Change _setindex implementation for tuples to improve constant propagation (#40635)

Author: OlivierHnt

base/tuple.jl

@@ -55,11 +55,10 @@ function setindex(x::Tuple, v, i::Integer)
     _setindex(v, i, x...)
 end
 
-function _setindex(v, i::Integer, first, tail...)
+function _setindex(v, i::Integer, args...)
     @_inline_meta
-    return (ifelse(i == 1, v, first), _setindex(v, i - 1, tail...)...)
+    return ntuple(j -> ifelse(j == i, v, args[j]), length(args))
 end
-_setindex(v, i::Integer) = ()
 
 
 ## iterating ##

test/tuple.jl

@@ -533,6 +533,9 @@ end
 
     @test Base.setindex((1, 2, 4), 4, true) === (4, 2, 4)
     @test_throws BoundsError Base.setindex((1, 2), 2, false)
+
+    f() = Base.setindex((1:1, 2:2, 3:3), 9, 1)
+    @test @inferred(f()) == (9, 2:2, 3:3)
 end
 
 @testset "inferrable range indexing with constant values" begin