Compiler still can't write if for me. M3 variant - all credits to @Ilchert

00.results.md

BenchmarkDotNet=v0.12.0, OS=Windows 10.0.18363
Intel Core i7-8750H CPU 2.20GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=3.1.100
  [Host]     : .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT
  Job-TJOYHS : .NET Core 2.2.8 (CoreCLR 4.6.28207.03, CoreFX 4.6.28208.02), X64 RyuJIT
  Job-OVZXZY : .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT

Method	Runtime	Mean	Error	StdDev	Ratio	RatioSD	Gen 0	Gen 1	Gen 2	Allocated
Simple	.NET Core 2.2	36.663 ns	0.5377 ns	0.5029 ns	1.00	0.00	0.0152	-	-	72 B
OldStyle	.NET Core 2.2	31.899 ns	0.2006 ns	0.1876 ns	0.87	0.01	0.0152	-	-	72 B
AsTask	.NET Core 2.2	42.833 ns	0.7668 ns	0.6403 ns	1.17	0.02	0.0305	-	-	144 B
AsLocal	.NET Core 2.2	39.972 ns	0.6643 ns	0.6214 ns	1.09	0.02	0.0152	-	-	72 B
M3	.NET Core 2.2	16.196 ns	0.1952 ns	0.1630 ns	0.44	0.01	0.0152	-	-	72 B
Simple	.NET Core 3.1	36.609 ns	0.8249 ns	1.1830 ns	1.00	0.00	0.0153	-	-	72 B
OldStyle	.NET Core 3.1	27.483 ns	0.2813 ns	0.2493 ns	0.75	0.03	0.0153	-	-	72 B
AsTask	.NET Core 3.1	30.320 ns	0.4179 ns	0.3909 ns	0.83	0.04	0.0306	-	-	144 B
AsLocal	.NET Core 3.1	38.721 ns	0.3611 ns	0.3201 ns	1.06	0.03	0.0153	-	-	72 B
M3	.NET Core 3.1	9.113 ns	0.1769 ns	0.1568 ns	0.25	0.01	0.0153	-	-	72 B

01.Program.cs

using System;
using System.IO;
using System.Threading.Tasks;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Jobs;
using BenchmarkDotNet.Running;

namespace TaskBench
{
    class Program
    {
        static void Main(string[] args)
        {
            BenchmarkRunner.Run<Benchmark>();
        }
    }

    [MemoryDiagnoser]
    [SimpleJob(RuntimeMoniker.NetCoreApp22)]
    [SimpleJob(RuntimeMoniker.NetCoreApp31)]
    public class Benchmark
    {
        private ValueTask<int> F() => new ValueTask<int>(42);

        [Benchmark(Baseline = true)]
        public async Task<int> Simple() => await F();
        
        [Benchmark]
        public async Task<int> OldStyle()
        {
            var f = F();
            return f.IsCompletedSuccessfully ? f.Result : await f;
        }

        [Benchmark]
        public async Task<int> AsTask() => await F().AsTask();

        [Benchmark]
        public Task<int> AsLocal()
        {
            return Do().AsTask();

            async ValueTask<int> Do() => await F();
        }
        
        [Benchmark]
        public Task<int> M3()
        {
            var vt = F();
            if(vt.IsCompletedSuccessfully)
                return Task.FromResult(vt.Result);
            return Do(vt).AsTask();
        
            async ValueTask<int> Do(ValueTask<int> valueTask)
                => await valueTask;
        }
    }
}