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[X86] Add slow div64 tuning flag to Nehalem target (#91129) This appears to have been missed because later cpus don't inherit from Nehalem tuning much. Noticed while cleaning up for #90985 Merge commit 8b400de79eff from llvm-project (by Simon Pilgrim): [X86] Enable TuningSlowDivide64 on Barcelona/Bobcat/Bulldozer/Ryzen Families (#91277) Despite most AMD cpus having a lower latency for i64 divisions that converge early, we are still better off testing for values representable as i32 and performing a i32 division if possible. All AMD cpus appear to have been missed when we added the "idivq-to-divl" attribute - this patch now matches Intel cpu behaviour (and the x86-64/v2/3/4 levels). Unfortunately the difference in code scheduling means I've had to stop using the update_llc_test_checks script and just use old-fashioned CHECK-DAG checks for divl/divq pairs. Fixes #90985 This fixes possibly worse runtime performance on AMD Zen hardware, when using -march=znver4 (or any other znver), as opposed to -march=x86-64-v4 or the baseline -march=x86-64. A similar fix is applied for Nehalem. PR: 278908 MFC after: 3 days |
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