Improve RangeOps::Merge#129390
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Pull request overview
This PR tweaks RangeOps::Merge in the CoreCLR JIT range analysis to broaden when certain symbolic/constant merge rules apply, aiming to improve SPMI code size by producing tighter (or more frequently-applicable) merged ranges.
Changes:
- Relaxes the “widen upper limit” heuristic when merging a constant upper bound with a
$bnd + cnsupper bound. - Generalizes the “binop-array lower bound + constant lower bound” merge rule by removing the prior
cns <= 0gating and updating the accompanying rationale comment.
Drop the redundant `k >= 0` guard on the upper-limit widening rule Max(k, ($bnd + n)) => ($bnd + n): since $bnd >= 0 and n >= k, the result ($bnd + n) is already >= k for any sign of k, and it stays symbolic so a possible overflow is preserved. The lower-limit rule keeps its cns <= 0 guard: for cns > 0, ($bnd + cns) can overflow (e.g. a Span length is bounded by INT_MAX), so collapsing it to a constant would be an unsound (too-high) lower bound. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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PTAL @AndyAyersMS @dotnet/jit-contrib |
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Jun 15, 2026
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Fold more bound checks with up to -110k diffs
RangeOps::Merge is typically used when we merge ranges from PHI args, e,g,
[0..1] U [10..10]becomes[0..10]Note
This PR was authored with assistance from GitHub Copilot CLI (AI). The change was validated locally via SuperPMI asmdiffs.