Implemented feedback.

Author: timcassell

src/BenchmarkDotNet/Engines/Engine.cs

@@ -225,7 +225,7 @@ private ClockSpan Measure(Action<long> action, long invokeCount)
             var exceptionsStats = new ExceptionsStats(); // allocates
             exceptionsStats.StartListening(); // this method might allocate
 
-            if (RuntimeInformation.IsNetCore && Environment.Version.Major is >= 3 and <= 6 && Environment.GetEnvironmentVariable("COMPlus_TieredCompilation") != "0")
+            if (RuntimeInformation.IsNetCore && Environment.Version.Major is >= 3 and <= 6 && RuntimeInformation.IsTieredJitEnabled)
             {
                 // #1542
                 // We put the current thread to sleep so tiered jit can kick in, compile its stuff,

src/BenchmarkDotNet/Engines/GcStats.cs

@@ -107,7 +107,7 @@ public int GetCollectionsCount(int generation)
             return AllocatedBytes <= AllocationQuantum ? 0L : AllocatedBytes;
         }
 
-        // Make sure tier0 jit doesn't cause any unexpected allocations in this method.
+        // Skip tier0 jit to make sure we don't get any unexpected allocations in this method.
         [MethodImpl(CodeGenHelper.AggressiveOptimizationOption)]
         public static GcStats ReadInitial()
         {
@@ -121,7 +121,7 @@ public static GcStats ReadInitial()
                 0);
         }
 
-        // Make sure tier0 jit doesn't cause any unexpected allocations in this method.
+        // Skip tier0 jit to make sure we don't get any unexpected allocations in this method.
         [MethodImpl(CodeGenHelper.AggressiveOptimizationOption)]
         public static GcStats ReadFinal()
         {
@@ -137,7 +137,7 @@ public static GcStats ReadFinal()
         public static GcStats FromForced(int forcedFullGarbageCollections)
             => new GcStats(forcedFullGarbageCollections, forcedFullGarbageCollections, forcedFullGarbageCollections, 0, 0);
 
-        // Make sure tier0 jit doesn't cause any unexpected allocations in this method.
+        // Skip tier0 jit to make sure we don't get any unexpected allocations in this method.
         [MethodImpl(CodeGenHelper.AggressiveOptimizationOption)]
         private static long? GetAllocatedBytes()
         {

src/BenchmarkDotNet/Portability/RuntimeInformation.cs

@@ -85,6 +85,18 @@ private static bool IsAotMethod()
         public static readonly bool IsAot = !System.Runtime.CompilerServices.RuntimeFeature.IsDynamicCodeCompiled;
 #endif
 
+        public static readonly bool IsTieredJitEnabled =
+            IsNetCore
+            && (Environment.Version.Major < 3
+                // Disabled by default in netcoreapp2.X, check if it's enabled.
+                ? Environment.GetEnvironmentVariable("COMPlus_TieredCompilation") == "1"
+                || Environment.GetEnvironmentVariable("DOTNET_TieredCompilation") == "1"
+                || (AppContext.TryGetSwitch("System.Runtime.TieredCompilation", out bool isEnabled) && isEnabled)
+                // Enabled by default in netcoreapp3.0+, check if it's disabled.
+                : Environment.GetEnvironmentVariable("COMPlus_TieredCompilation") != "0"
+                && Environment.GetEnvironmentVariable("DOTNET_TieredCompilation") != "0"
+                && (!AppContext.TryGetSwitch("System.Runtime.TieredCompilation", out isEnabled) || isEnabled));
+
         public static bool IsRunningInContainer => string.Equals(Environment.GetEnvironmentVariable("DOTNET_RUNNING_IN_CONTAINER"), "true");
 
         internal static string ExecutableExtension => IsWindows() ? ".exe" : string.Empty;