[AArch64][NEON] Extend faminmax patterns with fminnm/fmaxnm (#104766) Patterns were previously added to allow the following reductions - fminimum(abs(a), abs(b)) -> famin(a, b) - fmaximum(abs(a), abs(b)) -> famax(a, b) - https://github.com/llvm/llvm-project/pull/103027 It was suggested by @davemgreen that the following reductions are also possible - fminnum[nnan](abs(a), abs(b)) -> famin(a, b) - fmaxnum[nnan](abs(a), abs(b)) -> famax(a, b) ('nnan' documenatation: https://llvm.org/docs/LangRef.html#fast-math-flags) The 'no NaNs' flag allows optimisations to assume that neither argument is a NaN, and so the differing NaN propagation semantics of llvm.maxnum/llvm.minnum and FAMAX/FAMIN can be ignored in this reduction. (llvm.maxnum/llvm.minnum: https://llvm.org/docs/LangRef.html#llvm-minnum-intrinsic) - Changes to LLVM - lib/target/AArch64/AArch64InstrInfo.td - add 'fminnm_nnan' and 'fmaxnm_nnan'; patfrags on fminnm/fmaxnm that are predicated on the instrinsic call having the 'nnan' flag. - add AArch64famin and AArch64famax patfrags, containing the new and existing reductions. - test/CodeGen/AArch64/aarch64-neon-faminmax.ll - add positive and negative tests for the new reduction, based on the presence of 'nnan' in the IR intrinsic call.
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