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| author | Martin Möhrmann <moehrmann@google.com> | 2018-06-04 08:24:11 +0200 |
|---|---|---|
| committer | Martin Möhrmann <moehrmann@google.com> | 2018-10-15 19:22:07 +0000 |
| commit | a0f57c3fd0cff8b92ffb4257a6d1b56467bf30f1 (patch) | |
| tree | 932804987efc8f5c0e29d9d3d4ad1b6e72ebcc02 /src/runtime/string.go | |
| parent | a1ca4893ff755d6b0b3bf4b026196d55251ea846 (diff) | |
| download | go-a0f57c3fd0cff8b92ffb4257a6d1b56467bf30f1.tar.xz | |
cmd/compile: avoid string allocations when map key is struct or array literal
x = map[string(byteslice)] is already optimized by the compiler to avoid a
string allocation. This CL generalizes this optimization to:
x = map[T1{ ... Tn{..., string(byteslice), ...} ... }]
where T1 to Tn is a nesting of struct and array literals.
Found in a hot code path that used a struct of strings made from []byte
slices to make a map lookup.
There are no uses of the more generalized optimization in the standard library.
Passes toolstash -cmp.
MapStringConversion/32/simple 21.9ns ± 2% 21.9ns ± 3% ~ (p=0.995 n=17+20)
MapStringConversion/32/struct 28.8ns ± 3% 22.0ns ± 2% -23.80% (p=0.000 n=20+20)
MapStringConversion/32/array 28.5ns ± 2% 21.9ns ± 2% -23.14% (p=0.000 n=19+16)
MapStringConversion/64/simple 21.0ns ± 2% 21.1ns ± 3% ~ (p=0.072 n=19+18)
MapStringConversion/64/struct 72.4ns ± 3% 21.3ns ± 2% -70.53% (p=0.000 n=20+20)
MapStringConversion/64/array 72.8ns ± 1% 21.0ns ± 2% -71.13% (p=0.000 n=17+19)
name old allocs/op new allocs/op delta
MapStringConversion/32/simple 0.00 0.00 ~ (all equal)
MapStringConversion/32/struct 0.00 0.00 ~ (all equal)
MapStringConversion/32/array 0.00 0.00 ~ (all equal)
MapStringConversion/64/simple 0.00 0.00 ~ (all equal)
MapStringConversion/64/struct 1.00 ± 0% 0.00 -100.00% (p=0.000 n=20+20)
MapStringConversion/64/array 1.00 ± 0% 0.00 -100.00% (p=0.000 n=20+20)
Change-Id: I483b4d84d8d74b1025b62c954da9a365e79b7a3a
Reviewed-on: https://go-review.googlesource.com/c/116275
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Diffstat (limited to 'src/runtime/string.go')
| -rw-r--r-- | src/runtime/string.go | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/src/runtime/string.go b/src/runtime/string.go index d10bd96f43..839e882cdc 100644 --- a/src/runtime/string.go +++ b/src/runtime/string.go @@ -135,7 +135,8 @@ func rawstringtmp(buf *tmpBuf, l int) (s string, b []byte) { // and otherwise intrinsified by the compiler. // // Some internal compiler optimizations use this function. -// - Used for m[string(k)] lookup where m is a string-keyed map and k is a []byte. +// - Used for m[T1{... Tn{..., string(k), ...} ...}] and m[string(k)] +// where k is []byte, T1 to Tn is a nesting of struct and array literals. // - Used for "<"+string(b)+">" concatenation where b is []byte. // - Used for string(b)=="foo" comparison where b is []byte. func slicebytetostringtmp(b []byte) string { |