Fix edge likelihoods out of optimize bools#131356
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Pull request overview
This PR fixes edge-likelihood propagation when optOptimizeCompareChainCondBlock merges two consecutive conditional blocks into a single compare-chain condition, ensuring the resulting block’s outgoing edge likelihoods preserve the original control-flow probabilities (including the “shared target” case).
Changes:
- Capture the pre-merge likelihoods for
b1’s removed and fallthrough edges and use them to recomputeb2’s outgoing edge likelihoods as unconditional probabilities after compaction. - Adjust
b2’s profile weight prior tofgCompactBlockso the merged block inherits the correct weight without incorrectly decrementing the shared-target’s weight. - Remove the prior call to
fgRepairProfileCondToUncond(which is tailored for true removal of alternate flow) in favor of this targeted repair for the compare-chain merge shape.
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/azp run runtime-coreclr superpmi-diffs |
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Optimize bools could produce incorrect edge likelihoods.
From the bug, we'd combine (note BB03->BB06 likelihood of 0.96):
------------ BB03 [0002] [016..022) -> BB06(0.9697322),BB04(0.03026775) (cond), preds={BB02} succs={BB04,BB06} ------------ BB04 [0003] [022..02B) -> BB06(0),BB05(1) (cond), preds={BB03} succs={BB05,BB06}into this after fusing BB003,04 (Note BB03->BB06 likelihood of 0)
------------ BB03 [0002] [016..02B) -> BB06(0),BB05(1) (cond), preds={BB02} succs={BB05,BB06}Fix
optOptimizeCompareChainCondBlockto correct this likelihood.I also replaced the call to fgRepairProfileCondToUncond which would incorrectly decrease the profile weight of BB06 in the above example.
Spent a bit looking through diffs. Regressions and improvements in perfscore are due to block weight inside loops now being calculated correctly. Some codesize changes caused by block reordering changes, as blockweight has gone 0.00->0.01 in some examples.
fixes #130150