JIT: Fix constrained call dereferences happening too early

src/coreclr/jit/importercalls.cpp

@@ -884,7 +884,21 @@ var_types Compiler::impImportCall(OPCODE                  opcode,
     }
 
     //-------------------------------------------------------------------------
-    // The main group of arguments
+    // The main group of arguments, and the this pointer.
+
+    // 'this' is pushed on the IL stack before all call args, but if this is a
+    // constrained call 'this' is a byref that may need to be dereferenced.
+    // That dereference should happen _after_ all args, so we need to spill
+    // them if they can interfere.
+    bool hasThis;
+    hasThis = ((mflags & CORINFO_FLG_STATIC) == 0) && ((sig->callConv & CORINFO_CALLCONV_EXPLICITTHIS) == 0) &&
+              ((opcode != CEE_NEWOBJ) || (newobjThis != nullptr));
+
+    if (hasThis && (constraintCallThisTransform == CORINFO_DEREF_THIS))
+    {
+        impSpillSideEffects(false, CHECK_SPILL_ALL DEBUGARG(
+                                       "constrained call requires dereference for 'this' right before call"));
+    }
 
     impPopCallArgs(sig, call->AsCall());
     if (extraArg.Node != nullptr)
@@ -904,8 +918,7 @@ var_types Compiler::impImportCall(OPCODE                  opcode,
     //-------------------------------------------------------------------------
     // The "this" pointer
 
-    if (((mflags & CORINFO_FLG_STATIC) == 0) && ((sig->callConv & CORINFO_CALLCONV_EXPLICITTHIS) == 0) &&
-        !((opcode == CEE_NEWOBJ) && (newobjThis == nullptr)))
+    if (hasThis)
     {
         GenTree* obj;
 

src/tests/JIT/Regression/JitBlue/Runtime_73615/Runtime_73615.cs

@@ -0,0 +1,60 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Reference source for Runtime_73615.il.
+
+using InlineIL;
+using System;
+using System.Runtime.CompilerServices;
+using Xunit;
+
+public class Runtime_73615
+{
+    [Fact]
+    public static int TestEntryPoint()
+    {
+        Foo(new C(101));
+
+        if (Result == 100)
+        {
+            Console.WriteLine("PASS");
+        }
+        else
+        {
+            Console.WriteLine("FAIL: Got result {0}", Result);
+        }
+
+        return Result;
+    }
+
+    public static int Result;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void Foo(C arg)
+    {
+        IL.Emit.Ldarga(nameof(arg));
+        IL.Emit.Ldarga(nameof(arg));
+        IL.Emit.Call(new MethodRef(typeof(Runtime_73615), nameof(Bar)));
+        IL.Emit.Constrained<C>();
+        IL.Emit.Callvirt(new MethodRef(typeof(C), nameof(arg.Baz)));
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static int Bar(ref C o)
+    {
+        o = new C(100);
+        return 0;
+    }
+
+    public class C
+    {
+        public C(int result) => Result = result;
+        public int Result;
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        public void Baz(int arg)
+        {
+            Runtime_73615.Result = Result;
+        }
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_73615/Runtime_73615.il

@@ -0,0 +1,105 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+.assembly extern System.Runtime { .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A ) }
+.assembly extern xunit.core { }
+.assembly extern System.Console { }
+
+.assembly Runtime_73615 { }
+
+.class public auto ansi beforefieldinit Runtime_73615
+       extends [System.Runtime]System.Object
+{
+  .class auto ansi nested public beforefieldinit C
+         extends [System.Runtime]System.Object
+  {
+    .field public int32 Result
+    .method public hidebysig specialname rtspecialname 
+            instance void  .ctor(int32 result) cil managed
+    {
+      // Code size       14 (0xe)
+      .maxstack  8
+      IL_0000:  ldarg.0
+      IL_0001:  call       instance void [System.Runtime]System.Object::.ctor()
+      IL_0006:  ldarg.0
+      IL_0007:  ldarg.1
+      IL_0008:  stfld      int32 Runtime_73615/C::Result
+      IL_000d:  ret
+    } // end of method C::.ctor
+
+    .method public hidebysig instance void 
+            Baz(int32 arg) cil managed noinlining
+    {
+      // Code size       12 (0xc)
+      .maxstack  8
+      IL_0000:  ldarg.0
+      IL_0001:  ldfld      int32 Runtime_73615/C::Result
+      IL_0006:  stsfld     int32 Runtime_73615::Result
+      IL_000b:  ret
+    } // end of method C::Baz
+
+  } // end of class C
+
+  .field public static int32 Result
+  .method public hidebysig static int32  Main() cil managed
+  {
+    .custom instance void [xunit.core]Xunit.FactAttribute::.ctor() = ( 01 00 00 00 ) 
+    .entrypoint
+    // Code size       59 (0x3b)
+    .maxstack  8
+    IL_0000:  ldc.i4.s   101
+    IL_0002:  newobj     instance void Runtime_73615/C::.ctor(int32)
+    IL_0007:  call       void Runtime_73615::Foo(class Runtime_73615/C)
+    IL_000c:  ldsfld     int32 Runtime_73615::Result
+    IL_0011:  ldc.i4.s   100
+    IL_0013:  bne.un.s   IL_0021
+
+    IL_0015:  ldstr      "PASS"
+    IL_001a:  call       void [System.Console]System.Console::WriteLine(string)
+    IL_001f:  br.s       IL_0035
+
+    IL_0021:  ldstr      "FAIL: Got result {0}"
+    IL_0026:  ldsfld     int32 Runtime_73615::Result
+    IL_002b:  box        [System.Runtime]System.Int32
+    IL_0030:  call       void [System.Console]System.Console::WriteLine(string,
+                                                                        object)
+    IL_0035:  ldsfld     int32 Runtime_73615::Result
+    IL_003a:  ret
+  } // end of method Runtime_73615::TestEntryPoint
+
+  .method private hidebysig static void  Foo(class Runtime_73615/C arg) cil managed noinlining
+  {
+    // Code size       21 (0x15)
+    .maxstack  2
+    IL_0000:  ldarga.s   arg
+    IL_0002:  ldarga.s   arg
+    IL_0004:  call       int32 Runtime_73615::Bar(class Runtime_73615/C&)
+    IL_0009:  constrained. Runtime_73615/C
+    IL_000f:  callvirt   instance void Runtime_73615/C::Baz(int32)
+    IL_0014:  ret
+  } // end of method Runtime_73615::Foo
+
+  .method private hidebysig static int32 
+          Bar(class Runtime_73615/C& o) cil managed noinlining
+  {
+    // Code size       11 (0xb)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  ldc.i4.s   100
+    IL_0003:  newobj     instance void Runtime_73615/C::.ctor(int32)
+    IL_0008:  stind.ref
+    IL_0009:  ldc.i4.0
+    IL_000a:  ret
+  } // end of method Runtime_73615::Bar
+
+  .method public hidebysig specialname rtspecialname 
+          instance void  .ctor() cil managed
+  {
+    // Code size       7 (0x7)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  call       instance void [System.Runtime]System.Object::.ctor()
+    IL_0006:  ret
+  } // end of method Runtime_73615::.ctor
+
+} // end of class Runtime_73615

src/tests/JIT/Regression/JitBlue/Runtime_73615/Runtime_73615.ilproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk.IL">
+  <PropertyGroup>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).il" />
+  </ItemGroup>
+</Project>