add a test

Author: majocha

tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj

@@ -351,6 +351,7 @@
     <Compile Include="FSharpChecker\TransparentCompiler.fs" />
     <Compile Include="FSharpChecker\SymbolUse.fs" />
     <Compile Include="FSharpChecker\FindReferences.fs" />
+    <Compile Include="Optimizer\NestedApplications.fs" />
     <Compile Include="Attributes\AttributeCtorSetPropAccess.fs" />
   </ItemGroup>
 

tests/FSharp.Compiler.ComponentTests/Optimizer/NestedApplications.fs

@@ -0,0 +1,64 @@
+namespace FSharp.Compiler.ComponentTests.Optimizer
+
+open System.Text
+open Xunit
+open FSharp.Test
+open FSharp.Test.Compiler
+open FSharp.Test.Utilities
+
+module private Gen =
+    let nestedLetApps depth =
+        // Builds: let v1 = id 0 in let v2 = id v1 in ... in ignore vN
+        let sb = StringBuilder()
+        sb.AppendLine("module M")       |> ignore
+        sb.AppendLine("let id x = x")   |> ignore
+        sb.AppendLine("let run () =")   |> ignore
+        for i in 1 .. depth do
+            if i = 1 then
+                sb.Append("    let v1 = id 0") |> ignore
+            else
+                sb.Append(" in let v").Append(i).Append(" = id v").Append(i-1) |> ignore
+        sb.AppendLine(" in ()") |> ignore
+        sb.ToString()
+
+    let nestedDirectApps depth =
+        // Builds: let res = id(id(id(...(0)))) in ignore res
+        let sb = StringBuilder()
+        sb.AppendLine("module N")       |> ignore
+        sb.AppendLine("let id x = x")   |> ignore
+        sb.Append("let run () = let res = ") |> ignore
+        for _ in 1 .. depth do
+            sb.Append("id (") |> ignore
+        sb.Append("0") |> ignore
+        for _ in 1 .. depth do
+            sb.Append(")")   |> ignore
+        sb.AppendLine(" in ignore res") |> ignore
+        sb.ToString()
+
+[<Collection(nameof NotThreadSafeResourceCollection)>]
+type ``Nested application optimizer``() =
+
+    // Moderate depths to keep CI stable while still exercising the quadratic shapes
+    [<Theory>]
+    [<InlineData(100)>]
+    [<InlineData(1000)>]
+    let ``let-chains of nested apps compile under --optimize+`` depth =
+        let src = Gen.nestedLetApps depth
+        FSharp src
+        |> withOptions [ "--optimize+"; "--times" ]
+        |> asExe
+        |> ignoreWarnings
+        |> compile
+        |> shouldSucceed
+
+    [<Theory>]
+    [<InlineData(100)>]
+    [<InlineData(1000)>]
+    let ``direct nested application compiles under --optimize+`` depth =
+        let src = Gen.nestedDirectApps depth
+        FSharp src
+        |> withOptions [ "--optimize+"; "--times" ]
+        |> asExe
+        |> ignoreWarnings
+        |> compile
+        |> shouldSucceed