From a0f57c3fd0cff8b92ffb4257a6d1b56467bf30f1 Mon Sep 17 00:00:00 2001 From: Martin Möhrmann Date: Mon, 4 Jun 2018 08:24:11 +0200 Subject: cmd/compile: avoid string allocations when map key is struct or array literal MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Run-TryBot: Matthew Dempsky TryBot-Result: Gobot Gobot --- src/runtime/string.go | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'src/runtime/string.go') 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 { -- cgit v1.3-5-g9baa