Avoid maxnum(sNaN, x) optimizations / folds (#170181) The behaviour of constant-folding `maxnum(sNaN, x)` and `minnum(sNaN, x)` has become controversial, and there are ongoing discussions about which behaviour we want to specify in the LLVM IR LangRef. See: - https://github.com/llvm/llvm-project/issues/170082 - https://github.com/llvm/llvm-project/pull/168838 - https://github.com/llvm/llvm-project/pull/138451 - https://github.com/llvm/llvm-project/pull/170067 - https://discourse.llvm.org/t/rfc-a-consistent-set-of-semantics-for-the-floating-point-minimum-and-maximum-operations/89006 This patch removes optimizations and constant-folding support for `maxnum(sNaN, x)` but keeps it folded/optimized for `qNaN`. This should allow for some more flexibility so the implementation can conform to either the old or new version of the semantics specified without any changes. As far as I am aware, optimizations involving constant `sNaN` should generally be edge-cases that rarely occur, so here should hopefully be very little real-world performance impact from disabling these optimizations.
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