RESOLVED FIXED 289114
[JSC] emitEncodeStructureID should be a no-op when the structureIDMask is -1 
https://bugs.webkit.org/show_bug.cgi?id=289114
Summary [JSC] emitEncodeStructureID should be a no-op when the structureIDMask is -1
David Degazio
Reported 2025-03-04 13:59:22 PST
Currently in AssemblyHelpers::emitEncodeStructureID, we generate a 64-bit AND to mask the structure ID to the significant bits. However, this mask is currently just 32-bit -1, which under the current macro assembler semantics ends up just getting sign-extended, meaning we do a 64-bit AND with a 64-bit -1 which is a no-op. This is fine, since the structure ID is a 32-bit quantity anyway, and we don't use the full 64-bit register after encoding anywhere in the codebase I can find - effectively, since we're using the lower 32-bit half of the register, we are getting the masking for free. But since that's the case, we should elide this AND since it's not doing anything useful.
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Radar WebKit Bug Importer
Comment 1 2025-03-04 13:59:30 PST
<rdar://problem/146142200>
David Degazio
Comment 2 2025-03-04 14:17:11 PST
Pull request: https://github.com/WebKit/WebKit/pull/41876
EWS
Comment 3 2025-03-06 10:39:47 PST
Committed 291713@main (b6667ac3e18f): <https://commits.webkit.org/291713@main> Reviewed commits have been landed. Closing PR #41876 and removing active labels.
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