work around a splatting penalty in twiceprecision (#29060)

* work around a splatting penalty in twiceprecision

* add allocation test

(cherry picked from commit 88d536a)

Author: KristofferC

base/twiceprecision.jl

@@ -332,11 +332,14 @@ const F_or_FF = Union{AbstractFloat, Tuple{AbstractFloat,AbstractFloat}}
 asF64(x::AbstractFloat) = Float64(x)
 asF64(x::Tuple{AbstractFloat,AbstractFloat}) = Float64(x[1]) + Float64(x[2])
 
+# Defined to prevent splatting in the function below which here has a performance impact
+_TP(x) = TwicePrecision{Float64}(x)
+_TP(x::Tuple{Any, Any}) = TwicePrecision{Float64}(x[1], x[2])
 function steprangelen_hp(::Type{Float64}, ref::F_or_FF,
                          step::F_or_FF, nb::Integer,
                          len::Integer, offset::Integer)
-    StepRangeLen(TwicePrecision{Float64}(ref...),
-                 twiceprecision(TwicePrecision{Float64}(step...), nb), Int(len), offset)
+    StepRangeLen(_TP(ref),
+                 twiceprecision(_TP(step), nb), Int(len), offset)
 end
 
 function steprangelen_hp(::Type{T}, ref::F_or_FF,

test/ranges.jl

@@ -1371,3 +1371,10 @@ end # module NonStandardIntegerRangeTest
         end
     end
 end
+
+@testset "allocation of TwicePrecision call" begin
+    0:286.493442:360
+    0:286:360
+    @test @allocated(0:286.493442:360) == 0
+    @test @allocated(0:286:360) == 0
+end