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cmd/internal/obj/riscv: implement better bit pattern encoding

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Replace the extractBitAndShift function with an encodeBitPattern function.
This allows the caller to specify a slice of bits that are to be extracted
and encoded, rather than making multiple function calls and combining the
results.

Change-Id: I3d51caa10ecf714f2ad2fb66d38376202c4e0628
Reviewed-on: https://go-review.googlesource.com/c/go/+/702397
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Mark Ryan <markdryan@rivosinc.com>
Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Joel Sing 2025-09-10 01:16:00 +10:00
parent abb241a789
commit a15d036ce2
1 changed files with 12 additions and 23 deletions
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35
src/cmd/internal/obj/riscv/obj.go
View file

@ -1422,10 +1422,16 @@ func validateRaw(ctxt *obj.Link, ins *instruction) {
wantImmU(ctxt, ins, ins.imm, 32)
}
// extractBitAndShift extracts the specified bit from the given immediate,
// before shifting it to the requested position and returning it.
func extractBitAndShift(imm uint32, bit, pos int) uint32 {
return ((imm >> bit) & 1) << pos
// encodeBitPattern encodes an immediate value by extracting the specified
// bit pattern from the given immediate. Each value in the pattern specifies
// the position of the bit to extract from the immediate, which are then
// encoded in sequence.
func encodeBitPattern(imm uint32, pattern []int) uint32 {
outImm := uint32(0)
for _, bit := range pattern {
outImm = outImm<<1 | (imm>>bit)&1
}
return outImm
}
// encodeR encodes an R-type RISC-V instruction.
@ -1650,31 +1656,14 @@ func encodeJ(ins *instruction) uint32 {
// encodeCBImmediate encodes an immediate for a CB-type RISC-V instruction.
func encodeCBImmediate(imm uint32) uint32 {
// Bit order - [8|4:3|7:6|2:1|5]
bits := extractBitAndShift(imm, 8, 7)
bits |= extractBitAndShift(imm, 4, 6)
bits |= extractBitAndShift(imm, 3, 5)
bits |= extractBitAndShift(imm, 7, 4)
bits |= extractBitAndShift(imm, 6, 3)
bits |= extractBitAndShift(imm, 2, 2)
bits |= extractBitAndShift(imm, 1, 1)
bits |= extractBitAndShift(imm, 5, 0)
bits := encodeBitPattern(imm, []int{8, 4, 3, 7, 6, 2, 1, 5})
return (bits>>5)<<10 | (bits&0x1f)<<2
}
// encodeCJImmediate encodes an immediate for a CJ-type RISC-V instruction.
func encodeCJImmediate(imm uint32) uint32 {
// Bit order - [11|4|9:8|10|6|7|3:1|5]
bits := extractBitAndShift(imm, 11, 10)
bits |= extractBitAndShift(imm, 4, 9)
bits |= extractBitAndShift(imm, 9, 8)
bits |= extractBitAndShift(imm, 8, 7)
bits |= extractBitAndShift(imm, 10, 6)
bits |= extractBitAndShift(imm, 6, 5)
bits |= extractBitAndShift(imm, 7, 4)
bits |= extractBitAndShift(imm, 3, 3)
bits |= extractBitAndShift(imm, 2, 2)
bits |= extractBitAndShift(imm, 1, 1)
bits |= extractBitAndShift(imm, 5, 0)
bits := encodeBitPattern(imm, []int{11, 4, 9, 8, 10, 6, 7, 3, 2, 1, 5})
return bits << 2
}