JIT: fix profile update when folding a switch with shared case targets

src/coreclr/jit/morph.cpp

@@ -13308,18 +13308,27 @@ Compiler::FoldResult Compiler::fgFoldConditional(BasicBlock* block)
             bool       foundVal            = false;
             bool       profileInconsistent = false;
 
+            if (block->hasProfileWeight())
+            {
+                // Use unique successor edges, as duplicate jump table entries share an edge.
+                for (FlowEdge* const succEdge : block->SuccEdges())
+                {
+                    BasicBlock* const targetBlock = succEdge->getDestinationBlock();
+                    if (targetBlock->hasProfileWeight())
+                    {
+                        targetBlock->decreaseBBProfileWeight(succEdge->getLikelyWeight());
+                        profileInconsistent |= (targetBlock->NumSucc() > 0);
+                    }
+                }
+            }
+
             for (unsigned val = 0; val < jumpCnt; val++, jumpTab++)
             {
                 FlowEdge* curEdge = *jumpTab;
 
                 assert(curEdge->getDestinationBlock()->countOfInEdges() > 0);
 
                 BasicBlock* const targetBlock = curEdge->getDestinationBlock();
-                if (block->hasProfileWeight() && targetBlock->hasProfileWeight())
-                {
-                    targetBlock->decreaseBBProfileWeight(curEdge->getLikelyWeight());
-                    profileInconsistent |= (targetBlock->NumSucc() > 0);
-                }
 
                 // If val matches switchVal or we are at the last entry and
                 // we never found the switch value then set the new jump dest

src/tests/JIT/Regression_ro_2/Runtime_134896.cs

@@ -0,0 +1,28 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.CompilerServices;
+using Xunit;
+
+public class Runtime_134896
+{
+    private static int Zero() => 0;
+
+    [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
+    private static int Test(int a)
+    {
+        switch (Zero())
+        {
+            default: return a + 2;
+            case 0: case 1: return a;
+            case 2: return a + 1;
+            case 3: return a * 3;
+        }
+    }
+
+    [Fact]
+    public static void TestEntryPoint()
+    {
+        Assert.Equal(5, Test(5));
+    }
+}