, but consistency is key here). This way developers can safely use `a == b` instead of doing a dance like `a == null ? b == null : a === b` (which is what dart2js does right now) when both `a` and `b` are known to be Receiver, Null or Undefined. The abstract equality is not only faster to parse than the tenary, but also generates a shorter bytecode sequence. In the test case referenced in http://crbug.com/v8/8356 the bytecode for `naive` is ``` StackCheck Ldar a1 TestEqual a0, [0] JumpIfFalse [5] LdaSmi [1] Return LdaSmi [2] Return ``` which is 14 bytes, whereas the `tenary` function generates ``` StackCheck Ldar a0 TestUndetectable JumpIfFalse [7] Ldar a1 TestUndetectable Jump [7] Ldar a1 TestEqualStrict a0, [0] JumpIfToBooleanFalse [5] LdaSmi [1] Return LdaSmi [2] Return ``` which is 24 bytes. So the `naive` version is 40% smaller and requires fewer bytecode dispatches. Bug: chromium:898455, v8:8356 Change-Id: If3961b2518b4438700706b3bd6071d546305e233 Reviewed-on: https://chromium-review.googlesource.com/c/1297315Reviewed-by: Jaroslav Sevcik <jarin@chromium.org> Commit-Queue: Benedikt Meurer <bmeurer@chromium.org> Cr-Commit-Position: refs/heads/master@{#56948}
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