[Webkit-unassigned] [Bug 114495] New: LLInt should not use d8 register as scratch register

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=114495

           Summary: LLInt should not use d8 register as scratch register
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: sg5.lee at samsung.com


Currently, LLInt uses d8 register as scratch register as followings:

ARM_SCRATCH_FPR = SpecialRegister.new("d8")    in arm.rb
C_LOOP_SCRATCH_FPR = SpecialRegister.new("d8") in cloop.rb

However, AAPCS §5.1.2.1 says

Registers s16-s31 (d8-d15, q4-q7) must be preserved across subroutine calls; registers s0-s15 (d0-d7, q0-q3) do not need to be preserved (and can be used for passing arguments or returning results in standard procedure-call variants). Registers d16-d31 (q8-q15), if present, do not need to be preserved.

Therefore it should not use d8 for that purpose.

I think it would be safe to use d6.
(Register d7 is already in use for other purpose. )

ARM_SCRATCH_FPR = SpecialRegister.new("d6")    in arm.rb
C_LOOP_SCRATCH_FPR = SpecialRegister.new("d6") in cloop.rb

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