Benchmark the cost of copying BuiltinContext passed to function vs not doing it

copy_cost_test.go

func BenchmarkBuiltinContextCopyCost(b *testing.B) {
	b.Run("withBctx", func(b *testing.B) {
		b.ResetTimer()
		b.ReportAllocs()

		for range b.N {
			bctx := BuiltinContext{}

			withBctx(bctx, "bctx")
		}
	})

	b.Run("withBctxPointer", func(b *testing.B) {
		b.ResetTimer()
		b.ReportAllocs()

		for range b.N {
			withBctxPointer(nil, "bctx")
		}
	})

	b.Run("withoutBctx", func(b *testing.B) {
		b.ResetTimer()
		b.ReportAllocs()

		for range b.N {
			withoutBctx("bctx")
		}
	})
}

//go:noinline
func withBctx(_ BuiltinContext, s string) {
	if s != "bctx" {
		panic("bctx should not be used in this test")
	}
}

//go:noinline
func withBctxPointer(_ *BuiltinContext, s string) {
	if s != "bctx" {
		panic("bctx should not be used in this test")
	}
}

//go:noinline
func withoutBctx(s string) {
	if s != "bctx" {
		panic("bctx should not be used in this test")
	}
}

gistfile1.txt

goos: darwin
goarch: arm64
pkg: github.com/open-policy-agent/opa/v1/topdown
cpu: Apple M4 Pro
BenchmarkBuiltinContextCopyCost/withBctx-12         	307583601	         3.834 ns/op	       0 B/op	       0 allocs/op
BenchmarkBuiltinContextCopyCost/withBctxPointer-12  	1000000000	         0.9629 ns/op	       0 B/op	       0 allocs/op
BenchmarkBuiltinContextCopyCost/withoutBctx-12      	1000000000	         0.9621 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/open-policy-agent/opa/v1/topdown	4.103s