[JIT] Fixed improper peephole zero-extension removal when cdq/cwde instructions are involved

src/coreclr/jit/emitinl.h

@@ -33,6 +33,12 @@ inline bool emitter::instrHasImplicitRegPairDest(instruction ins)
     return (ins == INS_mulEAX) || (ins == INS_imulEAX) || (ins == INS_div) || (ins == INS_idiv);
 }
 
+/* static */
+inline bool emitter::instrHasImplicitRegSingleDest(instruction ins)
+{
+    return (ins == INS_cdq) || (ins == INS_cwde);
+}
+
 // Because we don't actually have support for encoding these 3-op
 // multiplies we fake it with special opcodes.  Make sure they are
 // contiguous.

src/coreclr/jit/emitpub.h

@@ -102,6 +102,7 @@ UNATIVE_OFFSET emitDataSize();
 static bool instrIs3opImul(instruction ins);
 static bool instrIsExtendedReg3opImul(instruction ins);
 static bool instrHasImplicitRegPairDest(instruction ins);
+static bool instrHasImplicitRegSingleDest(instruction ins);
 static void      check3opImulValues();
 static regNumber inst3opImulReg(instruction ins);
 static instruction inst3opImulForReg(regNumber reg);

src/coreclr/jit/emitxarch.cpp

@@ -526,6 +526,16 @@ bool emitter::AreUpper32BitsZero(regNumber reg)
             }
         }
 
+        // This is a special case for cdq/cdqe/cwde.
+        // They always write to and sign-extend RAX.
+        if (instrHasImplicitRegSingleDest(id->idIns()))
+        {
+            if (reg == REG_RAX)
+            {
+                return PEEPHOLE_ABORT;
+            }
+        }
+
         switch (id->idInsFmt())
         {
             case IF_RWR:

src/tests/JIT/opt/Regressions/Regression6.cs

@@ -0,0 +1,40 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Generated by Fuzzlyn v1.5 on 2023-02-26 16:54:59
+// Run on X64 Linux
+// Seed: 15812590312404596729
+public class C0
+{
+    public ulong F2;
+    public C0(ulong f2)
+    {
+        F2 = f2;
+    }
+}
+
+public class Program
+{
+    public static ushort s_2;
+    public static C0 s_7;
+    public static int Main()
+    {
+        ulong result = 1234;
+        for (int vr0 = 0; vr0 < 2; vr0++)
+        {
+            s_7 = M5();
+            ulong vr1 = s_7.F2;
+            result = vr1;
+        }
+
+        if (result != 18446744069414584320)
+            return 0;
+
+        return 100;
+    }
+
+    public static C0 M5()
+    {
+        return new C0(~(ulong)(4294967295U & (-(1 % (s_2-- | 1)))));
+    }
+}

src/tests/JIT/opt/Regressions/Regression6.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>