[Webkit-unassigned] [Bug 138315] [JSC] Erratum (835769) in Cortex-A53

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=138315

Akos Kiss <akiss at inf.u-szeged.hu> changed:

           What    |Removed                     |Added
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 Attachment #240860|                            |review?, commit-queue?
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--- Comment #2 from Akos Kiss <akiss at inf.u-szeged.hu> ---
Created attachment 240860
  --> https://bugs.webkit.org/attachment.cgi?id=240860&action=review
Proposed patch.

Built with Tools/Scripts/build-jsc --gtk --cmakeargs="-DWTF_CPU_ARM64_CORTEXA53=ON", no regression.

Some extra comments:

1) The ARM64 assembler runs into the nop generating code path in 162 jsc tests. E.g., in sunspider-1.0/string-fasta.js.default it generates something like this below:

      57:< 1:-4>        GetLocal(@1, JS, Int32, arg1(B<Int32>/FlushedInt32), machine:arg1, R:Variables(7), bc#98) predicting Int32
            0x7fa947f30c:    ldur   w0, [fp, #56]
      58:< 2:-4>        ArithMul(Int32:@45, Int32:@57, Number, Int32, CheckOverflowAndNegativeZero, bc#98)
            0x7fa947f310:    nop   
            0x7fa947f314:    smaddl x1, w2, w0, x31


2) For now, offlineasm generates no extra nops, since the LLInt asm sources contain no patterns which would trigger the nop-inserting code. The offlineasm part of the patch has been tested with crafted code (of no real use), however, and the generated assembly was OK. E.g.:

    "\tldr x2, [x13, #16]\n"                                 // /home/akiss/devel/WebKit/Source/JavaScriptCore/llint/LowLevelInterpreter.asm:1375
#if CPU(ARM64_CORTEXA53)
    "\tnop\n"                                                // /home/akiss/devel/WebKit/Source/JavaScriptCore/llint/LowLevelInterpreter.asm:1376
#endif
    "\tmadd w1, w1, w1, wzr\n"                               // /home/akiss/devel/WebKit/Source/JavaScriptCore/llint/LowLevelInterpreter.asm:1376

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