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package x86
import (
. "github.com/mmcloughlin/avo/build"
. "github.com/mmcloughlin/avo/operand"
"math"
"math/bits"
"github.com/segmentio/asm/cpu"
)
// JumpIfFeature constructs a jump sequence that tests for one or more feature flags.
// If all flags are matched, jump to the target label.
func JumpIfFeature(jmp string, f cpu.X86Feature) {
jump(LabelRef(jmp), f, false)
}
// JumpUnlessFeature constructs a jump sequence that tests for one or more feature flags.
// Unless all flags are matched, jump to the target label.
func JumpUnlessFeature(jmp string, f cpu.X86Feature) {
jump(LabelRef(jmp), f, true)
}
// cpuAddr is a Mem operand containing the global symbolic reference to the
// X86 cpu feature flags.
var cpuAddr = NewDataAddr(Symbol{Name: "github·com∕segmentio∕asm∕cpu·X86"}, 0)
func jump(jmp Op, f cpu.X86Feature, invert bool) {
if bits.OnesCount64(uint64(f)) == 1 {
// If the feature test is for a single flag, optimize the test using BTQ
jumpSingleFlag(jmp, f, invert)
} else {
jumpMultiFlag(jmp, f, invert)
}
}
func jumpSingleFlag(jmp Op, f cpu.X86Feature, invert bool) {
bit := U8(bits.TrailingZeros64(uint64(f)))
// Likely only need lower 4 bytes
if bit < 32 {
BTL(bit, cpuAddr)
} else {
BTQ(bit, cpuAddr)
}
if invert {
JCC(jmp)
} else {
JCS(jmp)
}
}
func jumpMultiFlag(jmp Op, f cpu.X86Feature, invert bool) {
r := GP64()
MOVQ(cpuAddr, r)
var op Op
if f <= math.MaxUint32 {
op = U32(f)
} else {
op = GP64()
MOVQ(U64(f), op)
}
ANDQ(op, r)
CMPQ(r, op)
if invert {
JNE(jmp)
} else {
JEQ(jmp)
}
}
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