[Webkit-unassigned] [Bug 146846] New: jsc-tailcall: JavaScript functions should restore the stack pointer after a call

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=146846

            Bug ID: 146846
           Summary: jsc-tailcall: JavaScript functions should restore the
                    stack pointer after a call
    Classification: Unclassified
           Product: WebKit
           Version: 528+ (Nightly build)
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: basile_clement at apple.com
                CC: fpizlo at apple.com, ggaren at apple.com,
                    mark.lam at apple.com, msaboff at apple.com
            Blocks: 146477

The LLint and baseline JIT are already doing this, we statically know the stack size in the DFG, and we can get it from the LLVM stackmap in FTL code - so this should be an easy change.

Once https://bugs.webkit.org/show_bug.cgi?id=146845 is taken care of as well, this will allow us to:

 1) Get rid of the arity fixup return thunk (since the caller now knows where the stack pointer should be as an offset of its base pointer)

 2) Actually implement tail calls since they can shrink or extend the stack in unpredictable ways.

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