[Webkit-unassigned] [Bug 151315] If B3->Air lowering moves a child to the result tmp when using an Inst with a x86-style UseDef operand, then other uses of that child should also use the result tmp

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Mon Nov 16 12:21:05 PST 2015


--- Comment #3 from Filip Pizlo <fpizlo at apple.com> ---
Whoa, our register allocator already does the magically correct thing.  This is Ben's comment:

            // We do not want the Use() of this move to interfere with the Def(), even if it is live
            // after the Move. If we were to add the interference edge, it would be impossible to
            // coalesce the Move even if the two Tmp never interfere anywhere.

This is the verbiage in the IRC paper:

    Move instructions are given special consideration. It is important not to create
    artifical interferences between the source and destination of a move. Consider the
        t := s
        x := ... s ... ...
        y := ... t ...
        ; copy
        ; use of s
        ; use of t
    After the copy instruction both s and t are live, and an interference edge would be
    added between s and t, since t is being defined at a point where s is live. The
    solution is to temporarily remove s from the live set and continue.

You are receiving this mail because:
You are the assignee for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.webkit.org/pipermail/webkit-unassigned/attachments/20151116/a0db5728/attachment.html>

More information about the webkit-unassigned mailing list