release/21.x: [MachinePipeliner] Limit the number of stores in BB (#154940) #162639
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The dependency analysis in MachinePipeliner checks dependencies for every pair of store instructions in the target basic block. This means the time complexity of the analysis is `O(N^2)`, where `N` is the number of store instructions. Therefore, compilation time can become significantly long when there are too many store instructions. To mitigate it, this patch introduces logic to count the number of store instructions at the beginning of the pipeliner and bail out if it exceeds the threshold. The default value if the threshold should be large enough. Thus, in most practical cases where the pipeliner is beneficial, this patch should not cause any performance regression. Related issue: llvm#150262 (cherry picked from commit 22b79fb)
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@aankit-ca What do you think about merging this PR to the release branch? |
aankit-ca
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Oct 10, 2025
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moved this from Needs Triage
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generally seems ok, but I noticed there's no tests on the original PR, was this missed or were any added later? |
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I think we missed the testcase here, @kasuga-fj Can you please add a small testcase on this PR and also on main too? |
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Ah, sorry, that is my silly mistake. Thanks for catching it, I'll submit a PR to add a testcase on main, and request backporting after it's merged. |
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Backport 22b79fb
Requested by: @kasuga-fj