swiftlang/swift
在 GitHub 查看[SR-7842] Inconsistent codegen for closed ranges vs bit-manipulation
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#50,378 创建于 2018年6月1日
SILOptimizerbugcompilergood first issueperformancestandard library
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描述
| Previous ID | SR-7842 |
| Radar | rdar://problem/40725067 |
| Original Reporter | @milseman |
| Type | Bug |
Attachment: Download
| Votes | 0 |
| Component/s | Compiler |
| Labels | Bug, Optimizer, Performance, StarterBug |
| Assignee | None |
| Priority | Medium |
md5: 223093f3dc3457d4c7f42d8a0e46938f
Issue Description:
ClosedRange<UInt8> demonstrates poor codegen compared to explicit bit manipulation.
@usableFromInline
func _isContinuation_bits(_ x: UInt8) -> Bool {
return x & 0b1100_0000 == 0b1000_0000
}
@usableFromInline
func _isContinuation_range(_ x: UInt8) -> Bool {
let continuation: ClosedRange<UInt8> = 0x80...0xBF
return continuation.contains(x)
}
for i in 0...UInt8.max {
guard _isContinuation_bits(i) == _isContinuation_range(i) else { fatalError("mismatch") }
}
print("done")
The code generated for _isContinuation_bits is superior:
_$S3foo20_isContinuation_bitsySbs5UInt8VF:
000000010000701c and w8, w0, #​0xc0
0000000100007020 cmp w8, #​0x80
0000000100007024 cset w0, eq
0000000100007028 ret
; endp
_$S3foo21_isContinuation_rangeySbs5UInt8VF:
000000010000702c and w8, w0, #​0xff
0000000100007030 sxtb w9, w0
0000000100007034 cmp w9, #​0x0
0000000100007038 cset w9, lt
000000010000703c cmp w8, #​0xc0
0000000100007040 cset w8, lo
0000000100007044 and w0, w9, w8
0000000100007048 ret
; endp