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## Summary This PR fixes https://github.com/llvm/llvm-project/issues/200922 - a compile-time regression affecting firstprivate clauses on simple arrays in OpenMP target regions. When `InlineHLFIRAssign` checks whether to inline `hlfir.assign` operations in `omp.private` copy regions, the alias analysis conservatively returns `MayAlias` for the copy region block arguments (`%arg0` mold vs `%arg1` private). This prevents inlining and forces a fallback to `fir.call @_FortranAAssign`, which: - Pulls in 89 runtime functions via LTO - Creates 550K+ abstract attributes in OpenMPOpt - Causes severe compile-time degradation (60%+ increase in some cases) **Example:** ```fortran !$omp target firstprivate(array) ! ... use array ... !$omp end target ``` The firstprivate copy generates an `omp.private` copy region where the assignment from the original array to the private copy cannot be inlined due to conservative aliasing assumptions. ## Root Cause and Solution The FIR alias analysis did not recognize that `omp.private` copy region block arguments are guaranteed by the OpenMP specification to reference different memory locations: - `%arg0` (mold) - the original variable - `%arg1` (private) - freshly allocated private storage created in the init region Since the private copy is allocated fresh, these arguments **cannot alias**. So, this PR adds special-case handling in `flang/lib/Optimizer/Analysis/AliasAnalysis.cpp` to recognize `omp.private` copy region block arguments and correctly return `NoAlias`. This allows `InlineHLFIRAssign` to inline the assignment into an element-wise loop, avoiding the expensive runtime call entirely. Assisted by: Claude Sonnet --------- Co-authored-by: Claude Sonnet 4 <noreply@anthropic.com> |
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