Commits on Mar 28, 2023

1. Disable pathologically expensive SimplifySelectOps optimization …

   `SimplifySelectOps` is a late optimization in LLVM that attempts to
   translate `select(C, load(A), load(B))` into `load(select(C, A, B))`.
   However, in order for it to do this optimization, it needs to check that
   `C` does not depend on the result of `load(A)` or `load(B)`.
   Unfortunately (unlikely Julia and LLVM at the IR level), LLVM does not
   have a topological order of statements computed at this stage of the
   compiler, so LLVM needs to iterate through all statements in the
   function in order to perform this legality check. For large functions,
   this is extremely expensive, accounting for the majority of all
   compilation time for such functions. On the other hand, the optimization
   itself is minor, allowing at most the elision of one additional load
   (and doesn't fire particularly often, because the middle end can perform
   similar optimizations). Until there is a proper solution in LLVM, simply
   disable this optimizations, making LLVM several orders of magnitude
   faster on real world benchmarks.
   
   X-ref: llvm#60132

   

   staticfloat committed Mar 28, 2023
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