2 Commits

Author	SHA1	Message	Date
Craig Topper	a63b724729	[RISCV] Use SUB instead of XOR in lowerShiftLeftParts/lowerShiftRightParts./ ... isel is now capable of turning the SUB into XOR for shift amounts. Though it uses NOT instead of XOR with ShiftSize-1. By using SUB during lowering we enable more DAG combines with other arithmetic on the shift amount.	2022-12-29 17:04:52 -08:00
Craig Topper	7cd725858b	[RISCV] RISCVDAGToDAGISel::selectShiftMask to shift by (sub size-1, X). ... If the shift amount is (sub C, X) where C is -1 modulo the size of the shift, we can replace the sub with a NOT. We could also use XORI X, size-1, but NOT would work better with c.not from the future Zce extension.	2022-12-29 16:33:18 -08:00