[all-commits] [llvm/llvm-project] 80bdfc: [LoopUtils] Don't wrap in getLoopEstimatedTripCoun...

[Ramkumar Ramachandra via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 80bdfcd411cd8197b0a8b6139b89a87d3a4528fa
      https://github.com/llvm/llvm-project/commit/80bdfcd411cd8197b0a8b6139b89a87d3a4528fa
  Author: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
  Date:   2025-03-04 (Tue, 04 Mar 2025)

  Changed paths:
    M llvm/include/llvm/Transforms/Utils/LoopUtils.h
    M llvm/lib/Transforms/Utils/LoopPeel.cpp
    M llvm/lib/Transforms/Utils/LoopUtils.cpp
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    M llvm/test/Transforms/LoopVectorize/AArch64/interleave_count_for_estimated_tc.ll
    M llvm/test/Transforms/LoopVectorize/AArch64/low_trip_memcheck_cost.ll

  Log Message:
  -----------
  [LoopUtils] Don't wrap in getLoopEstimatedTripCount (#129080)

getLoopEstimatedTripCount returns the trip count based on profiling
data, and its documentation says that it could return 0 when the trip
count is zero, but this is not the case: a valid trip count can never be
zero, and it returns 0 when the unsigned ExitCount is incremented by 1
and wraps. Some callers are careful about checking for this zero value
in an std::optional, but it makes for an API with footguns, as a
std::optional return value indicates that a non-nullopt value would be a
valid trip count. Fix this by explicitly returning std::nullopt when the
return value would wrap, and strip additional checks in callers. This
also fixes a minor bug in LoopVectorize.



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