[X86] combineVTRUNCSAT - attempt to recognise VTRUNCS/US(CONCAT(X,Y)) -> PACKSS/US(X,Y) folds. #178707
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… -> PACKSS/US(X,Y) folds. If we're just concatenating subvectors together to perform a saturated truncate, see if we can perform PACK on the subvectors directly instead - 256-bit PACK will require a post-shuffle, but this will typically fold away in later shuffle combining and its probably better than changing vector widths with concats. Reference patch based off poor codegen identified in llvm#169995
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If we're just concatenating subvectors together to perform a saturated truncate, see if we can perform PACK on the subvectors directly instead - 256-bit PACK will require a post-shuffle, but this will typically fold away in later shuffle combining and its probably better than changing vector widths with concats.
Reference patch based off poor codegen identified in #169995