561bf0457f
The compiler is currently zero extending 32 bit unsigned integers to
64 bits before right shifting them using a 64 bit shift instruction.
There's no need to do this as RISC-V has instructions for right
shifting 32 bit unsigned values (srlw and srliw) which zero extend
the result of the shift to 64 bits. Change the compiler so that
it uses srlw and srliw for 32 bit unsigned shifts reducing in most
cases the number of instructions needed to perform the shift.
Here are some examples of code sequences that are changed by this
patch:
uint32(a) >> 2
before:
sll x5,x10,0x20
srl x10,x5,0x22
after:
srlw x10,x10,0x2
uint32(a) >> int(b)
before:
sll x5,x10,0x20
srl x5,x5,0x20
srl x5,x5,x11
sltiu x6,x11,64
neg x6,x6
and x10,x5,x6
after:
srlw x5,x10,x11
sltiu x6,x11,32
neg x6,x6
and x10,x5,x6
bits.RotateLeft32(uint32(a), 1)
before:
sll x5,x10,0x1
sll x6,x10,0x20
srl x7,x6,0x3f
or x5,x5,x7
after:
sll x5,x10,0x1
srlw x6,x10,0x1f
or x10,x5,x6
bits.RotateLeft32(uint32(a), int(b))
before:
and x6,x11,31
sll x7,x10,x6
sll x8,x10,0x20
srl x8,x8,0x20
add x6,x6,-32
neg x6,x6
srl x9,x8,x6
sltiu x6,x6,64
neg x6,x6
and x6,x9,x6
or x6,x6,x7
after:
and x5,x11,31
sll x6,x10,x5
add x5,x5,-32
neg x5,x5
srlw x7,x10,x5
sltiu x5,x5,32
neg x5,x5
and x5,x7,x5
or x10,x6,x5
The one regression observed is the following case, an unbounded right
shift of a uint32 where the value we're shifting by is known to be
< 64 but > 31. As this is an unusual case this commit does not
optimize for it, although the existing code does.
uint32(a) >> (b & 63)
before:
sll x5,x10,0x20
srl x5,x5,0x20
and x6,x11,63
srl x10,x5,x6
after
and x5,x11,63
srlw x6,x10,x5
sltiu x5,x5,32
neg x5,x5
and x10,x6,x5
Here we have one extra instruction.
Some benchmark highlights, generated on a VisionFive2 8GB running
Ubuntu 23.04.
pkg: math/bits
LeadingZeros32-4 18.64n ± 0% 17.32n ± 0% -7.11% (p=0.000 n=10)
LeadingZeros64-4 15.47n ± 0% 15.51n ± 0% +0.26% (p=0.027 n=10)
TrailingZeros16-4 18.48n ± 0% 17.68n ± 0% -4.33% (p=0.000 n=10)
TrailingZeros32-4 16.87n ± 0% 16.07n ± 0% -4.74% (p=0.000 n=10)
TrailingZeros64-4 15.26n ± 0% 15.27n ± 0% +0.07% (p=0.043 n=10)
OnesCount32-4 20.08n ± 0% 19.29n ± 0% -3.96% (p=0.000 n=10)
RotateLeft-4 8.864n ± 0% 8.838n ± 0% -0.30% (p=0.006 n=10)
RotateLeft32-4 8.837n ± 0% 8.032n ± 0% -9.11% (p=0.000 n=10)
Reverse32-4 29.77n ± 0% 26.52n ± 0% -10.93% (p=0.000 n=10)
ReverseBytes32-4 9.640n ± 0% 8.838n ± 0% -8.32% (p=0.000 n=10)
Sub32-4 8.835n ± 0% 8.035n ± 0% -9.06% (p=0.000 n=10)
geomean 11.50n 11.33n -1.45%
pkg: crypto/md5
Hash8Bytes-4 1.486µ ± 0% 1.426µ ± 0% -4.04% (p=0.000 n=10)
Hash64-4 2.079µ ± 0% 1.968µ ± 0% -5.36% (p=0.000 n=10)
Hash128-4 2.720µ ± 0% 2.557µ ± 0% -5.99% (p=0.000 n=10)
Hash256-4 3.996µ ± 0% 3.733µ ± 0% -6.58% (p=0.000 n=10)
Hash512-4 6.541µ ± 0% 6.072µ ± 0% -7.18% (p=0.000 n=10)
Hash1K-4 11.64µ ± 0% 10.75µ ± 0% -7.58% (p=0.000 n=10)
Hash8K-4 82.95µ ± 0% 76.32µ ± 0% -7.99% (p=0.000 n=10)
Hash1M-4 10.436m ± 0% 9.591m ± 0% -8.10% (p=0.000 n=10)
Hash8M-4 83.50m ± 0% 76.73m ± 0% -8.10% (p=0.000 n=10)
Hash8BytesUnaligned-4 1.494µ ± 0% 1.434µ ± 0% -4.02% (p=0.000 n=10)
Hash1KUnaligned-4 11.64µ ± 0% 10.76µ ± 0% -7.52% (p=0.000 n=10)
Hash8KUnaligned-4 83.01µ ± 0% 76.32µ ± 0% -8.07% (p=0.000 n=10)
geomean 28.32µ 26.42µ -6.72%
Change-Id: I20483a6668cca1b53fe83944bee3706aadcf8693
Reviewed-on: https://go-review.googlesource.com/c/go/+/528975
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Gopher Robot <gobot@golang.org>
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| .github | ||
| api | ||
| doc | ||
| lib/time | ||
| misc | ||
| src | ||
| test | ||
| .gitattributes | ||
| .gitignore | ||
| codereview.cfg | ||
| CONTRIBUTING.md | ||
| go.env | ||
| LICENSE | ||
| PATENTS | ||
| README.md | ||
| SECURITY.md | ||
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