[webkit-reviews] review denied: [Bug 227201] Add a new pattern to instruction selector to use BFI supported by ARM64 : [Attachment 432140] Patch
bugzilla-daemon at webkit.org
bugzilla-daemon at webkit.org
Thu Jun 24 09:22:17 PDT 2021
Filip Pizlo <fpizlo at apple.com> has denied Yijia Huang <yijia_huang at apple.com>'s
request for review:
Bug 227201: Add a new pattern to instruction selector to use BFI supported by
ARM64
https://bugs.webkit.org/show_bug.cgi?id=227201
Attachment 432140: Patch
https://bugs.webkit.org/attachment.cgi?id=432140&action=review
--- Comment #2 from Filip Pizlo <fpizlo at apple.com> ---
Comment on attachment 432140
--> https://bugs.webkit.org/attachment.cgi?id=432140
Patch
View in context: https://bugs.webkit.org/attachment.cgi?id=432140&action=review
> Source/JavaScriptCore/ChangeLog:28
> + Pattern 2:
> + mask1 = (1 << width) - 1
> + mask2 = ~(mask1 << lsb)
> + d = ((n & mask1) << lsb) | (d & mask2)
> +
> + Pattern 3:
> + mask1 = (1 << width) - 1
> + d = ((n & mask1) << lsb) | d
Is this right?
Say that d = 0x42424242
Say that mask1 = 0xFF
Say that mask2 = 0xFF00FFFF
Say that lsb = 16
Say that n = 0xBC
Note that 0x42 | 0xBC = 0xFE
With pattern 2, we will get:
((0xBC & 0xFF) << 16) | (0x42424242 & 0xFF00FFFF)
= 0xBC0000 | 0x42004242
= 0x42BC4242
With pattern 3, we will get:
((0xBC & 0xFF) << 16) | 0x42424242
= 0xBC0000 | 0x42424242
= 0x42FE4242
I don't think they're equivalent patterns.
More information about the webkit-reviews
mailing list