The fshl and fshr intrinsics are defined to modulo their shift amount by the bitwidth of one of their inputs. The FSR/FSL instructions read one extra bit from the shift amount. If that bit is set the inputs are swapped. In order to preserve the semantics of the llvm intrinsics we need to make sure that the extra bit isn't set. DAG combine or instcombine may have removed any mask that was originally present.
We could be smarter here and try to use computeKnownBits to check if the bit is known zero, but wanted to start with correctness.
Differential Revision: https://reviews.llvm.org/D90905
There is no FSLI instruction, but we can emulate it using FSRI by swapping operands and subtracting the immediate from the bitwidth.
Differential Revision: https://reviews.llvm.org/D90826
fsl/fsr take their shift amount in $rs2 or an immediate. The
sources are $rs1 and $rs3.
fshl/fshr ISD opcodes both concatenate operand 0 in the high bits and
operand 1 in the lower bits. fshl returns the high bits after
shifting and fshr returns the low bits. So a shift amount of 0
returns operand 0 for fshl and operand 1 for fshr.
fsl/fsr concatenate their operands in different orders such that
$rs1 will be returned for a shift amount of 0. So $rs1 needs to
come from operand 0 of fshl and operand 1 of fshr.
Differential Revision: https://reviews.llvm.org/D90735
Based on a discussion on D88783, if we're promoting a funnel shift to a width at least twice the size as the original type, then we can use the 'double shift' patterns (shifting the concatenated sources).
Differential Revision: https://reviews.llvm.org/D89139
In SelectionDAGBuilder always translate the fshl and fshr intrinsics to
FSHL and FSHR (or ROTL and ROTR) instead of lowering them to shifts and
ORs. Improve the legalization of FSHL and FSHR to avoid code quality
regressions.
Differential Revision: https://reviews.llvm.org/D77152
This patch provides optimization of bit manipulation operations by
enabling the +experimental-b target feature.
It adds matching of single block patterns of instructions to specific
bit-manip instructions from the ternary subset (zbt subextension) of the
experimental B extension of RISC-V.
It adds also the correspondent codegen tests.
This patch is based on Claire Wolf's proposal for the bit manipulation
extension of RISCV:
https://github.com/riscv/riscv-bitmanip/blob/master/bitmanip-0.92.pdf
Differential Revision: https://reviews.llvm.org/D79875
Craig Topper