[clr-interp] Fix switch statement stack slot handling

src/coreclr/interpreter/compiler.cpp

@@ -6156,26 +6156,48 @@ void InterpCompiler::GenerateCode(CORINFO_METHOD_INFO* methodInfo)
                 m_ip++;
                 uint32_t n = getU4LittleEndian(m_ip);
                 // Format of switch instruction is opcode + srcVal + n + T1 + T2 + ... + Tn
-                AddInsExplicit(INTOP_SWITCH, n + 3);
-                m_pLastNewIns->data[0] = n;
                 m_ip += 4;
                 const uint8_t *nextIp = m_ip + n * 4;
                 m_pStackPointer--;
-                m_pLastNewIns->SetSVar(m_pStackPointer->var);
                 InterpBasicBlock **targetBBTable = (InterpBasicBlock**)AllocMemPool(sizeof (InterpBasicBlock*) * n);
+                uint32_t *targetOffsets = (uint32_t*)AllocMemPool(sizeof (uint32_t) * n);
 
                 for (uint32_t i = 0; i < n; i++)
                 {
                     int32_t offset = getU4LittleEndian(m_ip);
                     uint32_t target = (uint32_t)(nextIp - m_pILCode + offset);
                     InterpBasicBlock *targetBB = m_ppOffsetToBB[target];
                     assert(targetBB);
-
-                    InitBBStackState(targetBB);
+                    targetOffsets[i] = target;
                     targetBBTable[i] = targetBB;
-                    LinkBBs(m_pCBB, targetBB);
                     m_ip += 4;
                 }
+
+                // Sort the targetOffsets array so that we can easily skip duplicates
+                qsort(targetOffsets, n, sizeof(uint32_t), [](const void* a, const void* b) {
+                    uint32_t valA = *(const uint32_t*)a;
+                    uint32_t valB = *(const uint32_t*)b;
+                    return (valA < valB) ? -1 : (valA > valB) ? 1 : 0;
+                });
+
+                // Setup so that we can safely branch to each target
+                uint32_t lastOffset = UINT32_MAX;
+                for (uint32_t i = 0; i < n; i++)
+                {
+                    if (targetOffsets[i] != lastOffset)
+                    {
+                        lastOffset = targetOffsets[i];
+                        InterpBasicBlock *targetBB = m_ppOffsetToBB[targetOffsets[i]];
+                        assert(targetBB);
+                        EmitBBEndVarMoves(targetBB);
+                        InitBBStackState(targetBB);
+                        LinkBBs(m_pCBB, targetBB);
+                    }
+                }
+
+                AddInsExplicit(INTOP_SWITCH, n + 3);
+                m_pLastNewIns->data[0] = n;
+                m_pLastNewIns->SetSVar(m_pStackPointer->var);
                 m_pLastNewIns->info.ppTargetBBTable = targetBBTable;
                 break;
             }

src/tests/JIT/Regression/CLR-x86-JIT/V1-M11-Beta1/b44861/b44861_2.il

@@ -0,0 +1,100 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+
+
+
+
+.assembly extern mscorlib { }
+.assembly extern System.Console
+{
+  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )
+  .ver 4:0:0:0
+}
+.assembly 'b44861_2'// as "b"
+{
+
+
+  //                                                                                  bool) = ( 01 00 00 01 00 00 ) 
+
+
+}
+.assembly extern xunit.core {}
+// MVID: {0573B9C2-3980-4A83-9B01-889CCC1D6FBC}
+.namespace Test
+{
+  .class public auto ansi App
+         extends [mscorlib]System.Object
+  {
+    .method public hidebysig static int32
+            Main() il managed
+    {
+    .custom instance void [xunit.core]Xunit.FactAttribute::.ctor() = (
+        01 00 00 00
+    )
+    .entrypoint
+    // Code size       31 (0x1f)
+    .maxstack  6
+            //init counter with -1
+            ldc.i4.m1
+        first_again:
+            ldc.i4.1
+            add
+            //print out counter
+            ldstr    "first_again value is "
+            call      void [System.Console]System.Console::Write(class [mscorlib]System.String)
+            dup
+            call      void [System.Console]System.Console::WriteLine(int32)
+            dup
+            brtrue do_switch
+            pop
+            ldc.i4.m1
+          again:
+            //increment counter
+            ldc.i4.1
+            add
+            //print out counter
+            ldstr    "value is "
+            call      void [System.Console]System.Console::Write(class [mscorlib]System.String)
+            dup
+            call      void [System.Console]System.Console::WriteLine(int32)
+        do_switch:
+              //make a switch
+            dup
+            switch     (first_again, first_again, first_again, again, again, again, stop)
+            //switch worked incorrectly
+            //throw an exception
+            newobj    instance void [mscorlib]System.Exception::.ctor()
+            throw
+          stop:
+              //check counter
+              //we should reach here when counter=6
+              ldc.i4 6
+              ceq
+              brfalse wrong
+              ldstr    "passed"
+              call      void [System.Console]System.Console::Write(class [mscorlib]System.String)
+              br done
+          wrong:
+              ldstr    "failed"
+              call      void [System.Console]System.Console::Write(class [mscorlib]System.String)
+          done:
+              ldc.i4 100
+        ret
+    } // end of method 'App::Main'
+
+    .method public hidebysig specialname rtspecialname 
+            instance void .ctor() il managed
+    {
+      // Code size       7 (0x7)
+      .maxstack  8
+      IL_0000:  ldarg.0
+      IL_0001:  call       instance void [mscorlib]System.Object::.ctor()
+      IL_0006:  ret
+    } // end of method 'App::.ctor'
+
+  } // end of class 'App'
+
+} // end of namespace 'Test'
+
+//*********** DISASSEMBLY COMPLETE ***********************

src/tests/JIT/Regression/CLR-x86-JIT/V1-M11-Beta1/b44861/b44861_2.ilproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk.IL">
+  <PropertyGroup>
+    <CLRTestPriority>1</CLRTestPriority>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>PdbOnly</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).il" />
+  </ItemGroup>
+</Project>