Avoid discarding upper bits when folding GT_SWITCH (#69986)

src/coreclr/jit/fgopt.cpp

@@ -3221,8 +3221,10 @@ bool Compiler::fgOptimizeSwitchBranches(BasicBlock* block)
         if (verbose)
         {
             printf("\nConverting a switch (" FMT_BB ") with only one significant clause besides a default target to a "
-                   "conditional branch\n",
+                   "conditional branch. Before:\n",
                    block->bbNum);
+
+            gtDispTree(switchTree);
         }
 #endif // DEBUG
 
@@ -3247,6 +3249,9 @@ bool Compiler::fgOptimizeSwitchBranches(BasicBlock* block)
         block->bbJumpDest = block->bbJumpSwt->bbsDstTab[0];
         block->bbJumpKind = BBJ_COND;
 
+        JITDUMP("After:\n");
+        DISPNODE(switchTree);
+
         return true;
     }
     return returnvalue;

src/coreclr/jit/morph.cpp

@@ -14922,18 +14922,16 @@ Compiler::FoldResult Compiler::fgFoldConditional(BasicBlock* block)
 
         noway_assert(lastStmt->GetRootNode()->gtOper == GT_SWITCH);
 
-        /* Did we fold the conditional */
+        // Did we fold the conditional
 
         noway_assert(lastStmt->GetRootNode()->AsOp()->gtOp1);
-        GenTree* condTree;
-        condTree = lastStmt->GetRootNode()->AsOp()->gtOp1;
-        GenTree* cond;
-        cond = condTree->gtEffectiveVal(true);
+        GenTree* condTree = lastStmt->GetRootNode()->AsOp()->gtOp1;
+        GenTree* cond     = condTree->gtEffectiveVal(true);
 
         if (cond->OperIsConst())
         {
-            /* Yupee - we folded the conditional!
-             * Remove the conditional statement */
+            // Yupee - we folded the conditional!
+            // Remove the conditional statement
 
             noway_assert(cond->gtOper == GT_CNS_INT);
 
@@ -14951,17 +14949,13 @@ Compiler::FoldResult Compiler::fgFoldConditional(BasicBlock* block)
                 result = FoldResult::FOLD_REMOVED_LAST_STMT;
             }
 
-            /* modify the flow graph */
+            // modify the flow graph
 
-            /* Find the actual jump target */
-            unsigned switchVal;
-            switchVal = (unsigned)cond->AsIntCon()->gtIconVal;
-            unsigned jumpCnt;
-            jumpCnt = block->bbJumpSwt->bbsCount;
-            BasicBlock** jumpTab;
-            jumpTab = block->bbJumpSwt->bbsDstTab;
-            bool foundVal;
-            foundVal = false;
+            // Find the actual jump target
+            size_t       switchVal = (size_t)cond->AsIntCon()->gtIconVal;
+            unsigned     jumpCnt   = block->bbJumpSwt->bbsCount;
+            BasicBlock** jumpTab   = block->bbJumpSwt->bbsDstTab;
+            bool         foundVal  = false;
 
             for (unsigned val = 0; val < jumpCnt; val++, jumpTab++)
             {
@@ -14976,20 +14970,20 @@ Compiler::FoldResult Compiler::fgFoldConditional(BasicBlock* block)
                 {
                     if (curJump != block->bbNext)
                     {
-                        /* transform the basic block into a BBJ_ALWAYS */
+                        // transform the basic block into a BBJ_ALWAYS
                         block->bbJumpKind = BBJ_ALWAYS;
                         block->bbJumpDest = curJump;
                     }
                     else
                     {
-                        /* transform the basic block into a BBJ_NONE */
+                        // transform the basic block into a BBJ_NONE
                         block->bbJumpKind = BBJ_NONE;
                     }
                     foundVal = true;
                 }
                 else
                 {
-                    /* Remove 'block' from the predecessor list of 'curJump' */
+                    // Remove 'block' from the predecessor list of 'curJump'
                     fgRemoveRefPred(curJump, block);
                 }
             }

src/tests/JIT/Regression/JitBlue/Runtime_68568/Runtime_68568.il

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Metadata version: v4.0.30319
+.assembly extern System.Runtime
+{
+  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )                         // .?_....:
+  .ver 7:0:0:0
+}
+.assembly extern System.Console
+{
+  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )                         // .?_....:
+  .ver 7:0:0:0
+}
+.assembly playground
+{
+}
+
+// =============== CLASS MEMBERS DECLARATION ===================
+
+.class public auto ansi beforefieldinit Runtime_68568
+       extends [System.Runtime]System.Object
+{
+  .method public hidebysig static int32  Main() cil managed
+  {
+    .entrypoint
+    // Code size       79 (0x4f)
+    .maxstack  2
+    .locals init (bool V_0)
+
+// Code equivalent to the following, except without the
+// int cast that C# adds on switch cases.
+//
+// switch (unchecked((nuint)0x100000000))
+// {
+//     case 0:
+//         pass = sizeof(nint) == 4;
+//         break;
+//     case 1:
+//         pass = false;
+//         break;
+//     default:
+//         pass = sizeof(nint) == 8;
+//         break;
+// }
+//
+// if (pass)
+// {
+//     Console.WriteLine("PASS");
+//     return 100;
+// }
+//
+// Console.WriteLine("FAIL");
+// return -1;
+
+
+    IL_0000:  ldc.i4.0
+    IL_0001:  stloc.0
+    IL_0002:  ldc.i8     0x100000000
+    IL_000b:  conv.u
+    IL_000c:  switch     (
+                          IL_0025,
+                          IL_0031)
+    IL_0019:  sizeof     [System.Runtime]System.IntPtr
+    IL_001f:  ldc.i4.8
+    IL_0020:  ceq
+    IL_0022:  stloc.0
+    IL_0023:  br.s       IL_0033
+
+    IL_0025:  sizeof     [System.Runtime]System.IntPtr
+    IL_002b:  ldc.i4.4
+    IL_002c:  ceq
+    IL_002e:  stloc.0
+    IL_002f:  br.s       IL_0033
+
+    IL_0031:  ldc.i4.0
+    IL_0032:  stloc.0
+    IL_0033:  ldloc.0
+    IL_0034:  brfalse.s  IL_0043
+
+    IL_0036:  ldstr      "PASS"
+    IL_003b:  call       void [System.Console]System.Console::WriteLine(string)
+    IL_0040:  ldc.i4.s   100
+    IL_0042:  ret
+
+    IL_0043:  ldstr      "FAIL"
+    IL_0048:  call       void [System.Console]System.Console::WriteLine(string)
+    IL_004d:  ldc.i4.m1
+    IL_004e:  ret
+  } // end of method Runtime_68568::Main
+
+  .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_68568::.ctor
+
+} // end of class Runtime_68568
+
+
+// =============================================================
+
+// *********** DISASSEMBLY COMPLETE ***********************

src/tests/JIT/Regression/JitBlue/Runtime_68568/Runtime_68568.ilproj

+<Project Sdk="Microsoft.NET.Sdk.IL">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).il" />
+  </ItemGroup>
+</Project>

src/tests/issues.targets

@@ -2201,6 +2201,9 @@
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/Runtime_70259/Runtime_70259/*">
             <Issue>https://github.com/dotnet/runtime/issues/70279</Issue>
         </ExcludeList>
+        <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/Runtime_68568/Runtime_68568/*">
+            <Issue>Tests coreclr's handling of switches on natively sized integers</Issue>
+        </ExcludeList>
     </ItemGroup>
 
     <!-- Known failures for mono runtime on Windows -->