[Webkit-unassigned] [Bug 201631] New: [JSC] Manually adding 256 size class to make the current JSC allocation behavior stable

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=201631

            Bug ID: 201631
           Summary: [JSC] Manually adding 256 size class to make the
                    current JSC allocation behavior stable
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: ysuzuki at apple.com

We have old and hacky code like this.

add(sizeof(UnlinkedFunctionCodeBlock));

This manually adds sizeof(UnlinkedFunctionCodeBlock) to size class sequence.
This is really fragile since size-class sequence depends on UnlinkedFunctionCodeBlock size.
The size-class sequence is very fundamental thing for JSC's allocation pattern. And changing this completely changes how JSC allocates.

bug 201613 changed sizeof(UnlinkedFunctionCodeBlock) and dramatically changes the allocation behavior of JSC.
We should make the previous allocation pattern stable.

Instead of adding `add(sizeof(UnlinkedFunctionCodeBlock));`, adding `add(256)` directly to make the previous behavior as baseline.

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