[Webkit-unassigned] [Bug 71373] Enable the DFG JIT on x86-64 Linux platforms

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=71373





--- Comment #28 from Filip Pizlo <fpizlo at apple.com>  2011-11-09 12:31:33 PST ---
(In reply to comment #18)
> (From update of attachment 114235 [details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=114235&action=review
> 
> > Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp:-734
> > -        MacroAssembler::Jump tooBig = m_jit.branch32(MacroAssembler::GreaterThan, scratchReg, TrustedImm32(0xff));
> 
> I think this call is unnecessary.
> 1) The previous check <=, so the it is always >
> 2) The following code would be dead code.
> I think that it is working on x86 is a pure luck, since "jmp 0" jumps to the next instruction after the "jmp".

No.  The first check is BelowOrEqual, which is an unsigned comparison.  The second check is GreaterThan, which is a signed comparison.

The tooBig branch should be linked to this line:

        m_jit.move(TrustedImm32(255), scratchReg);

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