improve performance for string(...) (JuliaLang#28876)

* improve performance for various string methods

base/strings/io.jl

@@ -103,31 +103,43 @@ function sprint(f::Function, args...; context=nothing, sizehint::Integer=0)
  String(resize!(s.data, s.size))
 end
 
-tostr_sizehint(x) = 0
+tostr_sizehint(x) = 8
 tostr_sizehint(x::AbstractString) = lastindex(x)
 tostr_sizehint(x::Float64) = 20
 tostr_sizehint(x::Float32) = 12
 
-function print_to_string(xs...; env=nothing)
+function print_to_string(xs...)
  if isempty(xs)
  return ""
  end
+ siz = 0
+ for x in xs
+ siz += tostr_sizehint(x)
+ end
  # specialized for performance reasons
- s = IOBuffer(sizehint=tostr_sizehint(xs[1]))
- if env !== nothing
- env_io = IOContext(s, env)
- for x in xs
- print(env_io, x)
- end
- else
- for x in xs
- print(s, x)
- end
+ s = IOBuffer(sizehint=siz)
+ for x in xs
+ print(s, x)
  end
  String(resize!(s.data, s.size))
 end
 
-string_with_env(env, xs...) = print_to_string(xs...; env=env)
+function string_with_env(env, xs...)
+ if isempty(xs)
+ return ""
+ end
+ siz = 0
+ for x in xs
+ siz += tostr_sizehint(x)
+ end
+ # specialized for performance reasons
+ s = IOBuffer(sizehint=siz)
+ env_io = IOContext(s, env)
+ for x in xs
+ print(env_io, x)
+ end
+ String(resize!(s.data, s.size))
+end
 
 """
  string(xs...)

base/strings/substring.jl

@@ -142,19 +142,32 @@ function reverse(s::Union{String,SubString{String}})::String
  end
 end
 
-function string(a::Union{String, SubString{String}}...)
- if length(a) == 1
- return String(a[1])
- end
+string(a::String) = String(a)
+string(a::SubString{String}) = String(a)
+
+function string(a::Union{Char, String, SubString{String}}...)
  n = 0
- for str in a
- n += sizeof(str)
+ for v in a
+ if v isa Char
+ n += codelen(v)
+ else
+ n += sizeof(v)
+ end
  end
  out = _string_n(n)
  offs = 1
- for str in a
- unsafe_copyto!(pointer(out,offs), pointer(str), sizeof(str))
- offs += sizeof(str)
+ for v in a
+ if v isa Char
+ x = bswap(reinterpret(UInt32, v))
+ for j in 1:codelen(v)
+ unsafe_store!(pointer(out, offs), x % UInt8)
+ offs += 1
+ x >>= 8
+ end
+ else
+ unsafe_copyto!(pointer(out,offs), pointer(v), sizeof(v))
+ offs += sizeof(v)
+ end
  end
  return out
 end

test/strings/basic.jl

@@ -34,6 +34,7 @@ using Random
  @test string("∀∃", "1∀∃") === "∀∃1∀∃"
  @test string(SubString("∀∃"), SubString("1∀∃", 2)) === "∀∃∀∃"
  @test string(s"123") === s"123"
+ @test string("123", 'α', SubString("1∀∃", 2), 'a', "foo") === "123α∀∃afoo"
  codegen_egal_of_strings(x, y) = (x===y, x!==y)
  @test codegen_egal_of_strings(string("ab", 'c'), "abc") === (true, false)
  let strs = ["", "a", "a b c", "до свидания"]