It is one less dependent load away, and right next to another
field in the itab we also load as part of the type switch or
type assert.
Change-Id: If7aaa7814c47bd79a6c7ed4232ece0bc1d63550e
Reviewed-on: https://go-review.googlesource.com/c/go/+/533117
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
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This is the last of the getitab users to receive a cache.
We should now no longer see getitab (and callees) in profiles.
Hopefully.
Change-Id: I2ed72b9943095bbe8067c805da7f08e00706c98c
Reviewed-on: https://go-review.googlesource.com/c/go/+/531055
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
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That way we don't need to call into the runtime for every
type assertion (to an interface type).
name old time/op new time/op delta
TypeAssert-24 3.78ns ± 3% 1.00ns ± 1% -73.53% (p=0.000 n=10+8)
Change-Id: I0ba308aaf0f24a5495b4e13c814d35af0c58bfde
Reviewed-on: https://go-review.googlesource.com/c/go/+/529316
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That way we don't need to call into the runtime when the type being
switched on has been seen many times before.
The cache is just a hash table of a sample of all the concrete types
that have been switched on at that source location. We record the
matching case number and the resulting itab for each concrete input
type.
The caches seldom get large. The only two in a run of all.bash that
get more than 100 entries, even with the sampling rate set to 1, are
test/fixedbugs/issue29264.go, with 101
test/fixedbugs/issue29312.go, with 254
Both happen at the type switch in fmt.(*pp).handleMethods, perhaps
unsurprisingly.
name old time/op new time/op delta
SwitchInterfaceTypePredictable-24 25.8ns ± 2% 2.5ns ± 3% -90.43% (p=0.000 n=10+10)
SwitchInterfaceTypeUnpredictable-24 37.5ns ± 2% 11.2ns ± 1% -70.02% (p=0.000 n=10+10)
Change-Id: I4961ac9547b7f15b03be6f55cdcb972d176955eb
Reviewed-on: https://go-review.googlesource.com/c/go/+/526658
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
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Reviewed-by: Keith Randall <khr@google.com>
For type switches where the targets are interface types,
call into the runtime once instead of doing a sequence
of assert* calls.
name old time/op new time/op delta
SwitchInterfaceTypePredictable-24 26.6ns ± 1% 25.8ns ± 2% -2.86% (p=0.000 n=10+10)
SwitchInterfaceTypeUnpredictable-24 39.3ns ± 1% 37.5ns ± 2% -4.57% (p=0.000 n=10+10)
Not super helpful by itself, but this code organization allows
followon CLs that add caching to the lookups.
Change-Id: I7967f85a99171faa6c2550690e311bea8b54b01c
Reviewed-on: https://go-review.googlesource.com/c/go/+/526657
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For large interface -> concrete type switches, we can use a jump
table on some bits of the type hash instead of a binary search on
the type hash.
name old time/op new time/op delta
SwitchTypePredictable-24 1.99ns ± 2% 1.78ns ± 5% -10.87% (p=0.000 n=10+10)
SwitchTypeUnpredictable-24 11.0ns ± 1% 9.1ns ± 2% -17.55% (p=0.000 n=7+9)
Change-Id: Ida4768e5d62c3ce1c2701288b72664aaa9e64259
Reviewed-on: https://go-review.googlesource.com/c/go/+/521497
Reviewed-by: Keith Randall <khr@google.com>
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Currently we use a full cmpstring to do the comparison for each
split in the binary search for a string switch.
Instead, split by comparing a single byte of the input string with a
constant. That will give us a much faster split (although it might be
not quite as good a split).
Fixes#53333
R=go1.20
Change-Id: I28c7209342314f367071e4aa1f2beb6ec9ff7123
Reviewed-on: https://go-review.googlesource.com/c/go/+/414894
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When compiling expression switches, we try to optimize runs of
constants into binary searches. The ordering used isn't visible to the
application, so it's unimportant as long as we're consistent between
sorting and searching.
For strings, it's much cheaper to compare string lengths than strings
themselves, so instead of ordering strings by "si <= sj", we currently
order them by "len(si) < len(sj) || len(si) == len(sj) && si <= sj"
(i.e., the lexicographical ordering on the 2-tuple (len(s), s)).
However, it's also somewhat cheaper to compare strings for equality
(i.e., ==) than for ordering (i.e., <=). And if there were two or
three string constants of the same length in a switch statement, we
might unnecessarily emit ordering comparisons.
For example, given:
switch s {
case "", "1", "2", "3": // ordered by length then content
goto L
}
we currently compile this as:
if len(s) < 1 || len(s) == 1 && s <= "1" {
if s == "" { goto L }
else if s == "1" { goto L }
} else {
if s == "2" { goto L }
else if s == "3" { goto L }
}
This CL switches to using a 2-level binary search---first on len(s),
then on s itself---so that string ordering comparisons are only needed
when there are 4 or more strings of the same length. (4 being the
cut-off for when using binary search is actually worthwhile.)
So the above switch instead now compiles to:
if len(s) == 0 {
if s == "" { goto L }
} else if len(s) == 1 {
if s == "1" { goto L }
else if s == "2" { goto L }
else if s == "3" { goto L }
}
which is better optimized by walk and SSA. (Notably, because there are
only two distinct lengths and no more than three strings of any
particular length, this example ends up falling back to simply using
linear search.)
Test case by khr@ from CL 195138.
Fixes#33934.
Change-Id: I8eeebcaf7e26343223be5f443d6a97a0daf84f07
Reviewed-on: https://go-review.googlesource.com/c/go/+/195340
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
