[JSC] DFGLoopUnrollingPhase: Enforce tail and exit block unification for safe unrolling#43925
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r=me if you ensure that this does not break the existing cases in JS2.
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…for safe unrolling https://bugs.webkit.org/show_bug.cgi?id=291393 rdar://149023954 Reviewed by Yusuke Suzuki. This patch tightens the eligibility criteria for loop unrolling by requiring that the loop tail (block that branches back to the header) and the loop exit block (block that exits the loop) must be the same. This restriction ensures the loop follows a simple and well-structured control flow pattern, making it safe for full unrolling without introducing correctness issues or complex edge handling. Specifically: 1. Identifies the tail block by looking for a unique predecessor of the header that dominates it. 2. Identifies the exit block as a loop body block with a successor outside the loop. 3. Skips unrolling if multiple tails, multiple exits, or mismatched tail and exit blocks are found. This change is a preparatory step for broader loop unrolling support in the future. * Source/JavaScriptCore/dfg/DFGLoopUnrollingPhase.cpp: (JSC::DFG::LoopUnrollingPhase::locateTail): Canonical link: https://commits.webkit.org/293588@main
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Committed 293588@main (1eb0a41): https://commits.webkit.org/293588@main Reviewed commits have been landed. Closing PR #43925 and removing active labels. |
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