Ruby

string.c: Optimize String#concat when argc is 1

Optimize performance regression introduced in r56021.

• Benchmark (i7-4790K @ 4.00GH, x86_64 GNU/Linux)

Benchmark.ips do |x|
x.report("String#concat (1)") { "a".concat("b") }
if RUBY_VERSION >= "2.4.0"
x.report("String#concat (2)") { "a".concat("b", "c") }
end
end

• Ruby 2.3

Calculating -------------------------------------
String#concat (1) 6.003M (± 5.2%) i/s - 30.122M in 5.031646s

• Ruby 2.4 (Before this patch)

Calculating -------------------------------------
String#concat (1) 4.458M (± 8.9%) i/s - 22.298M in 5.058084s
String#concat (2) 3.660M (± 5.6%) i/s - 18.314M in 5.020527s

• Ruby 2.4 (After this patch)

Calculating -------------------------------------
String#concat (1) 6.448M (± 5.2%) i/s - 32.215M in 5.010833s
String#concat (2) 3.633M (± 9.0%) i/s - 18.056M in 5.022603s

[fix GH-1631]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58886 b2dd03c8-39d4-4d8f-98ff-823fe69b080e