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cmd/internal/obj/riscv: factor out shift constant code

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Move the code that tests to see if a constant can be represented by a
32 bit signed integer and a logical left shift. This reduces duplication
and increases readability. Also add test coverage now that this is an
independent function.

Change-Id: Id25395b1380b00cf5b69ca201b7715ef84f7ade6
Reviewed-on: https://go-review.googlesource.com/c/go/+/652777
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Joel Sing 2025-02-18 18:23:27 +11:00
parent 574e836055
commit af133d86e4
2 changed files with 86 additions and 8 deletions
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30
src/cmd/internal/obj/riscv/obj.go
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@ -135,10 +135,7 @@ func progedit(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
case AMOV:
if p.From.Type == obj.TYPE_CONST && p.From.Name == obj.NAME_NONE && p.From.Reg == obj.REG_NONE && int64(int32(p.From.Offset)) != p.From.Offset {
ctz := bits.TrailingZeros64(uint64(p.From.Offset))
val := p.From.Offset >> ctz
if int64(int32(val)) == val {
// It's ok. We can handle constants with many trailing zeros.
if isShiftConst(p.From.Offset) {
break
}
// Put >32-bit constants in memory and load them.
@ -2223,6 +2220,24 @@ func encodingForAs(as obj.As) (*encoding, error) {
return &insData.enc, nil
}
// splitShiftConst attempts to split a constant into a signed 32 bit integer
// and a corresponding left shift.
func splitShiftConst(v int64) (imm int64, lsh int, ok bool) {
lsh = bits.TrailingZeros64(uint64(v))
c := v >> lsh
if int64(int32(c)) != c {
return 0, 0, false
}
return c, lsh, true
}
// isShiftConst indicates whether a constant can be represented as a signed
// 32 bit integer that is left shifted.
func isShiftConst(v int64) bool {
_, lsh, ok := splitShiftConst(v)
return ok && lsh > 0
}
type instruction struct {
p *obj.Prog // Prog that instruction is for
as obj.As // Assembler opcode
@ -2504,10 +2519,9 @@ func instructionsForMOV(p *obj.Prog) []*instruction {
// SLLI $63, X10, X10
var insSLLI *instruction
if err := immIFits(ins.imm, 32); err != nil {
ctz := bits.TrailingZeros64(uint64(ins.imm))
if err := immIFits(ins.imm>>ctz, 32); err == nil {
ins.imm = ins.imm >> ctz
insSLLI = &instruction{as: ASLLI, rd: ins.rd, rs1: ins.rd, imm: int64(ctz)}
if c, lsh, ok := splitShiftConst(ins.imm); ok {
ins.imm = c
insSLLI = &instruction{as: ASLLI, rd: ins.rd, rs1: ins.rd, imm: int64(lsh)}
}
}