| Summary: | [JSC] branchTest8 should not emit tst for Zero/NonZero cases | ||||||||
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| Product: | WebKit | Reporter: | Yusuke Suzuki <ysuzuki> | ||||||
| Component: | New Bugs | Assignee: | Yusuke Suzuki <ysuzuki> | ||||||
| Status: | RESOLVED FIXED | ||||||||
| Severity: | Normal | CC: | ews-watchlist, keith_miller, mark.lam, msaboff, saam, tzagallo, webkit-bug-importer | ||||||
| Priority: | P2 | Keywords: | InRadar | ||||||
| Version: | WebKit Nightly Build | ||||||||
| Hardware: | Unspecified | ||||||||
| OS: | Unspecified | ||||||||
| Attachments: |
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Description
Yusuke Suzuki
2021-07-30 20:11:42 PDT
Created attachment 434685 [details]
Patch
Created attachment 434686 [details]
Patch
Comment on attachment 434686 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=434686&action=review r=me > Source/JavaScriptCore/ChangeLog:9 > + unnecessary. This is because the mask is truncated into 8bit, which /unnecessary/unnecessarily/. > Source/JavaScriptCore/ChangeLog:14 > + This patch removes this unnecessary truncation since Zero/NonZero does > + not care high bits of mask in branchTest8. I think it's worth pointing out that this is ok because the ResultCondition version of mask8OnCondition() is always used to generate a mask that is only used against a value that is loaded with MacroAssemblerHelpers::load8OnCondition(). For Zero/NonZero conditions, load8OnCondition() will always zero fill the upper bytes. The 0 filled upper bytes will not affect the result of a branch on zero or branch on not zero. Comment on attachment 434686 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=434686&action=review >> Source/JavaScriptCore/ChangeLog:9 >> + unnecessary. This is because the mask is truncated into 8bit, which > > /unnecessary/unnecessarily/. Fixed. >> Source/JavaScriptCore/ChangeLog:14 >> + not care high bits of mask in branchTest8. > > I think it's worth pointing out that this is ok because the ResultCondition version of mask8OnCondition() is always used to generate a mask that is only used against a value that is loaded with MacroAssemblerHelpers::load8OnCondition(). For Zero/NonZero conditions, load8OnCondition() will always zero fill the upper bytes. The 0 filled upper bytes will not affect the result of a branch on zero or branch on not zero. Sounds good. Added. Committed r280508 (240140@main): <https://commits.webkit.org/240140@main> |