• Martin Möhrmann's avatar
    cmd/compile: avoid string allocations when map key is struct or array literal · a0f57c3f
    Martin Möhrmann authored
    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/116275Reviewed-by: 's avatarMatthew Dempsky <mdempsky@google.com>
    Run-TryBot: Matthew Dempsky <mdempsky@google.com>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    a0f57c3f
string.go 10.7 KB