[Webkit-unassigned] [Bug 48060] Speed up op_jeq_null and op_jneq_null in JIT

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=48060





--- Comment #10 from Gabor Loki <loki at webkit.org>  2010-10-27 01:04:02 PST ---
>         enum { NullTag =         0xffffffff };
>         enum { UndefinedTag =    0xfffffffe };
> 
> Then we don't need any bit logic at all, and can replace it with
> addJump(branch32(GreaterOrEqual, regT1, Imm32(JSValue::UndefinedTag)), target);

I took a closer look into emit_op_jneq_null and emit_op_jeq_null and there is no check for non-double values. Both functions check MasqueradesAsUndefined bit and NullTag or UndefinedTag to determine the source is null (or not). So, this suggestion will not work. Although we can insert an unsigned comparison to the LowestTag to check for double, but this case will add new comparisons which will influence the execution speed in different ways for different control flow.

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