Fix SkipStages narrowing loaded by Select condition#9152
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SkipStages::visit(Select) was combining each branch's `loaded` predicate with the select condition (via make_select / make_and). That's wrong: Halide's Select evaluates both branches and only picks one of the results, so any load inside either branch fires unconditionally. The `loaded` predicate must be the OR of both branches, ungated by the condition. The bug caused allocation bounds inference to size affected buffers down to zero whenever the runtime condition was false, while the generated code still emitted a vectorized load from them -- a heap OOB read that showed up intermittently as a valgrind use-after-free on the truncated_pyramid test. Keep `used` gated by the condition as before (with the same select/and collapse that fixed the exponential blow-up in #9147). Add a regression test in skip_stages.cpp that records the minimum producer allocation size through a custom malloc handler and verifies it's non-zero when the producer's only consumer is inside a runtime-false select branch. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #9152 +/- ##
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Coverage ? 69.35%
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Files ? 254
Lines ? 78219
Branches ? 18714
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Hits ? 54248
Misses ? 18481
Partials ? 5490 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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#9147 contained a bug: It treated Select like an if-then-else and combined the used and loaded flags in the same way. A select evaluates both sides, so the two flags need to be handled differently. This PR fixes it and adds a regression test. This is the cause of the recent failures in truncated_pyramid test - it has a Func which is loaded but not used.