JIT: Improve side effect detection in loop hoisting #118463
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Pull Request Overview
This PR improves side effect detection during loop hoisting by making the traversal more flow-sensitive. Previously, the JIT was overly conservative, assuming every block after the loop header could execute after the first global side effect. The new approach propagates side effect state through the control flow paths of the loop, enabling more precise hoisting decisions.
Key changes:
- Replaced global
m_beforeSideEffectflag with per-block side effect tracking usingm_sideEffectBlocksBitVec - Modified side effect detection to propagate through control flow rather than assuming worst-case after first block
- Updated comments to reflect the new flow-sensitive approach
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch |
This reverts commit 217d6e7.
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Addresses some of the regressions in #116486 and #116754. Hoisting's traversal of the loop body was previously not sensitive to execution flow, so it was overly conservative in its side effect detection, operating under the assumption that every block after the loop header could execute after the first global side effect. Now that hoisting visits loop blocks in RPO, we can propagate side effect state through the side-effecting paths of the loop.