[JSC] AI should check the given constant's array type when folding GetByVal into constant

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Yusuke Suzuki]

GetByVal has Double ArrayModes. So it expects to get Double arrays, and it will genetate a double value.
To ensure that, we have CheckStructure / CheckArray before this GetByVal.
But in AI phase, CheckStructure and CheckArray would not perform anything on a proven abstract value.
In that case, our GetByVal in AI gets unexpected array. If we do not perform any checks before using that to fold GetByVal into a constant, we have a bad time.


1: JSConstant(Array with CopyOnWrite | Contiguous) => like, ["bad"]
2: CheckStructure(@1, Array CopyOnWrite | Double) => It finally becomes OSR exit, but now, AI is not sure about it.
3: GetButterfly(@1)
4: GetByVal(@1, 0, @3, Array CopyOnWrite | Double) => If @4 can retrieve "bad" from @1, we attempt to convert @4 into "bad", but it is not acceptable since GetByVal(Double shape) should return a Double result.

We should perform array check on @1 constant before performing constant folding in AI.

[Yusuke Suzuki]

<rdar://problem/46092389>

[Yusuke Suzuki]

Created attachment 359098 [details]
Patch

[Yusuke Suzuki]

Created attachment 359099 [details]
Patch

[Keith Miller]

Comment on attachment 359099 [details]
Patch

r=me.

[Yusuke Suzuki]

Committed r239964: <https://trac.webkit.org/changeset/239964>